How to make a Ham Radio RF Dummy load using a Low Pass filter Conversion
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- Опубликовано: 3 окт 2024
- Here is a nifty way to re-purpose a useless low pass filter into a useful 50 ohm RF dummy load. Depending on the low pass cabinet and whatever resistors you have on hand a very powerful device can be constructed. Check out the current prices of dummy loads and you will be shocked! Presented here, a cheaper choice. Remember, this is just a Tech Tip, you can construct this device as you see fit. I am just recommending this method. Hope you like.
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I used a one gallon paint can, hung a large 50 ohm non-inductive resistor on the so239 and filled the can with mineral oil (most expensive part).
Thanks for the video.
I believe that the large discarded resistor in the MFJ unit is a very good non-inductive resistor.
Dunk it in a gallon of oil (if it will fit inside the can), and it would make a very decent 1.5 kW load. The Cantenna used a 90 watt resistor such as this, and it's an ol' standby.
COOL! The Ungar SNOZZERAMUS got its own theme this time!
This is a very useful video, IMO. Thank you, Terry! And BIG points for Joe Jackson!
Thanks for this video, just ordered the same filter for 30 and resistors for 15 dollars. I need a good dummy load but at a reasonable cost and this sure fits into this disabled pensioners budget...👍
"Luckily this is held together with about....3000 screws". That literally made me laugh. Snauzeramous returns! Thanks Terry.
Always need a few puns to keep the vid fun!
The problem is found when you realize those are typically wire-wound resistors, and are introducing a reactive factor.
Nothing wrong with your connectors or coax, you just build a BETTER dummy load than a overpriced MFJ, good job.
Bad idea. Those "golden" resistors are actually inductances, as those are wire resistors :( Parallel connection reduces inductance in 1/N proportion, but it still remains noticeable. So load resistance value is frequency-dependent here
i was just going to type all about inductance of wire wound resistors not being a good idea, you should only use carbon based resistors, inductance will to use his own phrase create a splatter box. has a wire wound resistors get hot the tolerances can changes significantly making them a bad choice for this job.
Those resistors he used are wound to be relatively non-inductive. I just measured a similar one, and it's showing maybe 3µH @ 100khz. not sure what that would be at his transmitter's frequency.
This golden resistors are wire-wound which operates only up to 100KHz, not good for a dummy load.
I canceled Direct TV for D-Lab! Thanks buddy!
That reverse power was all about the long wires inside the box. If you can make them all as short as the mechanics will allow, that power will drop. Otherwise you could put some shunt caps in there to make the wires lowpass matched filters. You can make the caps from copper flags that you adjust by bending them. You should be able to get down below 1 watt without too much trouble.
These Dale resistors are wirewound. Heavily indutives. LU1AR
@@edgardomaffia5356 Wire wound resistors can be made non-inductive. They use two opposite wound coils so the reactance is canceled out.
@@BurrowsNE Yes, but these are not. In my case I used metal film resistors in parallel, on a 50 ohm strip line. As here. LU1AR
lu1ar.blogspot.com/2012/11/la-carga-fantasma-para-uhf-de-lu1ar.html?view=classic
Those resistors are intended to be mounted on a heat sink in order dissipate their rated power (check the data sheet). The way you have them mounted back to back in the big dummy, they won't have much heat sink. So it will work fine for lower power, or for short duration, and should be good enough for most testing. But not for full power long term...
Thanks Terry,,, nice little project and money saver.
Thanks Terry. That's what electronics is about also.
Hi Terry!! Finally got my ham ticket (Passed both Tech and General!). 73 W1NLJ
I would have left the brass plate on there for a little bit better heat sinking. Also I would spread the resistors out more for the same reason. You can use more of the enclosure as a heat sink if you spread out the resistors. Just my opinion. Thanks for the video it was nice and clear and concise.
Try putting an antenna analyzer on your dummy loads.
This is a very nice dummy load D Lab!
I'm trying to figure out how Lester claims 2000 watts out of his oil submersed dummy load.
He used 48 - 5 watt big resistors with 3 soldered in series. Then took 16 rows of the 3 in series and put them in parallel as you have done with yours and submersed them in a paint can like has been done for years.
boat anchors are pretty neat
What is the vswr?
Señor gracias por compartir sus conocimientos.saludos cordiales desde argentina.
Don't get rid of your old LPF. Try reinstalling it and you will see how reception improves.
This happens, because the FM stations (which you do not receive but are there),
desensitize and take ou of linearity the front stage. Check it!. LU1AR
Non-inductive? Maybe at close to DC. Plus look at all the wire leads you have used to connect those wirewound resistors together. As crappy as MFJ stuff is, at least they used a good carborundum resistor. Put your load on a nano VNA and show the results on YT friend.
TIP TOP TIDY JOB...!!
Very schmick indeed.
Peace from OZ
Good job! Thank you for sharing it with us.
@ 02:37 I'm so glad other people detect and alter inferior design.
Hi Terry informative video. It would be interesting to see the impedance of your load vs frequency. If you have a friend with a VNA it would be simple and quick to run a single port test just for the fun of it . 73s Joe
I have a "Snoz-a-ramus"! Ya baby!! The cheapest I could find a RF Shell was $55
I guess exists the swr test....probably this dummy load may operate at 3.5 Mhz non more ..or not .I1rr
Terrific tech tip Terry, "tanks".... :-)
All well and good but you fail to mention what band widths it covers
If those caps were 100 to 150 pf they can be used to make some EFHW antenna baluns
I hear Timtron yelling.... Hey dummy, use a dummy load!
The resistors may not be inductive but all that wiring sure is.
It seems that being wire wound resistors, they will be resonant at some frequency. even thought they are purported to be none inductive.
Nice...Like the red wine...just like me
"Non-inductive" to what frequency? There are specific ones for RF those resistors have a limit somewhere before becoming inductive. Maybe put an SWR meter inline and see if it reads 1.
Just buy a high power chip Resistor .. job done.
Tks x sharing. Very much appreciated.
The "Big Dummy" load. Now available at Sanford & Son.
:D
Now you need a custom logo for that one!
You need air flow or its going to get hot really fast.
good job.i have (27) 50w each, 50 and 100 ohms 1% resistors,so i can make a series-paralel circuit to make a 50 ohm total and 1000w power also i have a 10x5x5 box w/heat sink, i want to try a build one of those some day ,i like your videos
Everything has to be big at high power.
Nothing over 5 Watts here for 30+ years. Dummy load resistors built into a treacle tin, enjoy the treacle and use the tin.
Although built for higher power and holes punched in for air flow when I used to use 100 Watts, SWR meter reading just lifts off the end stop at 30 MHz, 1.2:1 at 50 MHz and 1.4:1 at 145 MHz, all acceptable. I made another QRP DL which shows 1.1:1 SWR at 145 MHz. A resistive type SWR meter so the tx never sees above a 2:1 SWR when tuning aerials, the downside is that it has to be taken out of circuit as it consumes half my power. Just watch for any change in other meter readings indicating a problem, nothing ever has.
It's why I use QRP gear, everything is cheaper, including the electricity bill.
Although a lot of times I use a 12 Volt rechargeable battery and solar panel.
G4GHB
I still have the Heathkir paint bucket.
Ok. I give up. What is the Gauge, name, material of the hook-up wire?
Heck, if it's just the sheet metal case you need, you could just go down to [insert your favorite home improvement store here], buy a 2' by 2' sheet of steel/aluminum, some sheet metal screws, and make your own. Home Depot even sells 12"x24" copper-plated aluminum sheets for $16. Plus a couple of bucks for a 2x2 or 2x4 to bend the metal around, if you don't happen to have a piece of scrap in the garage.
@@garybevis8691 ruclips.net/video/fJ5LZEYyjiU/видео.html
Lots of others out there, go find them yourself.
Great tops! Thanks.
So, your non-inductive resistors are carbon compound, right?
Have you got a circuit suggestion to add an "RF power" led to this? would be a nice addition to show when RF is present? nice video btw
I have the MFJ-264 (rated at 1.5kW) and they gave screwed in the SO-239 on that model.
Hey D-Lab, thank you for the build, it is a great idea! Would you consider using thermal conductive paste between the resistors and the case?
This video earned a sub. Good tip.
I now looked up the Datasheed and it says that there is also a non-inductive Version of this Resistor . If I understood it right, it is the Type "ENH".. But RER70, the Type used in this Video, seems to be not a ENH Type, but a ERH-Type, but I do not exactly know.. :/
Thanks! Nice job! 73 de K2CJB
50 ohm resistors ?
Nice one Mr T.
BUT using all of those same guts into a new 1 gal paint can from home depot and then adding 3 qts of non detergent motor oil would turn that 240w dummy of yours into a 1kw+ dummy.
OK; so you can do another dummy load on the next vidddy.
There's an idea for ya.
Even go a step farther and add a RF sampler circuit in it - too
Better still . . .
For FM BAnd 88-108Mhz, someone tested and what is the ROE?
Sounds like an SWR of about 2:1.. ( 5W to 45W ) ???
Yes, could be. I may add an internal small PF cap to lower it. Pure carbon resistors may also help, Remember, this is just a Tip for constructing, not the only way. TD
Just checked my Large Bird dummy load, has about the same reflected PWR, so I'm guessing it may error in my W4 wattmeter
OK....What's a Snauzaramus?
I guess the newer version of the mfj is "better" mine is the mfj-260C 300w and it has a much nicer so239 connector thats actually fastened with bolts, nuts and glue! But no improvement to the "ground" but it has this cage that surrounds the resistor now
hmmm maybe using wire wound resistors isnt the best choice, think about it, each resistor will act as an antenna and tho it might not be resonate on hf it might cause interference in other bands
Yes, i agree, switched to carbon, now have a flat swr
a dummy load is pure resistive, you should not use wirewound resistors as they are inductors.
I need a 2kw dummyload.. do you have any options?
hi can you check I thought those resistors were inductive ?
Yes, these are non inductive, look up the specs on Mouser
They very much look like aluminium clad wirewounds to me which have significant inductance, have you a Mouser part number?
FWIW, the load I built with 20 x 1K 3W carbon film resistors shows an SWR of close to 1.2:1 to VHF so there's something not quite right happening here...
Good music…thanks for the recommendation …. I’m down with it..what else you got. .
Hi All, Interesting video which inspired me to knock one together, I used 3 x 50 watt 5% 150R's as not planning to push too much power through it. The final measurement on my calibrated Fluke 173 is 49.8 Ohms, close enough for sure! However when I connect it after the Zetagi 203W SWR meter the SWR flies up to 7:1.. Any suggestions most welcome..
The key is to use non-inductive resistors. Otherwise the impedance will fluctuate with the frequency.
I've got one of those old low pass filters. I was gonna try to sell it but now, thanks to you, I WILL repurpose it. I've been needing a dummy load and I have a bunch of 1% resistors - 95.4 ohms, 50 ohms and 43.4 ohms with various wattage. The 95.4 ohms are 40 watt resistors. I'll have to figure out how to get them to 50 ohms. Any suggestions??? These are power resistors that can be mounted with heat sync compound. 73 from K9POW in eastern Tennessee.
at 120 watts it will heat up in a hurry. need more heatsink
Could you use 3 50ohm in series to make 150ohm load Good job btw
@goinghomesomeday1 Hi I have made one. Basically, it's for setting the SWR protection, on my ts950sdx that evaluates to about 3:1. The radio should reduce the power output and save the finals when this limit is reached. Works a treat I had to do this because I replaced the control board from a donor radio and had to go through the board so it was right with my radio that's why I needed the 150ohm dummy load total cost of 24 GBP bargain
Okay. Why is a low-pass filter worthless? My neighbor has OTA TV. We do have some analog stations here.
I'm still awaiting a reasonable reply as to why a device that served us so we'll, for so long, is trash.
I think the main reason would be modern tranceivers are far more immune to TVI than back in the day along with less spurious emissions on TX that doesn't benefit from external low pass filtering like it may have in the past.
@@kus0mak lmao
Hi D-lab Electronics can I use a resistor of the same type the brown one you have on your table for a dummy load I have one of 50 ohms from a scrapped vending machine and how many watts can it approximately hold, another person has told me that I do not can use it as the radio sees it as a coil.
how to make a dummy load support 0-3Ghz frequency? in telco i need 850Mhz to 2300Mhz
Use a microwave termination load.
Unrelated question, but I hope you can help. I have an opportunity to buy a nice 100W tube head. The amp works perfectly except for a impedance selector switch that is busted. Its a three position sliding switch. Should this be a simple fix? I'm fairly handy with basic guitar mods, but haven't done much amp work. Thanks for your time and informative videos!
Is this the switch? reverb.com/item/2976121-switch-rotary-impedance-selector-replacement-for-marshall?gclid=EAIaIQobChMI_oTT14yt4AIVErnACh3zjgZZEAQYASABEgLLyfD_BwE&gclsrc=aw.ds&pla=1
at about 7:20 you mentioned the power dissipation as about 120 W. It would be 240 watts. Are you saying 120 watts for safety reasons, it should be able to dissipate 120 watts forever and 240 with intermittent use? Just curious. Neat idea, not good for VHF or UHF but should be a great dummy load for the low bands. Thanks for the great idea.
No, he said right. When you stack the resistors in parallel the wattage becomes multiplied as to the number of the resistors.
But when in series power handling would remain the same.
He has has them in series and parallel combination; refer to the schematic on paper for clarification.
Hi I just built mine and I'm getting 5:1 swr readings out of it on 5w I used the 100w version of your resistors. Any ideas why this might be happening ?
Those look like wirewound resistors.
Well, it was a nice idea. I can't find any non-inductive 20W 150 Ohm resistors on eBay. Anybody have a link they can share? Or if I must go WW, how much inductance is too much?
There's no carbon composition resistor (non inductive) in the design shown. All you find are only wire wound resistors. But you should be using any wire wound resistors for making an rf dummy load.
Sorry terry it should be flat at least to the middle of HF 14mhz ish , looks like too many bends of wire & how none inductive are those resistors really?? unit still very useful as is though . love your dedication to old gear & feel the same -keep these old tube gear going hopefully for the next generation do the same as this gear IS fast being lost FOREVER .
Hello Will, Yes, I will refine it, this was just to share the concept.
HI Snauzaramus!
Onto many dummy loads it is written 3GHz. Are good for testing power in 136-500 MHz range ? (radios within VHF and UHF bands)
Yes, should be DC to 3 GHz.
Are you serious c.nt
Wire wound resistors can't use as RF dummy load
my light bulb is 250 watt, cost pennies and is 50 ohm .. best dummy load i ever had, whahahahahaha
Oh..I forgot…I’m going to run 8 400 ohm 100 watt wire wound resistors in parallel and and use a small fan to pull the heat out if there ever is any heat...Better than dragging a paint can with a gallon of oil around.
NO WIRE WOUND RESISTOR should be used for the dummy load.
@@subramanianr7206 interesting.. I would like to know why if you have any time to explain. I’m always trying to learn..
@@rickhunt3183 The transmitter'/receiver's characteristic impedance is 50 ohm resistive. I think you should be knowing why it's 50 ohm.
As a load for the Tx (transmitter) pure 50 ohm impedance matching is necessary because it's when there's no reactance created by either inductance or capacitance. "ELI the ICE man", the phrase to remember that voltage (E) proceeds in an inductor (L) than the current (I); in a capacitor (C) current proceeds the voltage. That's there's a phase difference between them.
An dummy load is called a dummy aerial because it offers an impedance match to the TX, but it doesn't radiate any RF to any far off distance.
A resonant antenna has both the voltage and the current in phase but would accept all the power from the TX and radiate as Electromagnetic waves in space.
A wire wound resistor would offer 50 ohm to DC but not AC.
@@subramanianr7206 Thank you for that explanation.
@@rickhunt3183 you are welcome.
Absolutely dont do this. These resistors are wire wound like a coil and have inductance. You need non inductive resistors and they are very expensive. You can buy microwave dummy load resistors 50 ohm for £10 UK pounds on ebay and rated at 250Watts and can operate up to 155deg Centigrade. Cheers from old George
The worst instructional Dummy load Video. Please do not follow this people RER70F1500R Are Vishay Wirewound resistor. RER40-RER55 Are available in non-inductive styles (type ENH) with ArytonPerry winding for lowest reactive components.
I'm sure this was a genuine mistake by the Author.
thanks for sharing this. i have thought about using the resistors you used but was not sure if they could take RF signals. so thank you. i will be building one.
Hello, On the MFJ dummy load, I changed over to 2 watt carbon resistors, 1.8K x 36 in parallel, flat SWR
Hi Terry, could you show us how to build a power attenuator from scratch for our 100w guitar tube amplifiers please??!!