Last week, for the ARRL DX CW contest, Sine/s53rm and I set for an
experiment - results might be of interest to a wider contesting community.
The main idea was to verify performance of the VDA antenna at the sea
front (Vertical Dipole with Reflector) in direct comparison with the
"regular BIG GUN setup" - at the same time and same micro location. Our
TeamC (TK0C) has almost 10 years of experience with VDAs (using them as
in-band antenna), but there is never enough time to make quality
performance comparison. So Sine/s53rm and I set for a direct competition
on a 10m band as SOSB10hp. S53RM operated station with two stacked
5el.yagis on top of the 400m a.s.l. hill with sloping terrain toward the
US. And where the terain hit the sea (7km from the hill top), I installed
a single VDA antenna at the sea shore (having wet feet during the high
tide). It was a field day style operation in a camp, working from a van,
50m coax to the antenna, SSPA outputting 1450W.
For the VDA at the sea front the radiation pattern is without unknowns;
10dBi of gain down to zero elevation. The 5-over-5 stack on the hill top
is not that straightforward as the sloping terrain is far from the model
used by the Terain Analayzer - in fact, the vertical radiation pattern
changes significantly when simulated between, let say, 310 and 315 azimuth
angle. Nevertheless, 8dB higher gain as compared to the VDA was expected.
The result is confusing at best. S50C made only 41 QSOs and one multiplier
more than me (836 vs. 795 QSO). For the first day we agreed to operate
"big gun" style (grab a QRG and call CQ). S50C finished with 491 QSOs (80
more than me), where first 40 were gained during the band opening, and the
second 40 during the band closing. We had the same number of multipliers
(49), but different were missing and jointy we logged 655 different
stations. I was monitoring the RBN reports all the time and S50C was
always 6dB to 16dB stronger (reports would come from the same skimmer at
the same time, so no fading contribution here). On Sunday, the conditions
improved, still the QSO difference diminished from 81 to 41. On Sunday
s53rm was mainly calling CQ (24 S&P QSOs), while I spent more time S&P as
no one would come to my CQ for minutes (61 S&P QSOs). The final QSO
difference was made on the west coast (Zone 3) stations (71 vs. 35). In a
joint LOG we have 1107 different calls (85 from Zone 3).
Now, 200km inland to the east and south east, another two stations
operated as SOUSB10hp, 9A3TR(@9A7A) and E70T(@E7DX). Both with similar
setup as S50C (7/7 and 5/5) over flat land. RBN reports show similar
signal strengths as for S50C (but different fading conditions - as
expected). If their S&P QSOs are removed, the total QSO count is 868 for
9A3TR and 905 for E70T. So if all of us would be just calling CQ, we would
made approximately the same number of QSOs (800-900).
But the 4 of us collectively worked 1529 different US stations! The
largest difference between the VDA and the stacks is on the Zone 3 calls.
While s50c/9a3tr/e70t worked 71/73/63 of them, I only logged 35 (but(!)
there were 132 different Zone 3 calls in our logs).
I need to state, that none of us was stressed not for a minute with a
pile-up (max. rate was around 130 Q/h and just for one hour). There was
plenty of time to work stations and the band was wide open (when it was).
Maybe one more detail, while s53rm had many signals with strong QSB (fast
and deep fading), all the signals on the VDA were very stable.
So few questions popped up:
- is 10dB signal strength (on TX and RX!) really worth only about 10% on
the QSO count?
- if I would operate VDA style from a "high callsign gain" DXCC (being red
on the everyones bandmap), would I log 1500 QSOs?
- 10dB gain does show a difference for the west coast stations, but almost
no difference to Zone 4 and 5 - how come?
- is operating style of "calling CQ, no S&P" with a zero "callsign gain"
worth 10dB of antenna gain (i.e. callsign gain = -10dB)?
- would better conditions result in higher QSO difference?
- would self-spotting be of any help (none of us used it - each of us was
spotted only 18-22 times)
I would like to hear your thoughts.
Robi/s53ww
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