[Elecraft] Dummy loads for dummies

Tue Dec 27 18:23:46 EST 2016

For parts, digikey.com and mouser.com are good friends. No minimum order, great prices and huge selection. 

You've gotten several suggestions for a good dummy load. And I concur with the others, those wire-wound resistors might be 50 ohms but their reactance may almost anything and dependent upon frequency. One of the original "Elecrafter Field Testers" and "F.O.W." - friend of Wayne (Burdick) - was Tom Hammond, N0SS, no sadly an S.K. But his web site has been maintained and it contains a great low-cost dummy load design:

http://www.mmccs.com/mmarc/n0ss/dl_30w_hf-uhf.pdf

You might enjoy looking around the web site for more KX1 info and QRP info in general:

http://www.mmccs.com/mmarc/n0ss/

Coaxial cable is every much as low loss as open wire line when the SWR is not too high. The difference in applying them is that the inherently higher-impedance of ladder line makes it much easier to keep the SWR on the line low enough to avoid excessive loss. For example, a hunk of wire between 50 and 100 feet long strung up in the air and fed at its center will show an impedance of about 4,000 ohms at the frequency at which it is 1/2 wavelength long and perhaps as low as 40 ohms on 80 or 160 meters. With open wire line at about 400 ohms impedance, you will find an SWR of up to 10:1 on the feed line, generally much less. With 50 ohm coax, the SWR will range as high as 80:1 or more.

Have fun. At my shack, simple and cheap is great fun! 

73, Ron AC7AC 

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Paul C
Sent: Tuesday, December 27, 2016 12:23 PM
To: Walter Underwood; elecraft at mailman.qth.net
Subject: Re: [Elecraft] Dummy loads for dummies

Ok, I won't be using these resistors after all.  Thanks for setting me straight. 

It seems tuff to get going in QRP.  I thought I'd roll my own when possible.  I am trying to keep things simple and economical, the QRP spirit.

Here's another naive idea of mine:  I'm planning to use ladder line too.  Now I'm waiting for the other shoe to drop, when I realize coax will be my only practical choice.

Paul KG5KXG

-----Original Message-----
From: "Walter Underwood" <wunder at wunderwood.org>
Sent: ‎12/‎27/‎2016 1:45 PM
To: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Dummy loads for dummies

Ah, yes, bricks. Like these?

https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack# <https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack#>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 27, 2016, at 11:42 AM, Vic Rosenthal <k2vco.vic at gmail.com> wrote:
> 
> They are undoubtedly wire-wound resistors and will have too much inductance to work well as a dummy load. The resistance is fine. If you have an SWR meter, check it with that. SWR below about 1.5 would mean it is usable. It might be OK on 160 or 80 meters but not on higher bands.
> 
> Vic 4X6GP
> 
>> On 27 Dec 2016, at 16:43, Paul C <paulc22 at sbcglobal.net> wrote:
>> 
>> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>> 
>> Paul KG5KXG
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