Hi Roger,
Your loft-mounted small receiving loop is working well, congratulations!
Your somewhat reduced null depth at night is caused by horizontally
polarized signals leaking into the side of your loop. That can
be improved only by locating it near the ground
Well done OM!
73
Frank
W3LPL
----- Original Message -----
From: "Roger Kennedy" <roger@wessexproductions.co.uk>
To: "topband" <topband@contesting.com>
Sent: Tuesday, May 23, 2023 4:07:27 PM
Subject: Re: Topband: Loop on Ground receiving antenna.
Many thanks for the replies (some direct) . . . it seems the LOG IS rubbish.
And Frank, considering what you say, my 6ft Vertical Loop in the Loft works
surprisingly well. It's obviously NOT near the ground, and there is mains
wiring running along the floor underneath it (to the lights in the ceiling
below).
Despite any shortcomings, having set the Preamp Gain so that a local signal
in the right direction is the same strength as on my Dipole, the noise is 6
- 10dB lower than on my Dipole. It also has a BIG null at right angles - a
local to the South of me is 30dB weaker on the Loop!
I can certainly tell that it works as a Vertical antenna, as not only the
strength but also the sound of signals changes a lot, especially if they are
around 1000 miles away (where normally a Vertical would be better).
Interestingly real DX signals (over 3000 miles) are rarely any stronger on
the Loop . . . which confirms my suspicion that DX on 160m is rarely Low
Angle! (based on reports I get from my Dipole Tx antenna too)
For anyone else who doesn't have room for a Beverage or even K9AY, here's
details again of my 160m Receiving Loop:
http://rogerkennedy.co.uk/g3yro/160mrxloop.htm
Roger G3YRO
-----Original Message-----
From: Frank W3LPL [mailto:donovanf@starpower.net]
Sent: 23 May 2023 16:40
To: topband
Subject: Re: Topband: Loop on Ground receiving antenna.
Hi Roger,
Any 160 meter receiving antenna laying on conductive soil will have
extremely low RF output and you'll need at least 40 dB of preamp gain with
very low noise figure and you must take extreme measures to control common
mode currents. Antennas NEAR the ground perform dramatically better than
antennas ON the ground.
Vertically polarized small loops like your 6 foot loop must be installed
within about 7 feet of the ground, otherwise the two vertically polarized
deep nulls get washed out by horizontally polarized signals that are no
longer suppressed by ground proximity.
I hope you don't have a lot of wiring and other metallic structures in or
near your loft, otherwise your small loop doesn't have a prayer of working
at all. You also must take extreme measures to suppress common mode
currents when using a small loop.
What constraints must you take into consideration when selecting the
location for your receiving antennas?
73
Frank
W3LPL
----- Original Message -----
From: "Roger Kennedy" <roger@wessexproductions.co.uk>
To: "topband" <topband@contesting.com>
Sent: Tuesday, May 23, 2023 3:05:13 PM
Subject: Topband: Loop on Ground receiving antenna.
I just tried making a Loop on the Ground to see if it would be any lower
noise than my 6ft 160m Loop up in the loft.
I followed several people's suggested dimensions . . . so 15 feet each side,
feeding it in the middle of the side pointing West with a 450:50 ohm
transformer . . . And it's rubbish!
A local station (in the right direction) on my 6ft vertical loop in the loft
needs a 20dB preamp to bring him to the same level as on my Dipole (and the
noise is 6 to 10dB lower).
But on the LOG he was 30dB weaker, that's WITH the 20dB preamp! So the S/N
would be rubbish. Anyone else tried something similar on 160m?
Roger G3YRO
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