[CQ-Contest] Is better antenna isolation also diminishing antenna azimutal pattern distorsion?

SM0HRP kari at sm0hrp.se
Sat Jun 4 04:32:06 EDT 2022

Hi George,
Thanks for the inputs. I was a little unclear with "150 km" to other RBN stations. I meant RBN spots readings from dx stations (USA, Japan..) of my station and nearby stations. 
I agree with what you say about things getting complicated. It is a difficult issue.
One thing I thougt, not so difficult to do, was to compare RBN sigs in EU and US when I switch between no Bandpass filters (= 25-40 dB isolation) to Bandpass filters in (= 85-95 dB isolation). Assuming stable signal conditions of course. 
Unfortunately I cannot measure antenna plot signals further away than some 100 meters. My QTH is an old island. 
A great thing to do would be to measure the vertucal antenna plot pattern with a drone like Tom N6BT did in measuring the vertical antenna pattern on sloping terrain.
Wishing you all a good weekend.
73s Kari SM0HRP

Skickat från min iPhone

> 3 juni 2022 kl. 18:52 skrev George Fremin III <geoiii at kkn.net>:
> On Fri, Jun 03, 2022 at 02:30:52PM +0200, SM0HRP Kari Gustafsson wrote:
>> Issue: Antenna isolation measures reveal that my antennas couple strongly
>> about - 30-40 dB without any filtering. But I have invested in high power
>> bandpass filters to get down the harmonics under S7 on all bands.  Comparing
>> my RBN spots with nearby "smaller antennas" close to my QTH (some 150 km
>> away) I have experienced worse antenna strength signals into many
>> directions.
> RBN data with stations 150 km (or even closer) will likley not produce
> very good data.
> At any distance from your station - and even different height antennas
> at your location can produce very differnt signal levels second to
> second.  The ionosphere changes all the time and signals generated an
> different locations or even at diffrent arrival / takeoff angles will
> vary in signal level a great deal over time.
> You would need to run these tests for some much longer periods of time
> with a lot more data than any RBN system will give you.
> I have seen wild variations even on what I would think is a short line
> of sight path.  I have a nearby ham that is about 5 miles or so away.
> This path is line of sight.  So I thought I could compaire my two 40
> meter yagis.  During the day I tired to do this with him.  But just a
> steady carrier out of one of my antennas had fairly large QSB at his
> reciever.  I was very surprised. I am guessing that there were
> multiple modes of propagation between us that was causing this QSB.
>> How do you contesters perceive these kind of antenna isolations issues on
>> big Christmas Tree stacks? Anyone been trying to solve antenna patten
>> distortion issues like this and what are the lessons learned?
> I am sure you could try to measure all of the interactions between
> antennas but I would think that in many cases it would be hard.
> Sometimes they are obvious and I suspect that many times it would be
> very hard.  I know some station owners try to do all sorts of little
> things to get the last little bit of perfromace out of their systems
> (ie. K3LR).  It would be interesting to know if he has tried to figure
> out the things you are talking about at all or even a little bit at
> this station.
> For me - I try to do some things - like not have antennas / towers
> directly in front of other antennas for key beam headings.  The tower
> locations were thought about a long time before holes were dug.  For
> most of us - you can not solve this for all beam headings unless you
> were to put up arrays that all point away from eachother for most or
> all beam headings.
> I guess you could take it all down - including the towers and put up
> one system at a time and figure out how to do signal measurements that
> you can prove you can repeat excatly every time you do them and then
> redo them wiht each change in your station.
> I think for most if not all of us this is impractal. 
> Computer models have gotten good but I suspect that modeling an entire
> station such as mine or enen yours might be very hard to do.  The
> variables get out of hand quickly.
> As a result, I and many others make choices that are compromises. 
> For me, they are things I know could or might be better - but due to
> cost constrants or space constrants the only way I could have the
> 'perfect' is not have the 'good'.
> I recall years ago a ham posting on Tower Talk or maybe here on
> CQ-Contest something to the effect of:
> "I have a 2 element 40m yagi, but I can only get it up 50 ft.  Since I
> know that is too low to be any good on 40 meters I have not put it up
> and it is in the box in my garage. And, no it is not for sale."
> And all I could think is - that is silly.  It will work at 50 ft.
> Maybe not as well as say 150 ft but it will work much better at 50 ft
> than it will sitting in the box in the garage.
> -- 
> George Fremin III - K5TR
> geoiii at kkn.net
> http://www.kkn.net/~k5tr

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