[Elecraft] Diversity Reception

[Edward R Cole]

Inserted comments, below:
----------
Date: Mon, 3 Aug 2015 21:32:33 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Diversity Reception
Message-ID: <55C04061.8000905 at audiosystemsgroup.com>
Content-Type: text/plain; charset=windows-1252; format=flowed

On Mon,8/3/2015 8:41 PM, Edward R Cole wrote:
 > However it is not always bad for the two diversity channels to be
 > combined for best signal.  The example is digital signals which the
 > human brain cannot process.  The example was given of using two
 > antennas of differing polarity for HF.

Combining, yes -- into different inputs of the analysis system. Again,
when signals combine IN THE SAME SIGNAL CHANNEL (emphasis added)
differences in the time/phase response of the two signal paths can cause
destructive interference which degrades decoding.

# Yes, simple combining of RF signal would result in such effects.

OTOH, in a sophisticated decoding system, there's certainly nothing
wrong with bring both signals in on separate inputs, then combining
them, or choosing the best signal, or even processing the signals to
enhance readability. But ONLY combining them on a single electrical
channel is a bad idea.

# Our dual-pol adaptive eme system is done in digital domain with DSP 
where channel amplitude and phase angle can be separated for 
re-combination using sw which accomplishes vector addition of the 
signal to produce display of polarity angle and constructive addition 
of signals.  Both Linrad and MAP65 can perform these computations.

One of my neighbors (near Santa Cruz) has a VERY interesting UHF
repeater system. It's multi-site(five sites going on six),voted (meaning
that the RX with the best signal is transmitted), and simulcast (all
sites transmit at the same time). To make this work, Bboth audio and RF
are synchronized to the Hz using a GPS reference and some really
innovative use of low cost audio and networking gear. If you're
interested, look at wb6ece.org, especially the Technical Info page,
where there's video and audio of a talk that KA6SQG did at Pacificon
about his system (WB6ECE is his dad's call). The audio is not well
recorded, so you'll need headphones for good copy.

73, Jim K9YC

# My only exposure was with Motorola voting systems for commercial FM 
2-way communications.  I did not do much with such here in AK.  I 
believe one ham 2m repeating system used a couple voted satellite 
receivers. Occasionally they would hunt a little causing a chopped signal.

73, Ed





73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com