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50 Ohm Dummy Load DIY

Joined: June 1st, 2016, 11:33 pm

May 2nd, 2018, 11:31 am #1

Afternoon all. Some advice needed please. I have made a dummy load from stuff laying around at work. I will attach a photo later when I get home if need be. I have 2x 48 ohm resistors in series and have another pair the same so they should total 96ohm each pair. Have wired them in parallel to a pl259 and now have 48 ohms at the plug which is what I want. However, when I use the dummy load on the SWR meter it reads 3:1. Have used it on all 3 of my meters and they all read roughly the same. The resistors are low wattage each so that's why I doubled them up.
I know I can buy a dummy load for not too much money but I thought I would have a go at making one and I'm just intrigued as to why this one doesn't work properly.
Many thanks as always.
Gary.
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Ste
Joined: May 23rd, 2017, 11:44 am

May 2nd, 2018, 2:20 pm #2

unless the resistors are carbon film or carbon composite then they will look like inductors at radio frequency dure to the way they are constructed. this will be causing the SWR to be out even though they measure correctly at DC

Im intending to use 20 of these in parallel

https://uk.rs-online.com/web/p/through- ... s/7078861/

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Joined: June 1st, 2016, 11:33 pm

May 2nd, 2018, 3:11 pm #3

Cool. Thanks for that. Just couldn't work it out.
Regards.
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Ste
Joined: May 23rd, 2017, 11:44 am

May 3rd, 2018, 6:31 am #4

Speidy wrote:Cool. Thanks for that. Just couldn't work it out.
Regards.
practical constructional article here

http://www.americanradiohistory.com/Arc ... 3%2001.pdf
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Ste
Joined: May 23rd, 2017, 11:44 am

May 10th, 2018, 8:03 am #5

et voila. knocked this together last night. just need a golden syrup tin now.
dummy_load_3.jpg
dummy_load_2.jpg
dummy_load_1.jpg
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Joined: June 1st, 2016, 11:33 pm

May 10th, 2018, 9:27 am #6

That's a thing of beauty.
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Joined: February 23rd, 2018, 11:18 pm

May 10th, 2018, 2:20 pm #7

Is that 20 x 1k resistors in parallel ? Whatever it is it looks very neat.

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Joined: February 23rd, 2018, 11:18 pm

May 10th, 2018, 2:27 pm #8

In a pinch you could use a ctx special https://youtu.be/u0qfSMWyjaw
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Joined: April 23rd, 2011, 5:12 pm

May 10th, 2018, 4:24 pm #9

Ste wrote:et voila. knocked this together last night. just need a golden syrup tin now.
I made this just after Fred's design was first published. Mine has the red LED in the lid to indicate power applied and used two brass discs drilled in line with resistors between them. I went on to build his ZL special two metre beam and the Slim Jim also for two metres. (From the articles in the original Out Of Thin Air). I greatly admired his simplicity of design and still going well today. Rated at 50watts continuous, 100watts (5 minutes) 200watts 2 minutes. Whole assembly is completely covered with silica sand when upright and is sealed in a 1lb Lyle's Golden Syrup tin with lid soldered securely on. I wish that I had actually painted the tin before use and not used (now scruffy) white stick on labels to indicate the ratings of the unit. One of those "Get around to it eventually) projects.
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Ste
Joined: May 23rd, 2017, 11:44 am

May 11th, 2018, 6:54 am #10

Roy2812 wrote:
Ste wrote:et voila. knocked this together last night. just need a golden syrup tin now.
I made this just after Fred's design was first published. Mine has the red LED in the lid to indicate power applied and used two brass discs drilled in line with resistors between them. I went on to build his ZL special two metre beam and the Slim Jim also for two metres. (From the articles in the original Out Of Thin Air). I greatly admired his simplicity of design and still going well today. Rated at 50watts continuous, 100watts (5 minutes) 200watts 2 minutes. Whole assembly is completely covered with silica sand when upright and is sealed in a 1lb Lyle's Golden Syrup tin with lid soldered securely on. I wish that I had actually painted the tin before use and not used (now scruffy) white stick on labels to indicate the ratings of the unit. One of those "Get around to it eventually) projects.
Nice one Roy. Yes he did some nice Antenna designs. Im going to have another go at the 144Mhz Ring Base antenna, Annoyingly I still had the base of one I made years ago until the last garage clearout. Bought a tin of syrup last night, so Its flapjacks galore until its gone haha
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