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@contesting.com> on behalf of GEORGE WALLNER
<aa7jv@atlanticbb.net>Sent: Wednesday, October 2, 2024 7:55:20 PMTo: ws6x.ars@gmail.com
<ws6x.ars@gmail.com>; topband@contesting.com <topband@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:
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