Topband: E51D Oct 1

[Tim Duffy]

Here is a great high common mode impedance choke that I use just as George
explains. At the beginning and end of the feedline to all RX antennas.

https://www.dxengineering.com/parts/dxe-rxfc-75

73
Tim K3LR

-----Original Message-----
From: Topband [mailto:topband-bounces+k3lr=k3lr.com at contesting.com] On
Behalf Of GEORGE WALLNER
Sent: Thursday, October 3, 2024 9:43 PM
To: W7TMT - Patrick; ws6x.ars at gmail.com; topband at contesting.com
Subject: Re: Topband: E51D Oct 1

Hi Patrick,
This is a custom unit that I built. While this version would be very 
difficult to reproduce, there are some commercial pre-amps that come close. 
Specifically, the DX engineering SV-BF-99X5 by KD9SV, (Just set the gain to 
20 dB. Don't bother with higher gain as the noise figure gets worse.) In my 
case, I put the pre-amp into a small Pelican case along with a bias T (100 
nF series C and a100 uH and a 47 uH inductor in series.) I have also added a

GND terminal to the line end (to output side that goes to the receiver) 
which, in combination with a choke (#31 core with 8 turns of coax) ensures 
that noise travelling on the outside of the coax does couple into the 
antenna. Whether you use 50 Ohms and 75 Ohms coax is entirely up to you. 
Just make sure the connectors are good and well sealed against moisture.

I you want to reproduce my pre-amp, I am happy share the circuit diagram, 
but even I would not try do it again!

GL and LMKO if you need more info.
73,
George

On Thu, 3 Oct 2024 23:26:30 +0000 W7TMT - Patrick  wrote:
>
>
>George,
>
>If you have a moment a few more details about the feed-point amplifier
would be appreciated. Is this a custom unit or an of-the-shelf commercial
unit please?
>
>Thanks for your time. 
>
>Patrick, W7TMT 
>
>
>
>
>From: Topband <topband-bounces+w7tmt=outlook.com at contesting.com> on behalf
of GEORGE WALLNER <aa7jv at atlanticbb.net>Sent: Wednesday, October 2, 2024
7:55:20 PMTo: ws6x.ars at gmail.com <ws6x.ars at gmail.com>;
topband at contesting.com <topband at contesting.com>Subject: Re: Topband: E51D
Oct 1
> 
>
>
>Thank you Wes, but it wasn't my "ears" (which are not what they are used
tobe) but a new RX antenna and a very low noise pre-amplifier, that we
installed yesterday morning. Your signal was an easy copy with this new
antenna. There was no trace of it on the TX antenna! (You also set your
frequency well: a couple of hundred Hertz away from the other callers but
still withing the RX passband.)There is a timely thread going on about a
"Low Frequency RX Antenna". The antenna we installed yesterday is a single
support variant of this VE3DO loop, which is essentially a delta loop. This
type of antenna is easy to install and gives you an RDF that is just a few
of dB-s shy of a small Beverage, but at a much lower gain. The key is a low
noise amplifier located at the antenna. This is a must in almost all
situations. The amp is remote not to overcome the coax losses (which it
does), but to ensure
that amplification takes place before noise is introduced into the RX 
system. We have a single RIB on a small cay with two Honda 22i generators. 
Like most temporary installations, grounding is less then perfect and some 
noise couples into the RX circuit. A low noise pre-amp at the antenna, turns

a -30 dBi RX antenna into a -10 dBi RX antenna with an RDF of 7 dB. That is 
sufficient tooverpower the noise that inevitably gets into the receiver.I 
will be on TB again tonight.73,George,E51DPS: You can easily expand this 
antenna to cover four directions by adding a second loop on the same support

at 90 degrees, and use switchable transformers to change directions.On Wed, 
2 Oct 2024 11:12:43 -0400  wrote:>As a tribute to George's incredible ears 
on E5-N, this morning, at 1107 UTC,>just before local SR, I worked E51D QRP,

using a "nothing special" Inv-L.>This is from Northwest Rockingham County,
VA, FM08. The signal was solid>copy, averaging around S7. Signal strength 
was not quite as loud as 2 days>prior, when peaks reached nearly S9.>Oddly, 
yesterday, morning, on FT8, I couldn't work E51D with a kW!>Thanks, 
George.>Jim - WS6X _________________>Searchable Archives: 
>http://www.contesting.com/_topband> - Topband 
Reflector>_________________Searchable Archives: 
http://www.contesting.com/_topband - Topband Reflector
>

_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector