RF Dummy Load - DIY

Hi all,

I've come across several occasions where someone requires a RF Dummy load for checking/testing their radios.

They can be purchased relatively cheaply new, but soon become expensive for higher wattages.

There are various DIY approaches from salt water filled pots to 'bird cages' of resistors, all with merit but somewhat lacking. Getting hold of non-inductive carbon composition resistors to build the latter are harder to find nowadays and somewhat expensive.

A cheaper and more elegant solution is as follows.....

Search eBay for "RF Termination Resistors".

This should herald plenty of results for Hybrid RF microwave termination resistors at a cost of approx. £3 to £6 each.
(These are surplus items and I believe used in mobile phone cell towers, I haven't bought a duff unit yet.)

Then check out the following link for an example build :-

RF Dummy Load DIY

Nothing more simple than one of these resistors, RF socket and a heatsink

I've built a couple myself, a 100w unit and a 250 watt unit the first built on a heatsink and the second on an extruded aluminium case. Both work faultlessly.

You can of course purchase several of these resistors and install them as parallel/series circuits to yield higher wattages. The old mineral oil filled can will help with cooling or build on a larger heatsink.


TIP :-

The silver tab for connecting to these hybrid resistors are quite delicate, make sure they are connected via a mechanically sound connection. Don't be tempted to just solder on a lead as they will break, typically right at the component body! Go on, ask me how I know

Also, don't be tempted to run any power through them without being connected to a decent heatsink. They will get hot very quickly and blow! Use good mechanical clamping and don't forget the old heatsink compound.


Helped me out discovering this, I hope it helps you.


All the best,
Victor

Totally agree. Built my own one. Which works great.

As admin cant be bothered to put my contribution to making a dummy load which I ask for to be put in this section. 
The Salt Water Dummy Load,I'll post it myself this   dummy load will cost you nearly nothing because you use stuff to make it you'll find in your house the only technical bit is using a soldering iron  I have made a few of these with good results anyway here is a video by Gary (Ofplanet) who is a old member on here and I want him to get the credit
https://youtu.be/u0qfSMWyjaw


Some history about Salt Water dummy loads that have been about for years before the modern ones
https://kv5r.com/ham-radio/2018-projects/salt-water-dummy-load/

hi guys. 

It may be helpful for someone to explain why having and using a dummy load is useful as again it not a regular conversation especially to newcomers to the hobby!

I'm uncertain, if not perplexed by the last couple of responses to this posting, but will do my best to resolve or at least understand them. (If not only for me but maybe others also.)


Martin,
You are certainly free to make any posting on the forum of your own regard for almost any subject you wish. (Obviously within forum rule boundaries.) As you have added another resource for a DIY approach to a dummy load it is a more than valid input. You could also if you wished place your resource in a posting of your own with titling specific to a salt water dummy load. It's totally up to you.

I don't understand the "as admin can't be bothered" aspect of your posting. I certainly haven't received any peronal request and I'm unaware of other admin receiving such a request but I'll double check for you. However, as mentioned you are free to make any posting of your own.

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John,
There may very well be people, or as you mention newcomers that do not know what a dummy load is. Again, as I have mentioned to Martin you are more than free to make such a posting of your own with that regard if you wish. I know that for myself when I come across a phrasing, abbreviation or other such that a quick search with Google or other search engine usually heralds answers to my query. Indeed searching for "dummy load" certainly gives many results on this particular subject.

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This forum is totally reliant on the input made from it's members and I believe a good resource for anyone involved or interested in radio.
If you feel it would benefit from specific information then you are totally free to add information to it. Whenever I have had the free time I certainly add postings that may, (or maybe not ), be of interest to other members and add to the wealth of knowledge here.

That was certainly my intention here, sharing a resource that might be of benefit to others and definitely helped me. If it's a known resource someone may confirm it, (as occured here), ask further questions, or even make further suggestions to add to the knowledge. All good stuff I'm sure you'll agree.


Anyway, I hope that sheds a bit more light.

All the best,
Victor

Victor if you look at one of my post in the Antenna section its says " Admin please feel to post this in the Information section but give the video maker Gary (Offplanet)the credit" the reason I ask Admin to do it was when I posted the Q code list Lee put it in the info section so I thought it was up to Admin to do it ,but also I got a bit of a impression that some thought I was talking cr*p and was more interested in making ones with diodes and heatsinks which cost money ,my info cost next to nothing and was use by radio operators (not just hams)years ago in fact it's common physics and not really electrical or radio .

Info on What a Dummy Load is used for 
Sorry it's a Google link I'm not very good at explaining in technical terms 

https://en.wikipedia.org/wiki/Dummy_load

Ah, OK Martin, it makes more sense now.

I thought you had specifically asked admin to make a posting maybe via a PM or something and hence my confusion. Easily missed if it was just on the fly in a posting. 

I just had a quick scout through the forum just now and found your posting, I had remarked on the unusual idea but obviously missed your intention. Still, as I said you are free to make your own posting. I couldn't find any reason however to make suggestion that anyone thought your input was a poor one though?


The reason for making my posting was to share a solution I had found for a dummy load. The resistors were cheap, the heatsinks free from discarded items and it works from DC to 3GHz so useful for the many frequencies Hams experience. No less worthy, indifferent, hard work or expensive than your input.

Anyway, glad we got that cleared up

All the best,
Victor

Hi Victor. 
In response t your comment. I totally agree with members making contributions on the forum. We agree that it is that that will keep it alive. 
Also Keeping it alive is that it’s a place for discussion and GOOD information on subjects and items that you could look up google responses and be flooded with a whole page or more of good, bad or indifferent comments . 
So having somewhere that you can trust giving you the simple facts that can be understood and found easily is a good thing. 
That’s why I come here and read up on headings of interest. JMO

Oh and I don’t know what a dummy load is.
 I didn’t want to admit it so I’m sure there’s others out there too!

This all came from the picture i put up and a joke after the post lol.
But some good info has come about from it that might save people a few bob.
Regarding the joke i will have a 500w Bird dummy load to use when the heatsink arrives to fix it to.
Have a look Victor what do you thing i have a pl adapter on it and it's still at 50ohm.  (£4.20 on the bay)...

Hi Alan,

Bit of a bargain that Bird terminator you got there. I do like a bargain even when it's someone else's bargain!

Got to admit I wasn't part of the original discussion so missed something(?) They might have added me to the admin team but it didn't come with omnipresence

Anyway, if even one person got something useful out of it all, then it's worth it.


You seem fair old setting up there Alan, fixing radios and expanding the test gear! All good to see.

All the best,
Victor

[size=46]Just warning beware this style and specification dummy load from a reprital cb shop or ebay seller go for about £25/£35 so when my mate and I saw them for £15 on ebay new and aUK seller thought we'll get a couple, they turned up guess what ,from China ,so my mate decided to test his one before use, well it wasn't even 50ohms like its suppose to be and was suppose to handle 30w it could only handle 5w when I checked mine it wasn't even connected inside so basically if we never check we would damaged our equipment, so if it looks a bargain beware [/size]
[size=46]here are the photos of mine [/size]
[size=46]
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Victor
I posted a picture of my SWR and somebody said i bet there is a dummy load some ware as a joke.
The Bird one i have only arrived yesterday and waiting for the 6x2x1 lump of aluminium to be delivered for the heatsink.
Did give it a quick try and it does work well but was starting to get warm after 5/10 seconds but well pleased with my bargain don't normally get them as i sit thinking for too long lol.
It's got a N-type to pl259 and a patch lead on it at the moment but still on 50ohm but it will be sorted out when the bit's turn up.
The funny look's have started from the wife now with this kit coming in aerial analyser came Wednesday 

I made my own 50ohm dummy load using readily available parts from CPC. I used a metal alloy box which was a bit small but a bit of ingenuity made it fit. The metal box helps with any heat build up. Coming from an electrical background kind of helped. 2x 100ohm 100watt panel mount resistors wired in parallel. Using 1.5mm sq electrical cable. All materials cost about £30. 
You could probably buy one for the rhe same money but where's the fun in that, plus it keeps you away from the other half
I would have added some photos but i don't seem to have an icon to add any

Well this was my attempt at building a dummy load. Works a treat.