[CQ-Contest] 5-over-5-over-VDA

Wed Feb 26 17:00:14 EST 2025

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 at 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 at 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
>>
>>
>>
>> --Using Opera's mail client: http://www.opera.com/mail/
>> _______________________________________________
>> CQ-Contest mailing list
>> CQ-Contest at contesting.com
>> http://lists.contesting.com/mailman/listinfo/cq-contest

-- 
Using Opera's mail client: http://www.opera.com/mail/