[RFI] impedance mismatching in coax

Aaron Kreider aaron at campusactivism.org
Wed Dec 28 16:13:31 EST 2016

There wasn't any ground.  So I should have one of those (though in my 
city experience, a ground hasn't helped).  I'll probably build a better 
beverage (and terminate it) or KAZ antenna eventually.   The soil is rocky.

Goal is to receive MW stations, and LW as a secondary objective. Length 
was 500-1000 feet (I was wandering around in the woods at dusk - so hard 
to say).


On 12/28/2016 3:58 PM, donovanf at starpower.net wrote:
> Jim and Aaron,
> If you measure the shield isolation of a 1:1 transformer you'll
> discover -- contrary to popular belief -- that it provides only a
> modest amount of common mode rejection. K9YC's common
> mode chokes are vastly superior.
> Aaron never explicitly mentioned the frequency range over
> which he intends to operate his Beverageor any of the details
> (length, nature of the ground system, etc) for his temporary/quick
> Beverage.
> 73
> Frank
> w3LPL
> ----- Original Message -----
> From: "JW via RFI" <rfi at contesting.com>
> To: "Aaron Kreider" <aaron at campusactivism.org>, rfi at contesting.com
> Sent: Wednesday, December 28, 2016 8:46:10 PM
> Subject: Re: [RFI] impedance mismatching in coax
> Aaron,
> I found the better option in my case was a 1:1 flux coupled transformer using a ferrite core placed at the *receiver* end of the coax feedline.
> Background: I had noise up the wazoo before putting the 1:1 xfmr in the shack just before the receiver used on a 1/2 height K9AY loop placed in my city-lot-sized front yard. With the 1:1 xfmr I could actually see 60 kHz WWVB and the WSPR stations the others were seeing on 475 kHz.
> I think I used what I had on hand to wind the xfmer, a couple of large #43 beads and 3 turns primary and also 3 turns secondary. Was it optimum? Probably not, but I was at the point where I had to try something, and I got a good measure of positive results.
> Good luck.
> Jim WB5WPA
> From: Aaron Kreider <aaron at campusactivism.org>
> To: rfi at contesting.com
> Sent: Wednesday, December 28, 2016 12:02 PM
> Subject: [RFI] impedance mismatching in coax
> Over Christmas I built a temporary/quick beverage antenna in a rural
> area, but it had a very high noise level. I had chokes on everything
> which helped, but as I hadn't a lot of planning - I ended up connecting
> two pieces of coax together with 50 ohm and 75 ohm reactance.
> Would this impedance mismatch cause any problems with the Type 43 toroids?
> If not, then I'm guessing I wasn't far enough away from the house (50-75
> feet away), and/or the house had a very dirty AC power. The location was
> perhaps 20-30 acres - so I could get further away from the house and
> electrical lines.
> The noise level at 500 khz was around 20-30 uV and below 100 khz there
> were spikes up to S9 + 40 db. It was pretty clean above 3-4 mhz (so
> this also points to the toroids working better at higher frequencies).
> Aaron

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