[R-390] R-392 Performance on Loop antenna

Sun, 22 Jun 2003 12:20:22 +0100

Hi, Gregory, and thanks for your interest.

You are right theat the R-392 will work on 28vdc, but the extra volt or two
on the 'HT' improves sensitivity with only a minute reduction in noise
factor.

The  R-392 Heaters are fed from a 28 volt tap on the accumulator. This is
normal practice and is allowed by the Military in one of  the handbooks.

I charge my accumulator stack on cheap power at night and use it during the
day. It also serves to power my Collins 18S-4 100Watt AM rig!

The loop consists of 3 x 1 metre lengths of pipe, joined at right angles to
form a u shape.
The fourth side closes the U to make a square with a gap in one side with
two pieces of pipe about 0.45 metre each, again attached by right angle
elbows, so there is a gap in the centre of one side. Here I mount a 1000pF
airspaced variable Cap.

The coupling is done in coax and consists of a 1 metre length of coax
connected to a tee piece at one end, by a normally terminated coax plug.
 The other end is terninated (unusually) in a coax plug, but with the inner
of the coax cable connected to the outer body metalwork of its plug. This is
then returned to the second socket on the tee piece.
This forms a screened single turn pick up coil.

I used BNC coax fittings throughout.

I sweated a machine screw onto the rear of the tee piece and fixed it to a
plastic pipe clip.
I attached another pipe clip to the coax cable with a small plastic 'P'
clip.
Thus the pickup loop is supported by two points by clipping it onto the 15mm
copper pipe forming the main loop.

The third socket on the tee piece goes via a normal coax to the RX antenna
socket.

Theory says that the loop should be positioned opposite the capacitor arm of
the main loop. In practice I have found it makes no difference where it is
placed, except that the antenna is easier to handle if it is placed lower
down due to lower centre of gravity. I will re-test this findind in open
space away from metal objects to see if the theoretical prediction holds
where the field is more natural around the antenna.....need the field trip
for that one!

73

Pete
----- Original Message -----
From: "Gregory Mengell" <[email protected]>
To: "Peter Worrall" <[email protected]>
Sent: Saturday, June 21, 2003 6:04 PM
Subject: Re: [R-390] R-392 Performance on Loop antenna

> Hi Peter, I believe 28 volts is about max that the R 392 can take.Are you
> dropping down the voltage somehow or does yhe load of the R392 on your
suppy
> drop it to 28 volts? I have used them for more years than I remember with
> remarkable results.How did you match your loop to the radio?73 Gregory
> ----- Original Message -----
> From: "Peter Worrall" <[email protected]>
> To: "blw" <[email protected]>; <[email protected]>
> Sent: Saturday, June 21, 2003 9:50 AM
> Subject: [R-390] R-392 Performance on Loop antenna
>
>
> > I have been playing with a 1 metre square loop antenna soldered up from
> 15mm
> > water pipe lengths. I use a 1000pF cap to tune (it runs 2700 to 14500kc
> > barefoot) and I add a parallel pair of 1000pF 10kV caps to take it down
> into
> > top band.
> >
> > As the R-392 has been out to play with on the bench for a few weeks, and
I
> > am running it from a 30 vdc accumulator, I decided to try the loop on
the
> > r-392.
> >
> > The performance is astonishing!
> >
> > The loop delivers enough rf to overload the '392 on 4000 to 6000kc after
> > darkness has fallen. Performance is excellent over the entire range with
> > topband noise (a real problem here) reduced to very low levels. The
> > directivity and the e-wave noise immunity contribute to its performance
> and
> > off set the lower signal levels it delivers to the RX load.
> >
> > To anyone wishing to use HF receivers in a noisy or no-antenna
environment
> I
> > would recommend using loops they are easy to build and most effective
buck
> > (�) for dB. BTW there is no hi-Z amplifier between the loop and the
> > RX....just a screened single turn of coax and an inductive coupling
link.
> >
> > I will take the 392 out to a rural noise free location on batteries with
> the
> > loop to see what the performance under those conditions is like in the
> next
> > week or two. The results will  be posted later.
> >
> > 73
> >
> > Pete G4GJL
> >
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> >
>