Arriving signal polarity is indeed something that others have found to
be quite variable at times. It is generally accepted that HF skywave
signals arrive with an elliptical polarization, but the shape of the
ellipse can change pretty dramatically. And 20 to 30 db impact is not
unusual at all. Lots of Field Day stations will orient adjacent
antennas with different polarization to minimize cross-band overload.
I've thought about feeding the signals from two cross polarized antennas
to the two phase locked receivers of my K3 to investigate the real time
effects ... maybe some day I'll get around to it. What I really need to
do is learn how to program (probably with something like Python) so that
I can record the audio to a wave file and then analyze the result
properly. Maybe I'll live long enough to do that ... maybe not.
73,
Dave AB7E
On 6/27/2012 5:48 AM, Joe wrote:
> I agree, Changing the length should have little to no change of the main
> lobe angle above the horizon.
>
> But what did make a HUGE change, was what I had in the 80's I had small
> Mosley TA-33 Vintage 70's up on a Rohn HDBX self supporting 54 foot
> tower. I had the typical rotor on it of course, but I also had another
> rotor on the boom of the beam.
>
> The experiment came from the HUGE success I had with curing faraday
> rotation on my 2 meter EME system by rotating the polarity. I thought
> about the same thing on HF. the polarity is surely not just horizontal
> or vertical ever. But also always changing. So I tried a rotor on the
> boom so I can rotate it in polarity.
>
> And wow did that make a difference!!!! Max signals were rarely
> horizontal or vertical. And as they always say polarity mismatch can
> change signal levels up to 20 to 30 DB!. And boy did it ever!
>
> Now I do have to admit, polarity was not the ONLY thing changing here.
> But the antennas main lobe take off angle would be changing also. Look
> at any chart that shows take off angles that take into account
> polarity. And the vertically polarizied always had a lower angle.
>
> So between the polarity and lobe shift some really impressive signal
> level changes would happen when rotating that beam along it's axis.
>
> Joe WB9SBD
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
> On 6/27/2012 12:17 AM, David Gilbert wrote:
>> I'm afraid I don't understand. The vertical pattern of a horizontally
>> polarized antenna has very little dependency upon element length, and
>> certainly not within element lengths that would provide any reasonable
>> match to the feedline. You would lose FAR more signal to mismatch and
>> reduced parasitic gain than you would ever gain from a change to the
>> vertical pattern. I'd be very interested in any EZNEC file that showed
>> differently.
>>
>> Dave AB7E
>>
>>
>>
>> On 6/26/2012 7:46 PM, Rick Kiessig wrote:
>>>>> For actual real time optimization, you are pretty much stuck with either
>>> using stacked antennas to eliminate notches or somehow being able to quickly
>>> raise/lower your antenna as conditions require.
>>>
>>> Or perhaps using an antenna with tunable element lengths (SteppIR/UltraBeam)
>>> and changing them to optimize the antenna pattern based on the location of
>>> the other end of the QSO and current conditions.
>>>
>>> For weak signal work, the experiment I had in mind was using the estimated
>>> incoming angle only as a starting point to choose from a collection of
>>> pre-computed element lengths optimized for gain or F/B by incoming angle,
>>> and tweaking up or down from there. (I'm not expecting a big effect, but
>>> modeling wih EZNEC and 4nec2 shows reasonable trade-offs are possible). It
>>> wouldn't compensate for fast QSB, but that's not the goal.
>>>
>>> If anyone else has tried something similar, I would be interested in hearing
>>> about it.
>>>
>>> 73, Rick ZL2HAM
>>>
>>>
>>> -----Original Message-----
>>> From: cq-contest-bounces@contesting.com
>>> [mailto:cq-contest-bounces@contesting.com] On Behalf Of David Gilbert
>>> Sent: Wednesday, June 27, 2012 4:54 AM
>>> To: cq-contest@contesting.com
>>> Subject: Re: [CQ-Contest] Estimating arrival angles?
>>>
>>>
>>> VOACAP does indeed predict optimum arrival angle for any particular path,
>>> but that's based upon statistical averages -->by month<-- and has no bearing
>>> at all to instantaneous conditions ... which can change DRAMATICALLY in a
>>> matter of seconds. And, of course, there are indeed multiple arrival angles
>>> at play much of the time anyway.
>>>
>>> I have an Elecraft K3 with identical receivers that can be phase locked for
>>> diversity reception. I also have a tribander and 40m yagi on the same tower
>>> spaced about 12 feet apart vertically. One night on 40m I fed the signal
>>> from the tribander into one receiver and the signal from the 40m yagi into
>>> the other receiver ... and then fed the stereo audio output into my computer
>>> sound card with a dual-channel audio oscilloscope application running. I
>>> tuned to a 40m broadcast signal so that I could get a pure carrier when the
>>> announcer was not speaking. I sync'd the oscilloscope to one signal while
>>> observing both on the screen, and while I couldn't determine the exact phase
>>> angles because I didn't know the electrical lengths to each antenna, I was
>>> able to watch the phase difference in real time (relative phase is retained
>>> in the frequency down conversion to audio). Based upon the 12 foot spacing
>>> and the amount of phase shift I was seeing on the computer screen, I
>>> calculated that the NET arrival angle was changing as much as 20 degrees
>>> within fractions of a second ... which is not unrealistic in light of other
>>> more rigorous studies that have been done by the government over the past
>>> several decades. That net arrival angle could have been due to a single
>>> signal changing in angle or the sum of multiple arrival angles individually
>>> changing in amplitude, but the net result would be the same to a listener
>>> ... perceived fast fading.
>>>
>>> HFTA, the terrain analysis program written by N6BV that comes free with the
>>> ARRL Antenna Book, uses the VOACAP arrival angle data for its optimization
>>> algorithm and that's about as good as you're going to get for planning
>>> purposes. For actual real time optimization, you are pretty much stuck with
>>> either using stacked antennas to eliminate notches or somehow being able to
>>> quickly raise/lower your antenna as conditions require.
>>>
>>> 73,
>>> Dave AB7E
>>>
>>>
>>>
>>> On 6/26/2012 3:27 AM, Jukka Klemola wrote:
>>>> Luckily the world is not that simple we really could measure the arrival
>>> angle.
>>>> There are often more than one sky wave propagation models happening
>>>> all the time if you are in ZL2.
>>>>
>>>>> From ZL2, you work a JA, a W6 or anything else that is 'close by' ..
>>>> the propagation usually happens through at least two F2 hops.
>>>>
>>>>
>>>> To estimate how the propagation works out, I have used a DOS program
>>>> Miniprop for that purpose.
>>>> W6EL that works in WinXP machines, might have the same feature.
>>>> At least you can set the minimum radiation angle also in W6EL so you
>>>> can experiment by software the phenomena you are after.
>>>>
>>>> Maybe also VOACP has some possibilities for that, but I found VOACAP
>>>> to be largely inferior comparing to even Miniprop when I was
>>>> experimenting the low angle propagation models for long-haul paths.
>>>>
>>>> I gave OH6BG a set of feedback, so VOACAP may have been corrected or
>>>> at least improved, I do not know.
>>>>
>>>>
>>>> I have been very happy experimenting by software with W6EL and Miniprop.
>>>>
>>>>
>>>> ..yes. I still have even DOS computers around so I can use the
>>>> _Good_Old_Softwares_.
>>>>
>>>>
>>>> 73,
>>>> Jukka
>>>>
>>>>
>>>> 2012/6/25 Zack Widup<w9sz.zack@gmail.com>:
>>>>> You would need at least two separate antennas and the ability to
>>>>> measure the phase angle between the signals received by the two
>>>> ...
>>>>> On 6/25/12, Rick Kiessig<kiessig@gmail.com> wrote:
>>>>>> Can anyone suggest a good way to estimate the incoming RF arrival
>>>>>> angle for a given QSO? Are there any software tools to help in that type
>>> of analysis?
>>>>>> 73, Rick ZL2HAM
>>>> _______________________________________________
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