Hi Dave,
thanks for the link to Doug's presentation. At least for the ARRL DX, SOSB
category, EU location, the 6%/dB does not hold true :)
Yes, there are ways to measure the signal difference - the question was
how that difference plays in the contest with a hypothesis that high gain
at very low angles that VDA offers would compensate for the negative dB
difference at higher angles. This hypothesis was dis-proven as far as I am
concerned - if(?) west coast comes at low angles, then it needs also a lot
of gain.
Robi/s53ww
On Wed, 26 Feb 2025 05:55:04 +0100, K3ZJ David Siddall
<davek3zj@gmail.com> wrote:
Robbi,
Robi,
Very interesting indeed.
Another way to determine signal differences between two or more antennas
is to calibrate two WSPR transmitters -- 100 or 200 mW is plenty of
power >-- and use one with each test antenna configuration. Point your
beam(s) in the same direction as favored by the VDA. Adjust for coax
cable loss if >applicable (or measure at antenna) so that equal power is
delivered to each test antenna. Start the two WSPR transmitters at the
same time to get them >as correlated as possible. PSKReporter will
report reception locations and received signal strengths.
After 24 or 48 hours you should have good comparative test results for
current solar conditions. This method removes operator capabilities
from the >equation and is more granular than other methods. It also is
super easy to implement, and if one antenna remains unchanged it can be
used as a >reference antenna to measure improvements to the other
antenna (or use a third antenna for this purpose).
Insofar as QSO count / score difference per dB, I defer to K1DG, who has
suggested that each additional dB may be worth about a six percent score
>increase, see: https://tinyurl.com/8rctjr9h.
Please do let us know of any further testing along these lines.
73, Dave K3ZJ
On Tue, Feb 25, 2025 at 8:26 PM s53ww <s53ww@hamradio.si> wrote:
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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