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CX2SA > SATDIG 20.09.08 22:12l 891 Lines 32248 Bytes #999 (0) @ WW
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Today's Topics:
1. Re: Polarity questions (Tony Langdon)
2. Re: Polarity questions (Edward Cole)
3. Re: Polarity questions (Edward Cole)
4. Re: Polarity questions (Art McBride)
5. FS: Wiltron Scalar Network Analyzrer (Chris Hackworth)
6. Re: Polarity questions (Nate Duehr)
7. Re: Polarity questions (Tony Langdon)
8. Re: Polarity questions (francesco messineo)
9. Re: Space-X to launch flight 4 (Lee McLamb)
10. Re: Polarity questions (Anthony Monteiro)
11. Re: Polarity questions (Michael Tondee)
12. Re: Polarity questions (James Duffey)
13. Re: Polarity questions (Ernie)
----------------------------------------------------------------------
Message: 1
Date: Sat, 20 Sep 2008 15:24:53 +1000
From: Tony Langdon <vk3jed(AT)gmail.com>
Subject: [amsat-bb] Re: Polarity questions
To: n3tl(AT)bellsouth.net, Clint Bradford <clintbrad4d(AT)earthlink.net>,
amsat-bb(AT)amsat.org
Message-ID: <48d4892d.1f588c0a.36e6.ffff9e53(AT)mx.google.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 09:23 AM 9/20/2008, n3tl(AT)bellsouth.net wrote:
>I don't-at-all disagree with the concept that working AO-27, AO-51
>and SO-50 isn't terribly difficult with a handheld station. Frankly,
>that has really (and pleasantly) surprised me. However, I do believe
>that adjusting polarity when hand-holding the Arrow provides
>improved performance during many passes.
It makes a big difference in many cases.
73 de VK3JED
http://vkradio.com
------------------------------
Message: 2
Date: Fri, 19 Sep 2008 21:42:54 -0800
From: Edward Cole <kl7uw(AT)acsalaska.net>
Subject: [amsat-bb] Re: Polarity questions
To: amsat-bb(AT)amsat.org
Message-ID: <200809200542.m8K5gsd0022591(AT)malik.acsalaska.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
If I may try to interpret what Clint wrote:
If a yagi has 15 or 20 dB more gain than needed to receive a decent
signal, then one can "throw away" some of that gain to cross
polarization loss and still have enough gain to adequately receive a
signal. Sort like saying if you have a 150-foot dish for receiving
AO-51 it don't matter!
But it "does matter" about polarization as far as maximizing
signal. A yagi is not different than any other linear antenna in this
respect.
Now I will have a 22-element CP 2m yagi and 42-element CP 70cm yagi
for satellites. This is obvious overkill for working the Leo
sats. It is the old standard for mode-B sats like AO-10/13. With
this pair you had really good signals with those old satellites. If
and when we get another Heo, they will be appropriate for mode-UV,
LU, US, etc. (of course this will require 1268 and 2400 antennas for
half the link).
On the HF bands polarization is generally less important because the
ionosphere messes with polarity when the signal is
refracted. Perhaps this is where that saying originates. If so, be
cautious about generalizing and applying to VHF/UHF/and above! Get a
copy of the ARRL Handbook or Antenna Book and read it. The
information is in them. There are even better antenna texts like
Jasik and Kraus if you like calculus.
73 Ed - KL7UW
At 03:23 PM 9/19/2008, n3tl(AT)bellsouth.net wrote:
>" ... and the polarization of the Yagi makes no difference in
>quality of TX/RX signal."
>
>I know I haven't been working the satellites nearly as long as Clint
>and many others - and with all due respect, my friend - I have to
>disagree with the above statement. I routinely work passes during
>which I swing my Arrow through, and sometimes beyond, 90 degrees to
>maintain signal quality. There also have been times when a quick
>twist of the wrist has made the difference between making a contact
>and getting a new grid square ... and not.
>
>I don't-at-all disagree with the concept that working AO-27, AO-51
>and SO-50 isn't terribly difficult with a handheld station. Frankly,
>that has really (and pleasantly) surprised me. However, I do believe
>that adjusting polarity when hand-holding the Arrow provides
>improved performance during many passes.
>
>73 to all,
>
>Tim
>
>-------------- Original message from Clint Bradford
><clintbrad4d(AT)earthlink.net>: --------------
>
>
> > >>...20-dB, assuming the signal is pure circular
> > polarization...linear, then -3 dB...difference between RHCP and LHCP
> > is 20 dB...difference between Horizontal and Vertical Linear is 20
> > dB...difference between (RHCP or LHCP) and (Horizontal or Vertical) is
> > 3 dB...the VHF/UHF Manual handbook says 20 -30dB...in the real world,
> > expect around 20~25dB loss from being completely cross-
> > polarized...Between linear and circular, expect about 3dB loss...
> >
> > Ahh, thank goodness for the engineers...
> >
> > Just know that to get started working the FM satellites, you do not
> > need to spend much to make successful contacts...Working AO-51 from
> > Southern California (which some claim is not a "real world") at a Watt
> > or so with an HT and Arrow Antenna is a breeze, and the polarization
> > of the Yagi makes no difference in quality of TX/RX signal.
> >
> > And as you refine your satellite comms requirements, you can spend
> > more money!
> >
> > Clint Bradford, K6LCS
> > 909-241-7666
> > _______________________________________________
> > Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the
author.
> > Not an AMSAT-NA member? Join now to support the amateur satellite program!
> > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>_______________________________________________
>Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the author.
>Not an AMSAT-NA member? Join now to support the amateur satellite program!
>Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
------------------------------
Message: 3
Date: Fri, 19 Sep 2008 21:59:57 -0800
From: Edward Cole <kl7uw(AT)acsalaska.net>
Subject: [amsat-bb] Re: Polarity questions
To: "Michael Tondee" <mat_62(AT)netcommander.com>
Cc: amsat-bb(AT)amsat.org
Message-ID: <200809200559.m8K5xvto035317(AT)hermes.acsalaska.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Michael:
At 05:53 PM 9/19/2008, Michael Tondee wrote:
>I may have misunderstood but the way I got it when I was researching
>homebrewing yagi's for my sat station is that if you had to fix the antenna
>to either RHCP or LHCP and could not switch between the two because of cost
>or complexity or whatever other reason that your best compromise would be to
>go with linear polarization.
It might be easier to wire for just one sense of CP (maybe a little
cheaper), but the complexity is not that big a deal. You can read
how to do it in the Satellite Experimenter's Handbook by Davidoff
(available from Amsat or ARRL).
> Feed harnesses for homebrew CP antennas are a stumbling block for me as I
>don't have a grid dip meter or SWR anylyzer to properly figure coax velocity
>and electrical length. If you don't get the phasing harnesses the right
>length then you won't get CP anyway.
You are making too much of a big deal out of this. Velocity factor
is published by coax manufacturers so you do not need instruments to
get close.
1/4 WL = Vf * 492/Fmhz in feet
1/4 WL (RG-213) = 0.66 * 492/144 = 2.25 feet or 27-inches
If you are off 5% it will not destroy the circularity. Most hams get
it "close enough". Of course if you are off by a quarter wavelength
or more it will matter (20-inches at 144-MHz). I know you can get it
within an inch and it will work fine. More accuracy produces a better SWR.
If you plan to build much VHF and above stuff a SWR meter is a good
basic piece of equipment to have.
> I use two of the "cheap yagi" designs by Kent Britain in vertical
>polarization and rotate them with a homebrew "SAEBRTrack" Az/El rotor box
>and old Gemini OR-360 TV rotators. Works well enough for LEO's anyway.
>73,
>Michael, W4HIJ
Sure, linear antennas only sacrifice 3-dB of gain in
crosspolarization with a CP signal. Often squint angle make such
signals elliptical so the loss can be less.
GL
*****************************************************
73, Ed - KL7UW BP40iq, 6m - 3cm
144-EME: FT-847, mgf-1801, 4x-xp20, 185w
http://www.kl7uw.com AK VHF-Up Group
NA Rep. for DUBUS: dubususa(AT)hotmail.com
*****************************************************
------------------------------
Message: 4
Date: Fri, 19 Sep 2008 21:49:32 -0700
From: "Art McBride" <kc6uqh(AT)cox.net>
Subject: [amsat-bb] Re: Polarity questions
To: "'Angus'" <angus(AT)young5769.freeserve.co.uk>, <amsat-bb(AT)amsat.org>
Message-ID: <3AC1A65234E64E309BEE81949F0B746D(AT)kc6uqh>
Content-Type: text/plain; charset="US-ASCII"
When deciding is Circular worth it, look at your local terrain.
Reflections are the opposite polarity.
If there are large buildings or mountains that create reflections as the
satellite travels there will be a large amount of QSB from the add/subtract
of the signal and the reflections at the antenna.
Circular to circular reduces the reflections by more than 20dB, and also
reduces rotational fading from the satellite spin.
If you are out on a prairie or 20 miles out to sea you most likely will not
need circular polarization.
Art,
KC6UQH
-----Original Message-----
From: amsat-bb-bounces(AT)amsat.org [mailto:amsat-bb-bounces(AT)amsat.org] On
Behalf Of Angus
Sent: Friday, September 19, 2008 1:19 PM
To: amsat-bb(AT)amsat.org
Subject: [amsat-bb] Re: Polarity questions
By having circular polarisation that matches the satellite (RHCP or LHCP but
the same polarity) you have very little QSB fading during the pass of the
satellite. Using my own system I normally start a pass on Horizontal as the
satellite is at AOS and then when it rises switch to the correct circular
polarity and as the satellite gets near to LOS I am back on horizontal
polarity with good quality signals through the entire pass.
try listening to a NOAA weather satellite on 137mhz on a fixed polarity
antenna i.e V or H and for some of the pass the signal is very good but as
the signal changes polarity the signal drops down into the noise and through
the satellite pass you will get these peaks and troughs of signals. This is
why if possible it is best to use circular or better still have the ability
to switch polarity during the pass.
regards
Gus
----- Original Message -----
From: "pe0sat" <pe0sat(AT)vgnet.nl>
To: <amsat-bb(AT)amsat.org>
Sent: Friday, September 19, 2008 7:02 PM
Subject: [amsat-bb] Re: Polarity questions
>
>
> On Fri, September 19, 2008 16:58, Ryan Butler wrote:
>> Tim Tapio wrote:
>
> Hi Tim,
>
>>> How much signal reduction is there as the result of having the wrong
>>> circular polarization?
>
>> The difference between RHCP and LHCP is 20 dB
>>
>> The difference between Horizontal and Vertical Linear is 20 dB
>>
>> The difference between (RHCP or LHCP) and (Horizontal or Vertical) is 3
>> dB
>
> If I understand right, you only get 3db extra when using CW/CCW but I have
> also read somewhere that you also lose 3db when running CW/CCW so why use
> Circulair polarisation and not just Horizontal or Vertical pol.
>
>> Ryan, NF0T
>
> 73's Jan / PE0SAT
>
> _______________________________________________
> Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>
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Message: 5
Date: Sat, 20 Sep 2008 01:19:31 -0400
From: "Chris Hackworth" <n8phucjh(AT)gmail.com>
Subject: [amsat-bb] FS: Wiltron Scalar Network Analyzrer
To: AMSAT-BB(AT)amsat.org
Message-ID:
<298264bf0809192219g12471b51yefcf3ebbe488c738(AT)mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Functional Wiltron Scalar Network Analyzer. From My personal test
bench. Analyzer, sweeper, detector, manuals ,cables. Its all there.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MESELX:IT&item=2
20283842314
--
Chris N8PHU
ET1(SW) USN (Ret)
Chief transmitter Heavy SES-Americom
------------------------------
Message: 6
Date: Sat, 20 Sep 2008 00:56:56 -0600
From: Nate Duehr <nate(AT)natetech.com>
Subject: [amsat-bb] Re: Polarity questions
To: AMSAT BB <amsat-bb(AT)amsat.org>
Message-ID: <ABA0F2FD-0ACF-4F80-8049-261DC0B6AA9A(AT)natetech.com>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
On Sep 19, 2008, at 11:24 PM, Tony Langdon wrote:
> At 09:23 AM 9/20/2008, n3tl(AT)bellsouth.net wrote:
>
>> I don't-at-all disagree with the concept that working AO-27, AO-51
>> and SO-50 isn't terribly difficult with a handheld station. Frankly,
>> that has really (and pleasantly) surprised me. However, I do believe
>> that adjusting polarity when hand-holding the Arrow provides
>> improved performance during many passes.
>
> It makes a big difference in many cases.
I'm kinda sitting here chuckling that people have "opinions" on how
physics works. :-)
Tony's right: Of course polarity makes a difference. It's well proven
physical science at this point in our RF history.
When the physics don't match the real-world experience, look for
variables that might be affecting the test.
For example, most FM receivers aren't linear in their response from
"noisy" to "quieting" on weak-signals.
If the satellite is moving, rotating, and generally "messing up" the
test, it's hard to always see the results of polarity changes -- mix
in trying to do it by hand, and different people's tolerance for
listening through noise, different receiver sensitivities, higher and
lower gain antennas, and pretty soon -- the whole test is pretty non-
objective.
Some people may say "not switching polarity works fine" and on a
particular day, with a particular rig, antenna, satellite orientation
or motion, and a different set of between the ears DSP filters (ears)
than the next person, their perception may be accurate for their
experience -- but it doesn't change the physics... 20 dB loss is still
20 dB of loss due to a polarity mismatch.
This is just the difference between the practice of radio
communications, and the hard science of it all...
--
Nate Duehr, WY0X
nate(AT)natetech.com
------------------------------
Message: 7
Date: Sat, 20 Sep 2008 19:54:42 +1000
From: Tony Langdon <vk3jed(AT)gmail.com>
Subject: [amsat-bb] Re: Polarity questions
To: Nate Duehr <nate(AT)natetech.com>, AMSAT BB <amsat-bb(AT)amsat.org>
Message-ID: <48d4c86a.1ebc720a.08d5.ffffa110(AT)mx.google.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 04:56 PM 9/20/2008, Nate Duehr wrote:
>Tony's right: Of course polarity makes a difference. It's well proven
>physical science at this point in our RF history.
Indeed. :)
>If the satellite is moving, rotating, and generally "messing up" the
>test, it's hard to always see the results of polarity changes -- mix
>in trying to do it by hand, and different people's tolerance for
>listening through noise, different receiver sensitivities, higher and
>lower gain antennas, and pretty soon -- the whole test is pretty non-
>objective.
Well, I had a pretty good way of determining polarisation. I used to
hand rotate the antenna through 180+ degrees, and there WAS a
definite peak and null, as you'd expect. This required frequent
adjustments, as the polarisation would shift significantly during a pass.
>Some people may say "not switching polarity works fine" and on a
>particular day, with a particular rig, antenna, satellite orientation
>or motion, and a different set of between the ears DSP filters (ears)
I can copy just about anything this side of white noise, but if I can
improve the signal, I will. :)
73 de VK3JED
http://vkradio.com
------------------------------
Message: 8
Date: Sat, 20 Sep 2008 12:35:44 +0200
From: "francesco messineo" <francesco.messineo(AT)gmail.com>
Subject: [amsat-bb] Re: Polarity questions
To: Sebastian <w4as(AT)bellsouth.net>
Cc: AMSAT BB <AMSAT-BB(AT)amsat.org>
Message-ID:
<d9f2bc20809200335t5149f4f4g802842c0f6c4b82c(AT)mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hi Sebastian,
On 9/19/08, Sebastian <w4as(AT)bellsouth.net> wrote:
> I gotta hand it to the guys who do it with a handheld, and an arrow
> antenna. I hear them all the time, they have good signals. They are
> standing up, figuring out where to point the antenna, when and where
> to turn it, up and down, sideways, and keep up with doppler, and log
> the signals and somehow also talk; I don't know how they do it!
>
I'm one of these guys :-) Even if lately I'm not much active on the
birds, since is still a good period for weak signal work.
After some practice you learn how to use all your four hands and do
things correctly HI.
By far the worst problem working birds this way is when someone wants
to chat (when in facts you can only exchange quick contacts with this
setup) and tells you that your doppler tuning isn't perfect.
Signals on birds are quite strong even with 4 elements on V and 8 on U
since you can always find the best polarization quickly and easily.
By the way, logging is easy with a recorder, I just record some time
marks at the start of the pass then I rewind at the end of the pass
and transfer all contacts on paper or whatever with the correct
time.
73
Francesco IZ8DWF (alway worked /P also as IZ5DWF and IS0FKQ).
------------------------------
Message: 9
Date: Sat, 20 Sep 2008 07:22:22 -0400
From: Lee McLamb <ku4os(AT)cfl.rr.com>
Subject: [amsat-bb] Re: Space-X to launch flight 4
To: amsat-bb(AT)amsat.org
Message-ID: <200809200722.23121.ku4os(AT)cfl.rr.com>
Content-Type: text/plain; charset="iso-8859-1"
Previously Elon had said that SpaceX had promised RazakSAT that there would be
at least one successful F1 mission before they were flown. I have not heard
of anyone else being signed up for the forth flight.
73,
Lee-KU4OS
On Friday 19 September 2008 19:14:41 G0MRF(AT)aol.com wrote:
> Hi all.
>
> I see Space X have an initial launch period scheduled for flight 4.
>
> The web site says anytime from Tuesday to Thursday (next week?) from their
> Kwajalein Atoll base in the Pacific.
>
> After the unfortunate loss of flight 3 due to a very minor glitch, does
> anyone know if the planned RazakSAT is flying of flight 4?
>
> Would be a shame if it isn't and the payload is a mass dummy only.
>
> Thanks
>
> David
>
> ( Good luck Space-X )
>
>
>
>
> _______________________________________________
> Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
------------------------------
Message: 10
Date: Sat, 20 Sep 2008 07:56:52 -0400
From: Anthony Monteiro <aa2tx(AT)comcast.net>
Subject: [amsat-bb] Re: Polarity questions
To: Clint Bradford <clintbrad4d(AT)earthlink.net>, N3TL(AT)bellsouth.net
Cc: amsat-bb(AT)amsat.org
Message-ID: <20080920115647.89KBulb00WXFW(AT)mailbox6.ucsd.edu>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 07:29 PM 9/19/2008, Clint Bradford wrote:
> >>...I have to disagree with Clint...
>
>I just must be the luckiest S.O.B.(*) working AO-51, then...During
>demonstrations in front of folks, someone in the assemblage almost
>always asks about polarization. I twist the Arrow, and we all "hear"
>no difference in its strong, clean signal.
>
>Clint, K6LCS
>909-241-7666
>
Dear Clint and friends,
There is no luck involved. The UHF downlinks on AO-51 are
circularly polarized. You can twist your Arrow all you want
and you will not hear any difference, nor could you measure
any because there isn't any difference!
The cross-polarization loss from a circular TX antenna to a
linear RX antenna is a constant 3 dB regardless of the
actual linear polarization angle.
If you want to demonstrate polarization mismatch loss, use AO-27
(which is linear) with an Arrow.
73,
Tony AA2TX
---
------------------------------
Message: 11
Date: Sat, 20 Sep 2008 11:55:53 -0400
From: "Michael Tondee" <mat_62(AT)netcommander.com>
Subject: [amsat-bb] Re: Polarity questions
To: "Edward Cole" <kl7uw(AT)acsalaska.net>
Cc: amsat-bb(AT)amsat.org
Message-ID: <009c01c91b39$5fa192c0$6500a8c0(AT)w4hij1>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Hi Ed,
I have The Satellite Experimenters Handbook, it was one of my very first
purchases when I decided to get into this. Actually that is where I got the
impression that velocity factor and electrical length of the phasing
harnesses was a big deal. Davidoff states that there can be a 10% variation
off published values from cable to cable. That is what I. thought prevented
me from building a phasing harness without proper measuring equipment. If I
can get "close enough" without a grid dip meter ot SWR anylyzer, that would
be great. I actually already have a second set of elements cut for my 70cm
antenna and I purposely left the boom long enough to accomodate them.
At any rate I wish I did have an SWR anylyzer that would cover 2 meters and
70cm but my hobby budget won't allow it at this time. I have a garden
variety 2 meter SWR bridge but nothing that works on 70 cm which is a
problem for me because I'm having trouble with the TX on the 70cm uplinks of
VO-29 and AO-7 and I suspect it's SWR related.
73,
Michael, W4HIJ
----- Original Message -----
From: "Edward Cole" <kl7uw(AT)acsalaska.net>
To: "Michael Tondee" <mat_62(AT)netcommander.com>
Cc: <amsat-bb(AT)amsat.org>
Sent: Saturday, September 20, 2008 1:59 AM
Subject: Re: [amsat-bb] Re: Polarity questions
> Michael:
>
> At 05:53 PM 9/19/2008, Michael Tondee wrote:
>>I may have misunderstood but the way I got it when I was researching
>>homebrewing yagi's for my sat station is that if you had to fix the
>>antenna
>>to either RHCP or LHCP and could not switch between the two because of
>>cost
>>or complexity or whatever other reason that your best compromise would be
>>to
>>go with linear polarization.
>
> It might be easier to wire for just one sense of CP (maybe a little
> cheaper), but the complexity is not that big a deal. You can read
> how to do it in the Satellite Experimenter's Handbook by Davidoff
> (available from Amsat or ARRL).
>
>> Feed harnesses for homebrew CP antennas are a stumbling block for me as
>> I
>>don't have a grid dip meter or SWR anylyzer to properly figure coax
>>velocity
>>and electrical length. If you don't get the phasing harnesses the right
>>length then you won't get CP anyway.
>
> You are making too much of a big deal out of this. Velocity factor
> is published by coax manufacturers so you do not need instruments to
> get close.
> 1/4 WL = Vf * 492/Fmhz in feet
> 1/4 WL (RG-213) = 0.66 * 492/144 = 2.25 feet or 27-inches
>
> If you are off 5% it will not destroy the circularity. Most hams get
> it "close enough". Of course if you are off by a quarter wavelength
> or more it will matter (20-inches at 144-MHz). I know you can get it
> within an inch and it will work fine. More accuracy produces a better
> SWR.
>
> If you plan to build much VHF and above stuff a SWR meter is a good
> basic piece of equipment to have.
>
>> I use two of the "cheap yagi" designs by Kent Britain in vertical
>>polarization and rotate them with a homebrew "SAEBRTrack" Az/El rotor box
>>and old Gemini OR-360 TV rotators. Works well enough for LEO's anyway.
>>73,
>>Michael, W4HIJ
>
> Sure, linear antennas only sacrifice 3-dB of gain in
> crosspolarization with a CP signal. Often squint angle make such
> signals elliptical so the loss can be less.
>
> GL
>
> *****************************************************
> 73, Ed - KL7UW BP40iq, 6m - 3cm
> 144-EME: FT-847, mgf-1801, 4x-xp20, 185w
> http://www.kl7uw.com AK VHF-Up Group
> NA Rep. for DUBUS: dubususa(AT)hotmail.com
> *****************************************************
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------------------------------
Message: 12
Date: Sat, 20 Sep 2008 07:51:44 -0600
From: James Duffey <JamesDuffey(AT)comcast.net>
Subject: [amsat-bb] Re: Polarity questions
To: Edward Cole <kl7uw(AT)acsalaska.net>
Cc: amsat-bb(AT)amsat.org
Message-ID: <1A3301E2-63A2-48B9-9C01-C1B9947D6BB8(AT)comcast.net>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
Yes, and the AGC in most rigs readily mask strength variations when
you are trying to judge signal strengths by ear. And once FM signals
are over the detection threshold the variation in signal strength is
difficult to discern with human hearing. - Duffey
On Sep 19, 2008, at 11:42 PM, Edward Cole wrote:
> If I may try to interpret what Clint wrote:
>
> If a yagi has 15 or 20 dB more gain than needed to receive a decent
> signal, then one can "throw away" some of that gain to cross
> polarization loss and still have enough gain to adequately receive a
> signal. Sort like saying if you have a 150-foot dish for receiving
> AO-51 it don't matter!
>
> But it "does matter" about polarization as far as maximizing
> signal. A yagi is not different than any other linear antenna in
> this respect.
>
> Now I will have a 22-element CP 2m yagi and 42-element CP 70cm yagi
> for satellites. This is obvious overkill for working the Leo
> sats. It is the old standard for mode-B sats like AO-10/13. With
> this pair you had really good signals with those old satellites. If
> and when we get another Heo, they will be appropriate for mode-UV,
> LU, US, etc. (of course this will require 1268 and 2400 antennas for
> half the link).
>
> On the HF bands polarization is generally less important because the
> ionosphere messes with polarity when the signal is
> refracted. Perhaps this is where that saying originates. If so, be
> cautious about generalizing and applying to VHF/UHF/and above! Get a
> copy of the ARRL Handbook or Antenna Book and read it. The
> information is in them. There are even better antenna texts like
> Jasik and Kraus if you like calculus.
>
> 73 Ed - KL7UW
>
> At 03:23 PM 9/19/2008, n3tl(AT)bellsouth.net wrote:
>> " ... and the polarization of the Yagi makes no difference in
>> quality of TX/RX signal."
>>
>> I know I haven't been working the satellites nearly as long as Clint
>> and many others - and with all due respect, my friend - I have to
>> disagree with the above statement. I routinely work passes during
>> which I swing my Arrow through, and sometimes beyond, 90 degrees to
>> maintain signal quality. There also have been times when a quick
>> twist of the wrist has made the difference between making a contact
>> and getting a new grid square ... and not.
>>
>> I don't-at-all disagree with the concept that working AO-27, AO-51
>> and SO-50 isn't terribly difficult with a handheld station. Frankly,
>> that has really (and pleasantly) surprised me. However, I do believe
>> that adjusting polarity when hand-holding the Arrow provides
>> improved performance during many passes.
>>
>> 73 to all,
>>
>> Tim
>>
>> -------------- Original message from Clint Bradford
>> <clintbrad4d(AT)earthlink.net>: --------------
>>
>>
>>>>> ...20-dB, assuming the signal is pure circular
>>> polarization...linear, then -3 dB...difference between RHCP and LHCP
>>> is 20 dB...difference between Horizontal and Vertical Linear is 20
>>> dB...difference between (RHCP or LHCP) and (Horizontal or
>>> Vertical) is
>>> 3 dB...the VHF/UHF Manual handbook says 20 -30dB...in the real
>>> world,
>>> expect around 20~25dB loss from being completely cross-
>>> polarized...Between linear and circular, expect about 3dB loss...
>>>
>>> Ahh, thank goodness for the engineers...
>>>
>>> Just know that to get started working the FM satellites, you do not
>>> need to spend much to make successful contacts...Working AO-51 from
>>> Southern California (which some claim is not a "real world") at a
>>> Watt
>>> or so with an HT and Arrow Antenna is a breeze, and the polarization
>>> of the Yagi makes no difference in quality of TX/RX signal.
>>>
>>> And as you refine your satellite comms requirements, you can spend
>>> more money!
>>>
>>> Clint Bradford, K6LCS
>>> 909-241-7666
>>> _______________________________________________
>>> Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the
>>> author.
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>> _______________________________________________
>> Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the
>> author.
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>
> _______________________________________________
> Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the
> author.
> Not an AMSAT-NA member? Join now to support the amateur satellite
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--
KK6MC
James Duffey
Cedar Crest NM
------------------------------
Message: 13
Date: Sat, 20 Sep 2008 11:21:01 -0400
From: Ernie <w8eh.ernie(AT)gmail.com>
Subject: [amsat-bb] Re: Polarity questions
To: amsat-bb(AT)amsat.org
Message-ID: <48D514DD.8030603(AT)gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
You won't see any polarization difference with a yagi on AO-51 because
it's downlink is circular polarized. So rotating your linear polarized
hand held yagi will make no difference in the downlink signal. This is
an ideal situation for hand held operation. :-) Now it will
make a difference in our uplink signal.
On SO-50 and AO-27, rotating your yagi to change polarization will make
a noticeable change in signal strength.
AO-51 linear uplink antenna, CIRCULAR uhf downlink antenna
SO-50 Linear uplink antenna, linear downlink antenna
AO-27 Linear uplink antenna, linear downlink antenna
Ernie W8EH
Clint Bradford wrote:
> >>...I have to disagree with Clint...
>
> I just must be the luckiest S.O.B.(*) working AO-51, then...During
> demonstrations in front of folks, someone in the assemblage almost
> always asks about polarization. I twist the Arrow, and we all "hear"
> no difference in its strong, clean signal.
>
> Clint, K6LCS
> 909-241-7666
>
> - S.O.B. - Satellite-operating Bradford
> _______________________________________________
> Sent via AMSAT-BB(AT)amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>
>
------------------------------
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End of AMSAT-BB Digest, Vol 3, Issue 474
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