Fwd: [Premium-Rx] More Diversity Reception Approaches

[w3sz]

Hello, All!

This very interesting discussion has caused me to make my first [or nearly first]
posting to the group.  I apologize if what I am about to say is not on this topic,
but I think it is and that it might be helpful.

My interest is in weak signal VHF/UHF/microwave reception.  I particularly enjoy 144
MHz EME.  My interest in this list is a result of these interests.

On 144 MHz EME one of the problems we face is rotation of the polarization of the
received signal.  There is a predictable, geometric rotation that can be calculated
based on the positions of the sending and receiving stations and the position of the
moon.  There is an unpredictable atmospheric rotation called 'Faraday' rotation.  If
one doesn't have control of the polarization angle of the received signal, one can
be
'locked out' and hear no signal.

One way of combating this is to have both vertically and horizontally polarized yagi
elements.  One can switch between the two and be 'close' to the correct polarization
much of the time.

Leif Asbrink, SM5BSZ, has written a piece of software called Linrad which I have
been
using for a bit more than 3 years.  It will simultaneously receive signals from the
two sets of elements and in realtime calculate the correct polarization angle so
that
the maximum signal is received, and put this out on the screen and more importantly
to the headphones.  

I have this set up with two homebrew 144 MHz front ends that downvert the signal to
2.5 MHz. An I/Q mixer-downverter then converts this all to audio and gives a 96 KHz
wide bandsegment on the screen.  Clicking on a signal displayed in this 96 KHz
bandwidth causes it to be processed and sent to the headphones.

This was designed initially for 144 MHz EME and control of polarization angle
reception, with ANY received angle being optimally detected, any two signals can be
fed into the channels and so I would think that diversity reception could thereby be
achieved.  What I am doing with the program is just a special case of diversity
reception, where one channel has vertical elements and the other horizontal
elements.

However, I believe absolute equality of the frequency of the LO's and VFO's or
synthesizers, and of PHASE of these is essential I believe [at least it is for the
purpose I use it for;  I am not sure about how critical this would be if it is used
for HF diversity reception].  This would be difficult to achieve with two separate
radios, one fed to each channel.  I achieve it here by using GPS-controlled PTS
synthesizers that are phase-locked for the two different channels as the LO's.  

Here, with the setup I am using, I could implement an HF diversity receive system by
just unhooking my homebrew front ends from the 144 MHz preamps and hooking the front
ends instead to two HF antennas, and dialing in alternate LO frequencies.

Alternatively, one could make a simple start at diversity reception with no
additional hardware by taking the audio outputs from two receivers, feeding them
into
Linrad, and seeing what happens.

The links to Leif's pages on Linrad are:

http://www.antennspecialisten.com/~sm5bsz/linuxdsp/linrad.htm
http://www.antennspecialisten.com/~sm5bsz/linuxdsp/linroot.htm

I have some notes on Leif's software and my experiences with it at:

http://www.qsl.net/w3sz/DUBUSLinrad2002.pdf
http://www.qsl.net/w3sz/w3szdspnew.htm#linrad
http://www.qsl.net/w3sz/SM5BSZ1.htm
with some other links taking off from
http://www.qsl.net/w3sz/start.htm

Comments, if any, welcome either directly or over the reflector.

73,

Roger Rehr
W3SZ



----- Original Message Follows -----
> Many thanks to Richard for uploading Capt. Lee's wonderful article on 
> Diversity Reception. I remember the first time that I read it in 1964 or 
> 5.... I've lusted after such a set-up ever since and I've enjoyed this 
> exchange.  I'm not sure that it is off-topic, either... Its about one way 
> to use Premium Receivers.
> 
> Some of you might be interested in a very non-original article that I wrote 
> some years ago about an audio switching arrangement that facilitates yet 
> another type of Diversity Reception... "Receiver Diversity Reception." 
The 
> article is currently posted on the dxing.info site' Equipment page under 
> "Audio Switching Network"  The URL of the entire equipment article 
> collection is   http://www.dxing.info/equipment/



73,
Roger Rehr
W3SZ
FN20ah
http://www.qsl.net/w3sz




73,
Roger Rehr
W3SZ
FN20ah
http://www.qsl.net/w3sz