One of my senior ham friend did help me morally a bit providing what was unknown to me then called HFTA. That analysis stated that, I will loose my sight in the direction of this building which is 320 deg to around 30 Deg north. And it happens to be prime area for contesting and DXing over the poles!.
Recently I purchased ARRL's Antenna handbook. The CD which came with it contained HFTA software written by N6BV. I got hooked to it once I learnt how to use it. It opened up new paradigm for me on HF ray propagation and study the effect of stacking, antenna height with respect to immediate terrain. In combination with K6TU.net 's excellent terrain data service. I started doing many hours analysis of locations I had been recently as well.
CQWPX CW 2018 was the first contest after the high rise got completed. This contest was to test my understanding and vola... It really did reflect what was predicted. Signals were way down than it used to be. Partially overall HF weather also had a play I am sure.
Following are the graphs of these changed conditions. My terrace is at 140 ft level and around 150 ft from me is 180 ft tall building.
I plotted the graph with antenna at popular 50ft level on flat reference ground(Green), 150Ft level without the highrise (Blue) at 330 deg and current condition with Highrise (Red). Purple bars show %ge times signal arrival based on statistics.
We can see at 150ft level, there were deep nulls with signals below reference level. But then, there was surge in gain at low angles. No wonder why I used to catch K3LR and other long haul DX before many could hear them. But see what happened to me now. Red line barely rises above reference and gain is no where near compared to peak gain of 16dbi at 7 Deg I had earlier (down by 15 dBi now i.e 2.5 SUnits or more). Less of make and lot of break moments. We can also see that between 3Deg and 13 Deg there is statistical average of 5% or more signal arriving. All these chances are lean now.
Following is similar graph for 15Mtr band.
And this reflected in my score. I used to have restricted grade earlier and best score was in 2015 CQWW CW with nearly a million points. I could achieve this with 2 element Hex and 50Watts only. End of 2017 in the same contest I could only manage 600K points, that too with 400 Watts and Spiderbeam. i.e. effectively 9dB (due to Amp) + 1.5 dBi (avg spiderbeam increase) = 10.5 dBi gain.
This gain in forward direction was negated by the high rise on transmit. On receive it is only 1.5 dBi, which will be of no use as building is blocking most of the low incoming signals. In total effect, i may be sounding similar to my restricted grade signal to DX, but if they respond and signal rays arrive at those angles, I will never hear them :(.
Lastly, 150 Feet height was not the best in both the cases either. One can see deep nulls at some elevation angles with good %ge of signal arrivals. Most of the contesters have mono bander stacks just to overcome those deep nulls. Following is stack of two number of 3 element yagis at 90 and 120 feet. See how it moves the nulls to right making space for desired angles.
Today, I feel I know many of these wonderful areas of propagation due to software such as HFTA, but handicapped to try the improvements. I am hoping that in the future, I can go to right places and put portable stations for contests!
Cheers
VU2XE Kiran
Disclaimer: As usual, this blog and its content is only based on my own personal experiments and observations. I share it for fun and in hope to kinder some curiosity. I am no expert in these areas. Sometimes, my conclusions may not be accurate. For accurate information you are suggested to look out for original sources and experts in these areas.
