The following discussion about the use of H/V polarization for portable eme-stations took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page.
On 5-April-1999 ON7RB wrote:
Hello OM,
Thank you for taking the time to read my questions. I hope you can give me some answers
too :-)
In the last years, I used an almost exact copy of the setup of the home station for
portbale eme work : 8 times 13 el yagi array (double reflector) built after the DL6WU
design notes, az/el controlled, horizontally polarised. The only really negative
comparison for the /p antenna is the set of lines for the phasing harness, made of H100
coax cable. Planning to replace these lines with 1/2 " CellFlex, I was wondering if
this would be worth while to get a better efficiency of the time spent on the portable
sites (e.g. LX0EME) or if I should combine the effort with changing to a H/V polarisation
switchable array ...
Here are the questions :
- can I mount 4 yagis vertical and 4 horizontal ? in this case, the portable
setup is still a work of many hours ...
- what about mounting vertically polarised yagis with booms supported by vertical tubing ?
this can never give a good result in my opinion
- if I am using 4 yagis V and 4 yagis H, why not mount the lot on 4 booms ? isn't
that what most people are doing - I've used crossed yagis 20 years ago for sat ...
- when using crossed yagis, would an X style mount give a better result than a + style
type ? an X mount would not have supports in any of the polarisation's plane
- is there any advantage in spacing the V and H 1/4 lambda ? i.o.w. should I think
of circular polarisation? and then the most important one :
- would we work more stations over a single weekend with a 4H/4V than an 8H array ?
i.o.w. would the reducing of Faraday lock-out at least compensate for the 2.5 db
gain lost ? remember that we are only on that site for a single weekend - no way to
try again another day ...
Any suggestion is more than welcome. Many thanks beforehand for your time and input in
helping to prepare our next eme/p event.
On 5-April-1999 GM4JJJ wrote:
>
> Here are the questions :
>
> - can I mount 4 yagis vertical and 4 horizontal ?
Yes, but see below...
> - what about mounting vertically polarised yagis with booms supported by
vertical tubing ? this can never give a good result in my opinion
This can be done with a small penalty - see F/G8MBI, SM2CEW and 9H1PA for
example.
> - if I am using 4 yagis V and 4 yagis H, why not mount the lot on 4 booms ?
isn't that what most people are doing - I've used crossed yagis 20 years ago for
sat ...
Exactly true Roland. There is no point in having to carry and put up 8 booms
when you only need 4.
> - when using crossed yagis, would an X style mount give a better result than a +
style type ? an X mount would not have supports in any of the polarisation's plane
For a simple H/V operation the + mount is easy and has the advantage that on H you have
better rejection of any strong V QRM from nearbye FM polarised transmitters. You don't
have that with X. X has advantages, rain does not settle on the X elements as much
as the H elements. Possibly shorter phasing lines with X config. Also support wires don't
get in the way of x config.
> - is there any advantage in spacing the V and H 1/4 lambda ? i.o.w. should
I think of circular polarisation?
No and I would not consider it worthwhile for a portable setup to try circular, you just
waste 3dB of power that most people can't use.
>
> and then the most important one : - would we work more stations over a single
weekend with a 4H/4V than an 8H array ? i.o.w. would the reducing of Faraday
lock-out at least compensate for the 2.5 db gain lost ?
I think the answer has to be yes, just look at the results in the EME contests of XPOL
stations against fixed pol stations.
> remember that we are only on that site for a single weekend -
no way to try again another day ...
Exactly, so go for maximum flexibility.
Have a lool at my web page on XPOL which has links to others like Graham F/G8MBI's where
you will get some very good advice on the options available to you.
http://www.qsl.net/gm4jjj/XPOL/xpol_array.htm
has my lastest notes on the construction of my M^2 4 * 2MXP20 array.
Mirror on http://www.braeside.demon.co.uk/XPOL/xpol_array.htm
As a footnote:
I am always amazed how portable EME stations ever get setup in such a short time. It would
take me about a month to get my station setup! Congratulations are in order to folks like
Mike K6MYC who can hand carry an EME station in an aircraft!
I was also amazed to see in DUBUS that a Russian station in the high Arctic managed to
make a working EME station from scrap TV antennas - outstanding effort that puts many of
us to shame.
On 5-April-1999 SM7UFW wrote:
I have chosen to go for the x-configuration. David GM4JJJ has
mentioned the most obvious reasons; rain, guy wires etc and I totally agree. (BTW congrats
to your new antenna, David!)
In my antenna, I have used two electrically equally long feeders for TX for two reasons;
- I can have all polarity switching relays etc inside the shack
- Each relay/feeder only needs to handle half of the power (or twice the size of the PA!)
The same applies for RX, where I can combine the two signals to any polarisation wanted;
arbitrary linear or circular for satellite. The SM5BSZ home page (http://ham.te.hik.se/~sm5bsz/) is the obvious
reference for this kind of projects. Have a look at my system at http://ham.te.hik.se/~sm7ufw/EME.html.
Maybe this isn't such a good idea for portable operation, who knows?
On 5-April-1999 K0GU wrote:
> > i.o.w. would the reducing of Faraday
lock-out at least compensate for the 2.5 db gain lost ?
>
> I think the answer has to be yes, just look at the results in the EME contests of
XPOL stations against fixed pol stations.
I would love to hear some discussion on this point. I wouldthink the number of stations
you generally can work on randoms during a contest weekend would be more with the extra
gain. However when locked during a sked maybe the polarity is worth more??
On 5-April-1999 WA6PY wrote:
My past experience as SM0PYP on 432 was that 75% of QSO's were
made with "wrong" polarization. In many cases polarization shift was not
reciprocal. For instance I was forced to transmit on vertical to be heard, but I was
receiving on horizontal.
Even for the stations very close to my QTH like 700 miles away. Some times strong
polarization dispersion was also observed, causing conversion of linear polarization to
the elliptical and sometimes even almost circular.
I do not have many experience with 144. One experience was that when I moved to a new
location 1984, I just assembled one yagi and aimed to the moon just by supporting
reflector on the ground and boom on the tree. I heard SM7BAE quite strong, but I could not
get even QRZ from him. Then I rotated yagi to vertical polarization, and he came
bask after my first transmission., BUT his signal were significant weaker. The distance
between us on the ground was about 600-700 km = 400 miles.
About 10 years ago I started to introduce new information regarding polarization on 432.
It was for example 439V ( or H ). It was sometimes help to aim the polarization,
because I figure out that is very difficult what polarization is coming out at the
other" end"
Polarization is especially important for small system stations!
On 5-April-1999 GM4JJJ wrote:
Of course one thing I had not taken into account was that there are
more and more XPOL stations QRV now, so that makes it easier for fixed Pol stations to
work THEM.
On 6-April-1999 K2LME wrote:
N1BUG's excellent ZTrack program is acompanied by an interesting
utility called AN.EXE.
Among its talents are
>Analyze a EME Log (QSOs vs polarity, non-reciprocity & declination - see the
included logs, or plug yours in)
>Calculate Path Statistics (polarity to specified grid)
>Spatial Polarity/Faraday Demo (graphical depiction)
Spending a little time playing with AN could make you wonder how you ever work anything!
ZTrack's at http://www.qsl.net/n1bug/
On 6-April-1999 G3SEK wrote:
>My past experience as SM0PYP on 432 was that 75% of
QSO's were made with "wrong" polarization.
I'd agree with Paul. In the large majority of QSOs on 432, fixed polarization is more than
3dB below optimum in at least one direction.KL7WE's statistics were almost exactly the
same as Paul's and mine: he counted 78% of QSOs that would have had >3dB degradation
with fixed horizontal. That makes a huge difference to the completion and CWNR rates.
>In many cases polarization shift was not reciprocal. For instance I was forced to
transmit on vertical to be heard, but I was receiving on horizontal. Even for the stations
very close to my QTH like 700 miles away.
Non-reciprocal polarization caused by the interaction between spatial polarization (due to
the difference in location on the earth's surface) and Faraday rotation. N1BUG and KL7WE
tied up all the theory many years ago, and KL7WE's practical operating methods for
aligning polarization work reliably and well (CSVHF Proceedings 1988).
Again quoting KL7WE, in his first 6+ years on 432 with fixed polarization he made 217 EME
QSOs. With rotatable polarization and the same antenna gain, he made 265 more QSOs in 10
MONTHS!
>Some times strong polarization dispersion was also observed, causing conversion of
linear polarization to the elliptical and sometimes even almost circular.
This is quite frequently true on 432.
>Polarization is especially important for small system stations!
Having tried it, I strongly agree!
On 6-April-1999 OZ1HNE wrote:
I think the polarity problem is much bigger on 432 MHz than on 144
MHz.An exampel: In the REF DUBUS EME contest (on 144 MHz) I worked 70 QSO's and
"only" 17 of them was worked with "wrong polarity" (not
horisontal/horisontal).
On 6-April-1999 SM5BSZ wrote:
> - would we work more stations over a single weekend with a
4H/4V than an 8H array ? i.o.w. would the reducing of Faraday lock-out at least
compensate for the 2.5 db gain lost ? remember that we are only on that site for a
single weekend - no way to try again another day ...
With everything else "normal" (1kW, low Rx noise, good operator) a 4H/4V station
should work all the stations one can expect to be qrv.
My guess is that there will be no stations trying to work an expedition like this that
will not have the capacity to work a 4 yagi station when polarisation misalignment is
excluded by polarisation diversity. Consequently the 2.5dB improved S/N that may result
from 8H will just make qso's slightly faster in the unlikely event that alignment is
perfect in both directions.
With one polarisation only the probability for a 6dB or worse loss is about 30% this means
that the chance that none of the stations has less than 6 dB polarisation loss is only 50%
when both are without polarity switching. There is a high probability for loosing a lot of
time because the signal is very weak one way or the other.
The above is based on the experience that very few active EME'ers use less than 25kW ERP
on 144MHz - and those who do are probably not active enough to try to work a single
weekend expedition.
If smaller systems are compared, the outcome is different. A cross yagi that is too small
to allow qso-ing with typical 4 yagi stations will most probably give fewer contacts than
a twice as big system without polarisation diversity!! At what antenna size 2.5dB more
gain is more important than polarisation diversity depends on Tx power and Rx
sophistication.
On 6-April-1999 WA6PY wrote:
Additional factor in my case and KL7WE, is that we were located at LAT
60deg. The ionization is much higher compare to the location towards equator. Few times I
could also observe aurorra like sound on strong signals from DL9KR, K1FO, SM4IVE and
others. This makes polarization "distortions" even more random and non
reciprocal. This was not only spatial polarization influence, but very often pure
propagation propierties. For example I worked K0RZ on vertical polarization on RX
and TX, one hour later I worked him again, and this time I was forced to TX still
vertical, but I received him purely horizontal. About two hour later I could not get his
attention calling him on vertical, but I went through on horizontal right away, and I
received him horizontaly. Spatial geometry indicated about 90 deg shift for all three
cases.
On 6-April-1999 G3SEK wrote:
OZ1HNE Jorgen Kristiansen wrote:
>I think the polarity problem is much bigger on 432 MHz then on 144 MHz.An exampel: In
the REF DUBUS EME contest (on 144 MHz) I worked 70 QSO's and "only" 17 of them
was worked with "wrong polarity" (not horisontal/horisontal).
>>
>>Paul Chominsky wrote:
>>>My past experience as SM0PYP on 432 was that 75% of QSO's were made with
"wrong" polarization.
Well, it's different on 144 and 432. Who can comment, who has experience with polarization
switching on both bands... Peter 'CEW?
On 6-April-1999 WA6PY wrote:
Also VE7BQH has experience with polarization on 144.
On 8-April-1999 SM2CEW wrote:
The "polarity problem" is not bigger on 432 in the sence
that it is more complicated mathematically, it is just the fact that Faraday rotation is
so much slower on 432.
Faraday rotation can be fixed for 6 hours or more where on 144 there is always some
rotation although one might consider it as slow. I remember that the old 1 hour long
sked's used to be called "two Faraday's" meaning that in one hour signals came
and went two times for both stations, enough to make a good contact. (Oh, I loved those
skeds, at minute -58 you heard RRR... !)
What is also different with 144 is that the signal levels are generally weaker, mostly due
to the fact that man made noise is more frequent on the lower bands but also because
polarization is always changing so it is never aligned for more than a few minutes.
It is my opinion that a 4 yagi xpol station on a short term basis would work many more
stations than a fixed pol 8 yagi station would. I have been listening to so many
expeditions over the years that were using fixed polarization, often they had huge pileups
but heard nothing. The reason was that the calling stations were in a crosspol situation.
These expeditions could complete 3-4 contacts during a moon session but 30-40 stations had
been calling, stations that normally would have made the contact quite easily had the
polarization been aligned.
So, 144 is more forgiving due to the fact that polarization does spin around but
there are times when there is not time to wait for the spin, like when working
moonrise/moonset stations.
A good 4 yagi setup will make it possible to work most stations that are on 144 EME today,
so I feel the gain is not an issue if transmit power is reasonable.
The most frustrating thing for an expedition must be to get reports "Heard you 519,
called you for 4 hours solid.... " Who want's to hear that .. ?? Better be
"Thanks for the RO/RO contact in 6 minutes ! "
There is one thing though about the polarization issue that I must point out, don't over
do it, H/V will do the job very well ! Having the option to go to any polarization
position will easily put you in a "chasing tail" situation. One needs to be very
sure of Faraday rotation and spatial offset to put the transmit polarization in the right
position. Granted, if done right it will produce maximum signals at both ends, but one
needs experience to do it right !
Graham, F/G8MBI put a small 4 yagi xpol system up for 432 a while back and he heard more
stations the first activity weekend he was on than many of the 8/16 yagi boys did purely
because he could switch polarization. He sat and listened to sked after sked between 4/8
yagi stations or bigger that were perfect copy with him but could not hear each other
because they were crosspol at the time. Pretty convincing to me that his setup would be a
winner for a one weekend expedition !
On 9-April-1999 OE5JFL wrote:
I use polarity switching (H/V) since 11 years on both 144
and 432 MHz. Although I never made statistics, I found out several things for practical
use.
On 70cm polarity is changing rather slowly, so it happened that I got 90deg offset
echos for several hours (especially during daylight). So a station with only horizontal
antennas can run into low a success rate having several skeds in such a period.
Signals from stations within Europe show almost always the same shift in polarity as my
own echos. Stations from VK/ZL I received more often hor. better than ver., from JA I
receive stations very often better vertical. Best success on transmit I have with the same
polarity as receive. Situation with U.S. stations is different because of the geometrical
path changing quite a lot. Very often I had to transmit 90deg offset from best receive to
get attention. Anyway, over the years I got a good feeling about
what polarity to choose, together with some theoretical considerations (KL7WE...)
On 2m the situation is sometimes similar to 70cm, but most time polarity is changing
much faster. So it can happen, that within a QSO lasting 10 minutes only the polarity is
changing from hor. to vert. Also I often experienced when my own echos came back best hor.
when transmitting hor., that stations less than 1000km away came in vertical. (stations I
know having only hor. pol Yagis).
So prediction is less easy on 2m, but at least with some patience you can wait for the
polarity to come around and let you make your QSO. Sometimes I switched every 10 seconds
H/VH/V... in a transmission when I was not sure what polarity would be best.
Anyway, I really like the possibility to switch polarity very much and would suggest to
everybody planning something new to add this feature, and rather pay with 1..2dB less gain
when mechanical problems are coming up.
On 9-April-1999 DK5YA wrote:
> It is my opinion that a 4 yagi xpol station on a short term
basis would work many more stations than a fixed pol 8 yagi station would. I have been
listening to so many expeditions over the years that were using fixed polarization, often
they had huge pileups but heard nothing. The reason was that the calling stations were in
a crosspol situation. These expeditions could complete 3-4 contacts during a moon session
but 30-40 stations had been calling, stations that normally would have made the contact
quite easily had the polarization been aligned.
Yepp, this is something I still remember pretty well when thinking about our last years
SV9-Expedition. We really had that huge pile-up for days and few guys were calling us deaf
and things and the clusters and this reflector were full of "nice" comments.
There was "one-way" for days plus super QRN from that nearby power plant...even
X-pol aint help in that case...
Guess next time I will take X-pols with me and a nice pump gun just to "repair"
isolators on power lines ;-)).
> The most frustrating thing for an expedition must be to get reports "Heard
> you 519, called you for 4 hours solid.... " Who want's to hear that .. ??
Not me anymore...
On 9-April-1999 Graham wrote:
Roland.....and others..some thoughts compiled over the last three
days...some or all been said before in the past...but it might spark/inspire a few....
I wandered a bit here and there but it all does relate to the expedition/xpol theme..I
also tried to answer the original questions as directly as possible...
>Here are the questions :
>
>- can I mount 4 yagis vertical and 4 horizontal ?
......yes.....but why...?....just add v elements to what you have...or maybe even part of
it....
> in this case, the portable setup is still a work of many hours ...
............yes.....4 longer crossed may be more effective....and quicker...and less
lossy..and less critical to set up.....and less weight....
>- what about mounting vertically polarised yagis with booms supported by vertical
tubing ?
................gain loss varies from near nothing...to a couple of DB in gain terms, when
implimented properly... but watch G/T....ie pattern
> this can never give a good result in my opinion
....no......wrong opinion, several of us should have made the point by now.....
>- if I am using 4 yagis V and 4 yagis H, why not mount the lot on 4 booms ?
.........indeed....
> isn't that what most people are doing - I've used crossed yagis 20 years
ago for sat ...
...........yes....you need the 'ticket to the ball game' first...which really implies 4
times 5 lambda..or what you have..for reliable qso's in a short time with say two yagis at
the other end ..
>- when using crossed yagis, would an X style mount give a better result than a +
style type ?
............maybe....this is complex...
> an X mount would not have supports in any of the polarisation's plane
.............well not completely, but the pole degredation can be reduced.....but to
generate H for other activities is NOT as easy as it looks..(especially on rx)..nor is
mounting square booms...on balance + is just as effective in a simple system and much
easier both mechanically and electrically...
>- is there any advantage in spacing the V and H 1/4 lambda ?
.........no....but some offset due to mechanical constraints is always necessary....
> i.o.w. should I think of circular polarisation?
>
.....forget it.....
>and then the most important one :
>- would we work more stations over a single weekend with a 4H/4V than an 8H array ?
........probably....but better 4 bigger ones...or do V elements for 4 of what you have and
run all 8 H with 4 giving V, or do the lot..??...needs more thought..
> i.o.w. would the reducing of Faraday lock-out at least compensate for
the 2.5 db gain lost ?
..........in general terms NO.(with caveats see later)..but in time restricted terms YES..
> remember that we are only on that site for a single weekend - no way
to try again another day ...
>
...........exactly.....
>Any suggestion is more than welcome. Many thanks beforehand for your time and
input in helping to prepare our next eme/p event.
>
and..gm4jjj...
>For a simple H/V operation the + mount is easy and has the advantage that on H you
have better rejection of any strong V QRM from nearbye FM polarised transmitters. You
don't have that with X. X has advantages, rain does not settle on the X elements as much
as the H elements. Possibly shorter phasing lines with X config. Also support wires don't
get in the way of x config.
first part absolutely a VERY good point even out here in the sticks where in general it
can be pretty quiet it helps with all sorts of odd noises...second part ...if you have to
worry about rain your yagi is TOO gain optimised/match compromised and unless in a very
stable and well known 'home' configuration forget it.....even then...
and..sm7sjr...
>I have chosen to go for the x-configuration. David GM4JJJ has mentioned the most
obvious reasons; rain, guy wires etc and I totally agree. (BTW congrats to your new
antenna, David!)
>
maybe obvious reasons but this clearly doesn't work because everytime it rains/snows you
are on here moaning about it......I am not unsympathetic, but it does show that it doesn't
work, so no point to claim it does.....it can help upto a point, but once you step over
the line in match compromising you've had it...
and ..Jay....
>I wouldthink the number of stations you generally can work on randoms during a
contest weekend would be more with the extra gain.
no.....absolutely not......
as an aside I don't like the word * locked * because it's not the case on 144, faraday
moves more readily it seems than on 432, but of course as faraday moves the relative TX/RX
positions with respect to each other do not, necessarily, in all cases..and some paths get
better, some get worse.so you can still be snookered....
bottom line is a random weekend on polarity capability versus a random weekend on fixed
polarity, for a given gain, is no contest...and especially from your U.S. location, you
have a BIG activity disadvantage at favourable fixed polarity reciprocity.
.as for versus MORE gain..
course in an ideal world you need both Gain and polarity diversity...
this is NOT as simple as it looks and polarity is not necessarily the 'optimum'
system...it depends on the threshold of 'workability' achieved from a system in the first
place, the higher up the gain table you climb the less benefit comes from polarity, but in
a flat out race in either time restricted or contest situations then simple polarity
switching is probably worth more in efficiency terms than 3db (ie MORE than doubling a
fixed polarity array) and a more truly diverse polarity system (with at least the 45
degree angles available) will likely compete very well with even a three times bigger
array...
leifs point about 'majority capability' at the other end is what makes most of this
true....and , ESPECIALLY from the U.S. available station distribution in spatial terms..
In any event, Polarity should NOT be implimented at a cost of compromising optimum gain in
at least one fixed plane....it should be viewed as a "benefit over", not a
"substitute for"..for longer term benefit..
but for most folks it is much easier to get polarity than 3db more...and the 3db more will
not fix the issue for a high percentage of the time...or even at all on certain paths...
....and..Dave k2lme...
>N1BUG's excellent ZTrack program is acompanied by an interesting utility called
AN.EXE.
>
>Among its talents are
>
>>Analyze a EME Log (QSOs vs polarity, non-reciprocity & declination - see the
included logs, or plug yours in)
>>Calculate Path Statistics (polarity to specified grid)
>>Spatial Polarity/Faraday Demo (graphical depiction)
>
>
>Spending a little time playing with AN could make you wonder how you ever work
anything!
true it's a VERY good explanation and software in general....HOWEVER I personally treat
with some caution...it makes a somewhat rash assumption, in my opinion, that a) polarity
remains clearly defined at all times and b) faraday is truly reciprocal.....I have my
doubts on both counts...if in doubt try anyway...the dismissal of low dec times (often
with other parameters good) has/will not benefit activity....this is very good work that
has unfortunately not been clearly understood, or, wrongly interpreted, by many....
use as a 'guide' and for the excellent explanation of the geometry..NOT as 'a tablet of
stone'....
...and ian g3sek....
>Well, it's different on 144 and 432. Who can comment, who has experience with
polarization switching on both bands... Peter 'CEW?
It appears to be different here thats for sure....I can only say 'appears' with simple
switching....because I need time and some assumptions to draw conclusions..I get no
instant results here...
my comparisons with Peter CEW via 20m in real time while we both listen on 144 have
shown a high proportion of anomolies between us, with only small spatial differences
between us, when both listening to the same target station, we have repeatedly seen (heard
to be more precise) quite different optimum rx polarities at our respective QTH's....and
made echoe tests and qso's with polarity all crossed up between us.....
I should probably get off my backside and add another 3db gain here and full polarity
diversity so I could compare meaningfully with leif....but my interest in these things is
'passing' interest...my main interest is just doing it....and I have been having fun with
the QRP stuff....
432 I have not comparison tested, but it is quite clear the periods of polarity stability
are longer, more stable and can extend for hours or even a whole day....also I see no
'jumps' that are very common on 144....one period H, next equal, next solid V, all in
three minutes....sometimes even less...
My very small 432 array shows clearly why folks with 4 or even 8 yagis at each end waste
so much time and also why scheds at 432 are frequently even more of a waste of time than
at 144...why they have become the majority modus operandi of choice beats me....:-0
The premise that "scheds are needed and work, because there are few on random"
is a self fulfilling prophecy.....(on BOTH bands)..
....and...Paul..sm0pyp
>Additional factor in my case and KL7WE, is that we were located at LAT 60deg.
>The ionization is much higher compare to the location towards equator. Few times I
could also observe aurorra like sound on strong signals from DL9KR, K1FO, SM4IVE and
others. This makes polarization "distortions" even more random and non
reciprocal.
absolutely....I believe from my observations of both differences on say kb8rq and w5un
where Gary is generally much more clearly defined and Dave appears very often to be less
well defined, and comparing with Leif's reports from time to time and the real time
comparisons with peter CEW that things are VERY different in the north versus south
area.....
...and leif..sm5bsz...
>With everything else "normal" (1kW, low Rx noise, good operator) a 4H/4V
station should work all the stations one can expect to be qrv.
>
this is a good point also..with which I agree....but rolands 4 will be somewhat less than
the more common 10m booms, so he could be a db or so short of an 'average' station in my
opinion..??...
>If smaller systems are compared, the outcome is different. A cross yagi that is
too small to allow qso-ing with typical 4 yagi stations will most probably give fewer
contacts than a twice as big system without polarisation diversity!! At what antenna size
2.5dB more gain is more important than polarisation diversity depends on Tx power and Rx
sophistication.
>
and time available to try....again I generally agree, my opinion on size, to try to get a
few more started on 144 eme with anything perhaps ? :-
I would say 1kw (a real one at the yagi) and 14 to 15 dbd is around the limit for a
reliable'ish single yagi link with 4 yagi stations..and would add that both the rx and the
operator have to be working well at both ends...and WITHOUT polarity (at one end or the
other) it might take several goes ..BUT, some of the near constant 'mid' spatial
point to point links might NEVER happen without polarity capability, so there would be a
significant bias in a small stations log towards either same continent QSO's (more time to
utilise the times of good match and good apparent recipricosity) and say for example from
most of europe to west coast US...(90 or at least very high spatial quite common)
this is based on hearing about 40 stations on one here with no elevation and only
moonset/rise windows available and fixed H polarity, in about three onths....and
observation of consistant strengths with my current 16.x dbd, where frequently 4 yagi guys
are still workable with several dB of attenuation in line...
In europe I think 100 initial stations with say a single M2 17 should be possible....but,
without pol capability it might take a long time and it would be much harder to do at all
from many stateside locations.....but you should still try...
...and hannes ..oe5jfl...
> Also I often experienced when my own echos came back best hor. when transmitting
hor., that stations less than 1000km away came in vertical. (stations I know having only
hor. pol Yagis).
Also seen this, there are also certain stations that seem quite consistantly anomolous in
polarity as well on 144...best and most consistant example is I2FAK.....the majority of
other I's and southern Europe (the ea boys) will be firmly Horizontal with no trace
vertical and at around 500 to 600 km away my echoes with be H up and H back, and Franco
will be dominantly vertical.!!!.even allowing for the higher erp from Franco's set up and
times when I can hear him both V and H, does not explain this....
....and peter sm2cew....
>The reason was that the calling stations were in a crosspol situation. These
expeditions could complete 3-4 contacts during a moon session but 30-40 stations had been
calling, stations that normally would have made the contact quite easily had the
polarization been aligned.
this is true...BUT.....
also made much worse by endless and pointless scheds....
The guys that go on expedition and run sched freq and random freq simultaneously and DO
pay attention to the random freq when unable to hear the sked partner do process
quicker....
with fixed polarity you need more time spent on random to 'find' the good times and good
polarity matches...
endless scheds mean you are tied up trying hopeless paths when good paths to elsewhere are
optimum..... a double whammy... because not only does it doyou no good, but prohibits
those that might do some good....so even in a limited hobby time situation scheds are not
the answer.....but x pol is...
perhaps the one valid efficiency/fairness rational for scheds would be based on common
moon time though....
polarity could also help in pile up situations at the expedition end, a quick flick of the
switch should make picking one out much easier....
....and...Finally.....
to try to quantify statistically the benefit of having either complex or simple polarity
diversity is VERY tricky....simple statements about xx% of the time it is better than
purely having more gain are a bit dodgy because they assume uniform distribution of
stations to be worked, and uniform movement of faraday and uniform common moon between
locations ...the second is probably true over a LONG averaging period, but the first is
never true, nor the third....so analysis of logs, as well as application of pure 'theory',
even if correct, is not always to be trusted....
Europeans maybe see an apparent less than real benefit (in theoretical terms) in logs
because of the 70:30 or even 75:25 ??..bias of european activity to US activity..(on
144)...and the wake/sleep patterns and moon availability time between tricky spatial
locations....
this is perhaps another reason for the apparent bigger benefit observed on 432 where the
ratio of activity (or at least active cq'ers) is a little different ???
Roland, do it...........
On 10-April-1999 G3SEK wrote:
Thanks, Graham, for such a long and thoughtful posting (and for the
time it took to put everyone else's messages together).
Just one point I'd like to comment on, from the viewpoint of continuously rotatable
polarization which gives more detailed
information than switched H/V (I'll come back to that later):
>>Spending a little time playing with AN could make you wonder how you ever work
anything!
>
>true it's a VERY good explanation and software in general....HOWEVER I personally
treat with some caution...it makes a somewhat rash assumption, in my opinion, that a)
polarity remains clearly defined at all times and b) faraday is truly reciprocal.....I
have my doubts on both counts...if in doubt try anyway...
a) On 432, polarity doesn't remain clearly defined at all times, but there is always
enough difference between the best and worst polarizations to make rotation/switching
capability useful to have.
b) Faraday may not be truly reciprocal - without co-operative tests between two stations,
it's impossible to tell. With continuous rotation, you can find THE BEST polarization for
receive, and KL7WE's method almost always gives you A GOOD polarization for transmit...
good enough for the other guy to hear you, if he's got his ears on. KL7WE's method - which
assumes that Faraday IS reciprocal - is usually good enough to get a QSO in the log, so
that's near enough for me!
Coming back to H/V switching, and time-limited operation such as Roland's DXpeditions, I'd
say go for it! When Faraday is varying quickly (as on 144) it will increase your QSO rate,
and when Faraday is stuck at 90deg it will always get your station out of that hole.
As regards the size of antennas, I agree with Graham. Do not make the antennas any smaller
because you are using H/V, but add vertical polarization to antennas of the existing size.
On 10-April-1999 ON7RB wrote:
Hello OM,
Oh boy, did I start all this?
First of all, many thanks to all who gave their comments and answers to my questions and
also to the OM who gave interesting background information on the polaity issue.
Special thanks to Lionel and Graham for a nice roundup on the matter: it is clear to me
now that I should not reduce the antenna gain (abt 21 dBd) and stick to the 8 x 6 m boom
yagi's but mount either 8 or at least vertical yagis as well.
Keeping in mind that a portable station is aiming at making a maximum number of initials
in a short period of time, preferably with OM who did not work the DXCC, QTH square of
special prefix before, we have to go for a simple system that can be set up in less than a
day. We are indeed losing a lot of valuable time in skeds that are nil or nc because of
polarity problems with no much better results in random at that moment either (oh yes, did
I call Udo for hours myself too in SV9 ...) and for a 40 hour period this is no good (I
almost wrote NFG).
If you have detailed pictures of the actual mounting of H/V on a single boom, let me know
your URL. I will not try to invent the wheel.
BTW next year, 2000, our city is celebrating the 500th birthday of emperor Charles V (in
Dutch: Keize Karel - born at 1/2 mile from my place of birth, but his expeditions were a
bit different from ours). The yearly convention of the UBA (Union of Belgian Amateurs)
will be held at St Peter's Abbey at the highest point in Ghent (11 m asl) and we will
mount the portable eme system in the square. There will be a specail event call (of course
we will try OT500KK), so watch out for more news about this event.
(Note: I'm not showing any E-Mail
address here in order to avoid them from being collected by SpamBots. You can
possibly find the E-Mail addresses of the above OM at QRZ.COM.)
This discussion is still not closed. If you have any opinions or additional
related information you would like to be published here, just send
me an E-Mail
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