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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