Topband: Diversity in CQ 160 contest

Sat Feb 5 10:05:31 PST 2011

I have pulled this thread from the Elecraft reflector as it has broad
application and seems to particularly specific to the topband audience.

The just past CQ 160 was my first 160 contest using diversity (K3) and an RX
antenna.

Using an extension of some successful experiences with BOG arrays I designed
for W0UCE, I used a pair of balanced, ungrounded electrical fullwave loops
on ground phased for the NE (LOG array ? :>)), and my TX antenna (3/8 wave
endfed L) .

I was (and remain) somewhat stunned by the degree that the noise from BOTH
ant is spread around the "audio horizon" in diversity, while the CW (from
either or both antennas) remains discrete in some "direction" on the audio
horizon even if that direction has a lot of variance.  I have a few
persistent weak birdies which are convenient for s/n comparison, which prove
that directional discrimination IS in effect. My favorite one at 1816.67,
daytime, shows a steady and persistent 13 dB improvement in s/n on the LOGs
over the L on Spectrogram.

My RX to EU has gone from being afraid to call CQ QRO because of simply not
hearing people calling me on the L, to being as sensitive or more sensitive
as anyone in the area I have been able to compare with lacking JI/ZV/LPL
style beverage arrays.

The real (and unexplained) bonus is what the pair under diversity has done
for hearing off the TX antenna.  Case in point, VP8ORK.  Not copiable on
either separately, an uncopiable STRONGER in the noise on the TX vs
uncopiable in the noise on the LOGs.  With diversity VP8ORK is well in the
clear, as if some broad noise cancellation was in effect.  Certainly more
than I had expected.  Going from a 129 on EITHER separately to a very
clearly heard 549 on BOTH in diversity.

To be complete, the night was unusually clear of QRN (will we ever have
quiet winters again?) and it was the "hissy" kind of 160 ambient noise
controlling.

This clarity was also in effect for the CQ 160.  I was running 100 watts (a
long story) SOLP for the contest.  At one point a UT5 came on my run
frequency, up about 80 Hz.  I was able to hear him well for over two hours,
but doubt he heard me. About half the time I could clearly hear the stations
calling him. The diversity and 80 Hz clearly separated stations from the US
calling me and stations from EU calling him, making his presence on the
frequency a non-issue.

The root of diversity's extraordinary ability to spread the noise in my
circumstance seems to be a qualitative difference between the noise on the
two. Just to the ear, the LOG noise is a lot more hissy and missing a lot of
the harshness of the noise on the L.  The LOG does reject the buzzy stuff on
the L that I hear during the day, but that buzz seems to be covered by the
nighttime ambient noise on the L so the buzz does not control the noise at
night on the L. But the difference in the "harshness" remains at night.

In any event, the difference between the two creates a perceived spatial
spread that vastly improves a discreet CQ signal on the L, even one that is
poorly heard on the NE phased LOGs.

To this point all the talk on RX antennas has had to do with brute force
improvement of signal to noise in a single signal stream, and I do not
question the results at stations the likes of W8JI, W4ZV, W3LPL et al.  But
these power plants are not feasible at most QTH.  I am wondering if
diversity RX can improve urban reception significantly with a single on
ground RX antenna whose MAIN purpose is to provide "anti-noise" for
diversity spread of noise in a diversity RX, any directional improvement in
same appreciated, but not the only main course item on the menu.

In the 160 contest I also used a single wire 5/16 wave folded counterpoise
which is a +33, -33 foot replacement for inevitably lossy faint imitations
of properly dense well done radial systems.  The LOG's are ROUGHLY 70x70
loops on the ground, which can be notched into the ground like invisible
fences for dogs.  Smaller variants of these Ground Low Velocity Factor
antennas will be tried, including phased Dipoles On Ground, with some
space-saving bends to make a double DOG fit in a smaller footprint.

This CQ160 CW certainly was my personal best in a 160 contest, by far.
 Thanks to Elecraft for putting true diversity within my means.  Whether or
not these small lot techniques can put a competitive station on in a contest
is in your own evaluation of the contest scores.

But as of now IMHO, it appears that with the best L someone can get up into
their trees, a 5/16 FCP, some form of GLVF RX antenna that fits the property
as a source of "anti-noise" or even with a directionality bonus, and a K3
with a KRX3 for true diversity, one can make the SOLP class on 160 VERY
competitive from a lot that was heretofore considered too far gone for 160,
even if you have neighbors whose devices shut down when you key an amp.

73, Guy K2AV

On Sat, Feb 5, 2011 at 9:13 AM, Bill W4ZV <btippett at alum.mit.edu> wrote:

>
> NO9E wrote:
>
> > APF was different story for RUN. Turning on APF was too slow. Having an
> > option to switch XFIL and APF for CW only would be great. I guess
> software
> > APF toggle change via PF key may be good enough.
>
> I never used APF in the CQ 160 (who has time to tune in 5 Hz steps using
> SHIFT or 1 Hz steps using VFO?) but here's a good tip for casual operating
> from Wayne N6KR:
>
> Use Preset I and II to toggle APF On and Off more quickly.  You can also
> set
> different XFILs using the Presets.
>
> > Some gremlins got into N1MM here. Every so often, written callsigns would
> > disappear,  SPLIT would show up, and work frequency would change from
> 1820
> > to 18200. Reloading CONFIG would cure it. Not sure whether it was KUSB,
> RF
> > or Vista.
>
> I had a few problems like that but not sure it was N1MM.  I normally
> operate
> SPLIT on my run frequency so I can use the BIG VFO A knob to tune RX
> (leaving my TX fixed on VFO B).  Occasionally I noticed VFO B was not on my
> run frequency!  Could be I touched the VFO B knob (which is a good reminder
> to always LOCK VFO B when operating like this).
>
> If I was suddenly calling CQ on top of someone else, my apologies!
>
> 73,  Bill
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/P3-APF-and-diversity-in-CQ-160-contest-tp5995363p5995500.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>