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@contesting.com>
To: "Aaron Kreider" <aaron@campusactivism.org>, rfi@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@campusactivism.org>
To: rfi@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
--
High resolution map of race and income --> JusticeMap.org
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