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May 16,
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Metal Oxide Film Resistors are fundamental electronic components known for their precision, stability, and reliability in a wide range of applications. This article aims to provide an in-depth exploration of Metal Oxide Film Resistors, their construction, characteristics, and the crucial role they play in ensuring accuracy and stability in electronic circuits.
Metal Oxide Film Resistors are passive electrical components designed to limit or control the flow of electric current within a circuit. They are constructed using a ceramic substrate coated with a thin film of metal oxide, typically tin oxide or ruthenium oxide. The metal oxide film acts as the resistive element, providing the desired resistance value.
Metal Oxide Film Resistors find widespread use in numerous electronic applications, including:
Metal glazed Film Resistor is vital components in electronic circuits, offering precise resistance values, temperature stability, low noise, and high power handling capacity. Their reliability and long-term stability make them invaluable in various industries, including audio systems, measurement equipment, medical devices, industrial control systems, and telecommunications. With their ability to provide accurate and stable resistance performance, Metal Oxide Film Resistors continue to be an essential building block for engineers and designers, contributing to the overall precision and reliability of electronic systems.
Rob French (Scrape)
#
I realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
Edwin Houwertjes
#
Hi Rob,
It is hard t find non inductive resistors. Even the one most people refer to as being non inductive probably have some tuning spiral on them.
If you use SMD resistors there is a different kind of tuning so these should be better than the old fashioned tru hole axial resistors.
What you really do no want is wire wound resistors.
Standard metal film resistors do have a tuning spiral
Even carbon film resistors most of the time have a spiral but most resistors i checked have less turns.
Carbon-composite resistors should have types that are non inductive, but if you want to be sure laak at the RF-resistor section of your supplier.
Yes they are expensive and you will probably end up at an RF electronics specialist.
So should you buy expensive resistors.... I guess not, if you use them on HF even the spiraled metal film resistors probably work well enough. On VHF you probably should better use carbon film resistors or change to SMD.
It is much more important to keep the leads short (keep the resistor in a antenna connector) than picking the best resistor.
You probably also have some dummy load around you so giving the analyzer an extra test with a non inductive resistor to check for a good 1:1 value always an option.
Oh, and measure your dummy load using a multimeter, not probably will not be an exact 50 ohms but I guess it should not show over 1.2:1
Anyway, for HF any resistor that is not wire wound will probably work well enough.
73'
Edwin
Sheldon Howard
#
Hi Edwin,
let me tell you about a little trick we used to do in the old days (I've been a ham since ) and one you can do today and maybe solve your problem.
Buy a few 56 ohm 10 watt old style carbon resistors, probably need to get them from a surplus store like All Electronics in LA or Murphy's in El Cajon, CA.
While hooked up to an ohm meter, slowly file (or use a Dremel tool) to file little cuts into the resistor and observe the resistance decrease as you cut, till you get to 50 ohms.
If the resistor is too large to mount on the PC board, you will probably need to place it off the board. Of course you can use smaller resistors, 5 watt or even 1 watt, but it is more difficult.
Hope this helps, let me know.
toggle quoted message
Show quoted textOn Sun, Jan 5, , 9:43 PM Edwin Houwertjes < ehouwertjes@... > wrote:
Hi Rob,
It is hard t find non inductive resistors. Even the one most people refer to as being non inductive probably have some tuning spiral on them.
If you use SMD resistors there is a different kind of tuning so these should be better than the old fashioned tru hole axial resistors.
What you really do no want is wire wound resistors.
Standard metal film resistors do have a tuning spiral
Even carbon film resistors most of the time have a spiral but most resistors i checked have less turns.
Carbon-composite resistors should have types that are non inductive, but if you want to be sure laak at the RF-resistor section of your supplier.
Yes they are expensive and you will probably end up at an RF electronics specialist.
So should you buy expensive resistors.... I guess not, if you use them on HF even the spiraled metal film resistors probably work well enough. On VHF you probably should better use carbon film resistors or change to SMD.
It is much more important to keep the leads short (keep the resistor in a antenna connector) than picking the best resistor.
You probably also have some dummy load around you so giving the analyzer an extra test with a non inductive resistor to check for a good 1:1 value always an option.
Oh, and measure your dummy load using a multimeter, not probably will not be an exact 50 ohms but I guess it should not show over 1.2:1
Anyway, for HF any resistor that is not wire wound will probably work well enough.
73'
Edwin
Tom, wb6b
#
slowly file (or use a Dremel tool) to file little cuts into the resistorWow, I remember "tuning" 1/2 watt carbon composite resistors in the old days. Then would spray them with lacquer to protect the cut.
On Mon, Jan 6, at 12:19 AM, Sheldon Howard wrote:Wow, I remember "tuning" 1/2 watt carbon composite resistors in the old days. Then would spray them with lacquer to protect the cut.I think the value went up as you filed away on the resistor. Was so surprised the first time I was filing a resistor, only to find out it was a new fangled carbon film resistor and right away it became hard to file and cracked in half.Tom, wb6b
KD4OBQ#
While at a Hamfest or estate sale or even a surplus shop look for some terminators as there are so many different varieties to choose from. I have several Narda Microline of different shapes and sizes. Also if you see what looks like a blank or dust cover and has a center pin it may be one. Just check it with an ohm meter as I have several with BNC and SMA. The Narda's have N and BNC connectors and are good from DC to 12 Ghz. I only gave a few buks each for them through the years. I have probably given most of them away as they make good gifts for newbies getting into RF but keep a few on the work bench.
It was a sad time when they got away from Carbon Comp resistors however we learn to adjust.
Take care
Pat
#
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) <robert@...> wrote:
I realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
Brian Bowling#
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
toggle quoted message
Show quoted textOn Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
jjpurdumRob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
#
eBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling <bowlingb@...> wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
toggle quoted message
Show quoted textOn Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
Roy Appleton
#
Roy
WA0YMH
Jack, Are these the resistors you use to make the dummy load in your little watt meter and if so were they oil-cooled or just air-cooled.
toggle quoted message
Show quoted textOn Mon, Jan 6, , 9:40 AM jjpurdum via Groups.Io > wrote:
jjpurdumeBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling < bowlingb@... > wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
On Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
#
No. The Mini DL that's in the new book uses a single high-power resistor and, unlike the "big" DL, it is meant for 25W or less. We used this:
which is similar to eBay #
and costs less than $8. Note this is rated at 250W, but it you apply that much power to it, the top will go into near-earth orbit. We rated this at 25W with a large heatsink, and even then warn to keep the key-down time to less than 10 seconds if possible. The advantage is that the unit:
is that it is small enough to fit in a shirt pocket...hard to do with a quart can filled with mineral oil. It also has a small OLED that shows the power. You can see the RF resistor just below the orange wire. The resistor is bolted to the heat sink on the back of the case:
By not centering the heat sink, you can actually have it tilt towards you for easier viewing of the power display. (The picture was taken before I bolted it in place just to give an idea of its size. It is actually closer to the top edge than shown here.)
The 150W version is featured in the Nov., , issue of QST.
Jack, W8TEE
On Monday, January 6, , 11:21:08 AM EST, Roy Appleton <twelveoclockhigh@...> wrote:
Roy
WA0YMH
Jack, Are these the resistors you use to make the dummy load in your little watt meter and if so were they oil-cooled or just air-cooled.
toggle quoted message
Show quoted textOn Mon, Jan 6, , 9:40 AM jjpurdum via Groups.Io > wrote:
eBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling < bowlingb@... > wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
On Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
Graham, VE3GTC
#
cheers, Graham ve3gtc
Unfortunately all are SMD or flange mount but are not difficult to work with.
Proper RF suitable 50 ohm resistors / loads are easily available and cost effective, low power between $5 and $10 and higher power devices more. For example, here are a few links:
toggle quoted message
Show quoted textOn Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
Roy Appleton
#
Roy
WA0YMH
Jack, thanks for the info!
toggle quoted message
Want more information on metal oxide film resistor? Feel free to contact us.
Show quoted textOn Mon, Jan 6, , 10:49 AM jjpurdum via Groups.Io > wrote:
Brian BowlingNo. The Mini DL that's in the new book uses a single high-power resistor and, unlike the "big" DL, it is meant for 25W or less. We used this:
which is similar to eBay #
and costs less than $8. Note this is rated at 250W, but it you apply that much power to it, the top will go into near-earth orbit. We rated this at 25W with a large heatsink, and even then warn to keep the key-down time to less than 10 seconds if possible. The advantage is that the unit:
is that it is small enough to fit in a shirt pocket...hard to do with a quart can filled with mineral oil. It also has a small OLED that shows the power. You can see the RF resistor just below the orange wire. The resistor is bolted to the heat sink on the back of the case:
By not centering the heat sink, you can actually have it tilt towards you for easier viewing of the power display. (The picture was taken before I bolted it in place just to give an idea of its size. It is actually closer to the top edge than shown here.)
The 150W version is featured in the Nov., , issue of QST.
Jack, W8TEE
On Monday, January 6, , 11:21:08 AM EST, Roy Appleton < twelveoclockhigh@... > wrote:
Roy
WA0YMH
Jack, Are these the resistors you use to make the dummy load in your little watt meter and if so were they oil-cooled or just air-cooled.
On Mon, Jan 6, , 9:40 AM jjpurdum via Groups.Io > wrote:
eBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling < bowlingb@... > wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
On Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
#
Thank you!
toggle quoted message
Show quoted textOn Mon, Jan 6, at 10:40 AM jjpurdum via Groups.Io > wrote:
eBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling < bowlingb@... > wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
On Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
Tom, wb6b
#
Proper RF suitable 50 ohm resistors / loads are easily available and cost effective,Here is a power resistor I used in another dummy load. These are in a TO-220 style package. These are similar to what my MFJ antenna auto tuner uses.
On Mon, Jan 6, at 08:50 AM, Graham, VE3GTC wrote:Here is a power resistor I used in another dummy load. These are in a TO-220 style package. These are similar to what my MFJ antenna auto tuner uses.In this case I used two resistors in parallel and have some other resistive dividers for an RF sampling port and a RF voltage measurement.
Dave VE3LHO
#
Jack,
You derated this to 10% of its nominal rating (25W versus the "rated" 250W). I'm curious how you came to this conclusion. Would you use the same factor for the "100W" resistors that are also commonly available on ebay?
I've got some of the 100W ones on the way. I wasn't expecting them to actually handle 100W but I was thinking I might use them at more than 10W. On the other hand I'd rather not have bits of resister flying around :-)
Thanks,
Dave L.
toggle quoted message
Show quoted text
No. The Mini DL that's in the new book uses a single high-power resistor and, unlike the "big" DL, it is meant for 25W or less. We used this:
which is similar to eBay #
and costs less than $8. Note this is rated at 250W, but it you apply that much power to it, the top will go into near-earth orbit. We rated this at 25W with a large heatsink, and even then warn to keep the key-down time to less than 10 seconds if possible. The advantage is that the unit:
is that it is small enough to fit in a shirt pocket...hard to do with a quart can filled with mineral oil. It also has a small OLED that shows the power. You can see the RF resistor just below the orange wire. The resistor is bolted to the heat sink on the back of the case:
By not centering the heat sink, you can actually have it tilt towards you for easier viewing of the power display. (The picture was taken before I bolted it in place just to give an idea of its size. It is actually closer to the top edge than shown here.)
The 150W version is featured in the Nov., , issue of QST.
Jack, W8TEE
On Monday, January 6, , 11:21:08 AM EST, Roy Appleton <twelveoclockhigh@...> wrote:
Roy
WA0YMH
Jack, Are these the resistors you use to make the dummy load in your little watt meter and if so were they oil-cooled or just air-cooled.
On Mon, Jan 6, , 9:40 AM jjpurdum via Groups.Io > wrote:
eBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling < bowlingb@... > wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
On Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
On Mon, Jan 6, at 08:37 AM, jjpurdum wrote:
jjpurdum#
Dave:
What we did was measure the case temperature with a infrared thermometer as we applied greater levels of power. When it got to 100° in less than a minute, we deemed that power level too high. From a cold start, the 250W resistor was "on the edge" at 50W of power. We just decided that 30W was about all it could handle safely. It's an arbitrary and conservative measure.
Jack, W8TEE
On Tuesday, January 7, , 12:12:14 PM EST, Dave VE3LHO <dave@...> wrote:
Jack,
You derated this to 10% of its nominal rating (25W versus the "rated" 250W). I'm curious how you came to this conclusion. Would you use the same factor for the "100W" resistors that are also commonly available on ebay?
I've got some of the 100W ones on the way. I wasn't expecting them to actually handle 100W but I was thinking I might use them at more than 10W. On the other hand I'd rather not have bits of resister flying around :-)
Thanks,
Dave L.
toggle quoted message
Show quoted text
No. The Mini DL that's in the new book uses a single high-power resistor and, unlike the "big" DL, it is meant for 25W or less. We used this:
which is similar to eBay #
and costs less than $8. Note this is rated at 250W, but it you apply that much power to it, the top will go into near-earth orbit. We rated this at 25W with a large heatsink, and even then warn to keep the key-down time to less than 10 seconds if possible. The advantage is that the unit:
is that it is small enough to fit in a shirt pocket...hard to do with a quart can filled with mineral oil. It also has a small OLED that shows the power. You can see the RF resistor just below the orange wire. The resistor is bolted to the heat sink on the back of the case:
By not centering the heat sink, you can actually have it tilt towards you for easier viewing of the power display. (The picture was taken before I bolted it in place just to give an idea of its size. It is actually closer to the top edge than shown here.)
The 150W version is featured in the Nov., , issue of QST.
Jack, W8TEE
On Monday, January 6, , 11:21:08 AM EST, Roy Appleton <twelveoclockhigh@...> wrote:
Roy
WA0YMH
Jack, Are these the resistors you use to make the dummy load in your little watt meter and if so were they oil-cooled or just air-cooled.
On Mon, Jan 6, , 9:40 AM jjpurdum via Groups.Io > wrote:
eBay #
.
Jack, W8TEE
On Monday, January 6, , 10:32:43 AM EST, Brian Bowling < bowlingb@... > wrote:
Jack,
You wouldn't happen to have saved the link did you?
Brian
N8BDB
On Mon, Jan 6, at 9:49 AM jjpurdum via Groups.Io > wrote:
Rob:
It is confusing and I did not write the warning clearly. The DL is meant for HF work and metal film resistors are fine and what I used. Some resistors actually do have a small diameter wire coil inside them which is not what you want. I just saw 20 Ω 3W metal film resistors for about $5 on eBay. Those should work just fine. Others have mentioned that 20 such resistors are likely not a perfect 50Ω match, but the article tells you how to compensate for that.
Jack, W8TEE
On Sunday, January 5, , 10:08:26 PM EST, Rob French (Scrape) < robert@... > wrote:
As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."
That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in
But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.
Should I go build myself a new set of calibration resistors? I'm guessing yes.
Thanks,
Rob KC4UPRI realize this is an analog question, not so much software. However, it does relate to something I saw in Jack W8TEE's excellent book, "Arduino Projects for Amateur Radio".As I was reviewing the chapter on the directional watt and SWR meter, I came across this statement regarding the 50 ohm terminating resistors: "While it is not essential that these be carbon comp resistors, they must be noninductive. Carbon film resistors tend to be noninductive. Metal oxide and metal film resistors are trimmed with a laser-cut spiral making them highly inductive."That got me worried, because I am using a set of three metal film resistors as the calibration loads for my MR-100 antenna analyzer, which at the moment is the only tool I have to check my antenna SWR. (This is one of those "bare PCB between two sheets of acrylic", ~$50 online analyzers.) Specifically, based on what I read in this blog entry about calibrating the analyzer ("... modern metal film resistors are made to very good accuracy ..."), I purchased metal film 50 ohm (Vishay) 150 ohm (IRC/TT) , and 274 ohm (IRC/TT) resistors. Now I am concerned that the whole boot-strapping of my antenna analysis may be off, and that my antenna is not as safe (SWR) for my tuner-less rig as I thought...But then, I also read in Jack's book, chapter 6 regarding the dummy load, "Essentially, the DL is a group of noninductive (metal film or metal oxide) resistors..." So now I'm a little confused. I suspect that the answer is really, "it depends", and that some metal film/oxide resistors are inductive, some aren't. I did read about the spiral construction, so it would certainly make sense to me that they are inductive.Should I go build myself a new set of calibration resistors? I'm guessing yes.Thanks,Rob KC4UPR
On Mon, Jan 6, at 08:37 AM, jjpurdum wrote:
Terry VK5TM
#
If you look up the data sheet for these 250W resistors, you will see the 250w rating is when suitably heatsinked and Jack's heatsink is only a fraction of the needed size to sustain the 250w level.
Derating to 25w with the small heatsink is a smart move.
Otherwise you are back to submerging it in a tin of oil which kind of defeats the purpose.
On the original post, metal film resistors were once recommended as replacements for (supposedly) hard to find carbon resistors in RF use.
Dave VE3LHO
#
Arbitrary perhaps but it sounds like it had some data behind the decision. Thanks for explanation.
73
toggle quoted message
Show quoted text
Dave:
What we did was measure the case temperature with a infrared thermometer as we applied greater levels of power. When it got to 100° in less than a minute, we deemed that power level too high. From a cold start, the 250W resistor was "on the edge" at 50W of power. We just decided that 30W was about all it could handle safely. It's an arbitrary and conservative measure.
Jack, W8TEE
On Tue, Jan 7, at 09:20 AM, jjpurdum wrote:
Dave VE3LHO
#
Yes derating makes good sense for these resistors. I was curious about the process used to determine how much to derate.
toggle quoted message
Show quoted textIf you look up the data sheet for these 250W resistors, you will see the 250w rating is when suitably heatsinked and Jack's heatsink is only a fraction of the needed size to sustain the 250w level.
Derating to 25w with the small heatsink is a smart move.
Otherwise you are back to submerging it in a tin of oil which kind of defeats the purpose.
On the original post, metal film resistors were once recommended as replacements for (supposedly) hard to find carbon resistors in RF use.
On Tue, Jan 7, at 02:44 PM, Terry VK5TM wrote:
The company is the world’s best all industial resistor manufacturer supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.