Re: diversity receive antennas

Posted by Jack Smith-6 on Jan 09, 2012; 12:14am
URL: http://elecraft.85.s1.nabble.com/diversity-receive-antennas-tp7165975p7166134.html

The chief driver of diversity gain is antenna separation. The usual
recommendation is 10 wavelengths separation for low correlation fading.
That's impractical for most amateur installations, particularly on the
lower frequency bands where diversity gain may be the most desired.

I've made some measurements using simultaneous capture of signal levels
with  two identical spectrum analyzers and  two antennas that suggest
around 3 dB diversity gain is achievable with ~0.5 wavelengths
separation, but I'm hesitant to put too much faith in that figure as it
used two rather different antennas - an 80 meter band inverted vee and
one of my Z1501 active antennas.  Nonetheless, the data clearly showed
increasing diversity gain with increasing antenna separation measured in
terms of wavelengths over the frequency range 760 KHz - 15 MHz, with
some diversity gain possible with tiny separation - 0.1 wavelength. Not
a lot of gain, but enough to measure after post processing analysis.

Although about 3 dB diversity gain was achieved around 0.5 wavelength
separation, that does not mean a 3 dB improvement at all times. Rather,
that's the mean of the gain probability distribution. A certain
percentage of the time, the gain may be 0 dB and for a certain
percentage of the time it may be 6 or 8 dB or more. The percentage of
time 6 or 8 dB diversity gain is seen with 0.5 wavelength separation is,
of course, small, with smaller gains being more frequent.

Jack K8ZOA


On 1/8/2012 6:48 PM, Don Wilhelm wrote:

> Don,
>
> You should get a variety of answers - there are some using dedicated
> receive antennas, and there are others who are using two transmit
> antennas.  It depends on what they have available.
>
> It is nice to have one antenna with vertical polarization and another
> with horizontal polarization, but two antennas separated by some
> distance can work too.  Use what you have.
>
> If you only have 2 antennas, I suggest that you connect the subRX to use
> the Non-Transmit antenna connected to the KAT3.  To use that, you will
> need to connect the TMP cable between the KAT3 and the SubRX AUX antenna
> input.
>
> 73,
> Don W3FPR
>
> On 1/8/2012 5:25 PM, [hidden email] wrote:
>> What do folks use for diversity receive antennas.
>>
>> Do you have a dedicated receive antenna or just a different TX antenna
>> from the antenna farm.
>>
>> I am looking for ideas on what to do next as I have the big loop and the
>> dipole.
>>
>> Right now I have no idea on what I should do next.
>>
>> Thanks
>> Don
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html