Posted by
Guy, K2AV on
Jan 09, 2012; 2:46am
URL: http://elecraft.85.s1.nabble.com/diversity-receive-antennas-tp7165975p7166358.html
A lot of answers to diversity questions seem to be based on using diversity
to feed electrical devices that combine signals before they are heard.
This was most often done to defeat signal level fading. Some very accurate
technical answers to that are heard based on 100% electronic process.
However, there is a different KIND of diversity, where one signal is fed to
the left ear, without any correction, and the same signal from a different
antenna and identical phase-locked RX is fed to the right ear, without any
correction. This allows the brain to decide what is different between the
two signals, frequently producing a sense of stereophonic aural spatiality.
This latter is far more useful for SSB and CW reception. Frequent
descriptions of this have the incoming sky wave noise spread around the
audio horizon, while the discrete signals come from a single point on the
audio horizon. There are some number of other effects, but always seeming
to make difficult signals easier to copy.
With this latter kind of useful diversity, a NE beverage in one ear and a
NW beverage in the other can produce considerable improvements in weak
signal copy. This is a completely different diversity strategy than
hearing multiple sources to reduce or eliminate fading.
73, Guy.
On Sun, Jan 8, 2012 at 7:14 PM, Jack Smith <
[hidden email]> wrote:
> 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
> >>
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