[TowerTalk] Takeoff angle
Bob Shohet, KQ2M
kq2m at kq2m.com
Sun Jul 23 20:59:36 EDT 2017
The lower the better? Rare when higher is better? Seriously?
Just for an example, I operated WPXSSB and WPXCW full-time (36 hours) with my 5/5/5 on 20, 5/5/5/5 on 15 and 5/5/5/5 on 10. At no time was my lowest 20 meter 5L Hygain @ 58’ even close to being the best antenna for EU. Even the middle 5L @ 82’ was down almost the entire time both weekends to the 5L @ 130’. Yes, geomagnetic cndx were extremely disturbed, but we had some sunspots. In 18 months they will be flatline and high angle high band signals from EU will be almost non-existent for the vast majority of the bottom of the cycle. As it has been for at least the past 4 sunspot cycles that I have operated in.
15 and 10 will be even worse.
My qth is in Western Connecticut about 10 miles from the W2 border so EU should be even more high angle from here than for you in W9 or for Jeff in W0.
There will be occasional times when a DX station might be briefly louder on a lower antenna than a higher one, but for the next 4 years that will be the exception rather than the rule and my stacks on 10, 15 and 20 provide a great testing ground for the signal arrival angles. This is even true for South America which is the closest continent and one might think should have stronger signal strengths with lower antennas. They don’t, at least from the East Coast. Higher is still better.
As we progress into the new sunspot cycle and the spots return, lower antennas will perform progressively better and near the peak of the cycle, you can watch the the arrival angles of signals change rapidly – the top opens the band, then shortly after it opens, the middle or second antenna down becomes loudest then the lower one and then the lowest. This happens on all the high bands 10 – 20. But now we are the opposite end of the cycle – where you want your antennas to be higher rather than lower. Signal arrival angles change throughout the opening, but the highest antennas predominate now and will continue to do so for the next few years.
As valuable as books and computer plots can be, there is nothing like actively operating contests to see how the propagation and arrival angles change throughout the contest on each of the bands with stations from every part of the globe. And being able to switch phasing combinations instantaneously provides useful real-time data as to which antennas are actually (not theoretically) “hearing best” at any time. Hearing is believing!
Sent: Sunday, July 23, 2017 7:33 PM
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Takeoff angle
If you are using the HFTA from the ARRL AB then you have all that info there
already! It’s the Elevation File. They have one for every state for EU, AFR,
AS etc etc ...
for the most part the lower the better... there are times, rare, when higher
is actually better. For example I can select top/bottom/BIP/BOP with 2
stacked 20 meter yagis using a RemoteQTH match ... the TOP is never the best
(for all practical purposes) so the choices are BIP, BOT, BOP in that order
... and indeed there are times, like in the afternoon going from here to
Africa where the BOP position can be as much as 10 db stronger than the BIP.
The differences are 8° and 19° for my terrain and location.
Be sure to put YOUR local terrain profile in. Either manually (not as bad as
some make it out to be) or using Stu, K6TU's site... unless its flat there
might well be some differences ... I literally used HFTA as one of the top
criteria (for me it was THE top) in selecting where we moved to when moving
back to SC! On some paths there can be 10's of db enhancement (or
From: Dave Clemons
Sent: Sunday, July 23, 2017 2:35 PM
To: 'Jeff Draughn'
Cc: towertalk at contesting.com ; Dave at egh.com
Subject: Re: [TowerTalk] Takeoff angle
A number of years ago Dean Straw gave some presentations on takeoff angles.
His presentation included a big binder of information (I think called "All
the Right Angles"). I don't remember who published it, perhaps K8CC or
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jeff
Sent: Sunday, July 23, 2017 12:39 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Takeoff angle
I've been playing around with HFTA trying to figure out the best height/
configuration for my antennas and it dawned on me I wasn't sure what the
best take off angles are. I know low is better than high for DX, I'm
assuming it's a range that I'm looking for.
When looking at the plots what would be considered good take off angles for
DX contests from the midwest.
What is considered too high of an angle for DX?
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