Hello All, Stating the obvious ... if one mounts the aerials as per a Wimo satellite X-Quad ... (using counterweights if necessary) ... one eliminates the crossboom problem entirely.
I've compared this kind of system against my more usual 2 x 6 + 2 x 6 homebrew array for 2m and 70cm ... (each aerial mounted at 45 degrees in relation the other) ... and correctly phased for switchable CP.
In my humble opinion, on LEO's the squint experienced just doesn't warrant the effort of being (theoretically) correct. It did make a 'slight' difference on AO-10 and AO-13 (HEO's) but still hardly worth the effort of being "technically correct".
Others may have a different opinion ... which of course, they have evey right to have.
I respect that.
73 John.
Hi John
Firstly, I am so glad to hear from you on the BB after a long time.
In my humble opinion, on LEO's the squint experienced just doesn't warrant the effort of being (theoretically) correct. It did make a
'slight'
difference on AO-10 and AO-13 (HEO's) but still hardly worth the effort of
being "technically correct".
Others may have a different opinion ... which of course, they have evey right to have.
No, I am sorry but I have to _agree_ with you! There is some time spent on squint in the bible (Martin Davidoff's superb Radio Amateur's Satellite Handbook and previously known as the Satellite Experimenter's Handbook).
What's not discussed extensively is the differences operating-wise between LEO and HEO for this phenomenon.
In practice, squint presents itself on LEOs differently to HEOs. Squint on amateur LEOs is very temporary and can largely be corrected, during a pass, by changing polarisation (H,V and/or R,L) on the fly by the operator. For HEOs, due to the increased distance and longer term power and attitude constraints, squint is usually an issue to do with the long term positioning on the satellite's downlink antenna in relation to the Earth, and unless you're a command station, and the HEO's power budget is good, you can't fix that from the ground.
For a couple of years prior to AO-40 when only LEO's (plus a tiny bit of AO-10) were running, I ran for a year or so a pair of Arrows phased on a 6' cross boom. I spent _many_ evenings messing about placing all the elements of the 70cm on one boom and all of those of the 2m on another boom but I could ever get a great match, particularly on 70cm. So I resorted to making circular polarisation work with the 2m and 70cm planes separated, and remote preamps and remote polarisation switches.
This worked _very_ well, and the gain you achieve by being able to manually switch polarisation during a null when working LEO's cannot be over emphasised IMHO.
One final point, radio amateurs have been doing antenna diversity for a very long time.
73, Howard G6LVB
Quoting Howard Long howard@howardlong.com:
[snip]
could ever get a great match, particularly on 70cm. So I resorted to making circular polarisation work with the 2m and 70cm planes separated, and remote preamps and remote polarisation switches.
This worked _very_ well, and the gain you achieve by being able to manually switch polarisation during a null when working LEO's cannot be over emphasised IMHO.
One final point, radio amateurs have been doing antenna diversity for a very long time.
73, Howard G6LVB
A contribution to the original discussion, plus a question:
I believe it was on this list that I read of an alternative to fiberglass booms (of which there are none in my local sales area). My new 10' boom comprises sched. 40 conduit with an snug-fitting 8' length of doweling placed inside. Others have removed any 'play' between the doweling and the conduit by spraying expanding foam inside the ends of the conduit. I suppose one should cap the ends, too. The total cost of this for me was CAN $20. The antennas, rotors and mast are on sawhorses now, but as far as I can see the conduit-dowel boom has an appropriate stiffness.
Now my question: Howard mentioned the much-documented advantages of polarization switching for LEO satellite work. In this same context, is it worth the additional work to include the remote logic required for V and H polarizations along with RHCP and LHCP?
73, Bruce VE9QRP
Hi Bruce
I believe it was on this list that I read of an alternative to fiberglass booms (of which there are none in my local sales area). My new 10' boom comprises sched. 40 conduit with an snug-fitting 8' length of doweling placed inside. Others have removed any 'play' between the doweling and the conduit by spraying expanding foam inside the ends of the conduit. I suppose one should cap the ends, too. The total cost of this for me was CAN $20. The antennas, rotors and mast are on sawhorses now, but as far as I can see the conduit-dowel boom has an appropriate stiffness.
I agree, this is a good way of doing it - ISTR I've seen it mentioned previously on the -BB.
Howard mentioned the much-documented advantages of polarization switching for LEO satellite work. In this same context, is it worth the additional work to include the remote logic required for V and H polarizations along with RHCP and LHCP?
It's a nice to have, but not as much as being able to switch R/LHCP. I currently use the WIMO polarisation switches and they happen to have all four polarisations built in.
73, Howard G6LVB
This has been discussed many times over the years and I still don't see why. I have been using a 10 piece of thick wall metal pipe since 1992 and never seen any problem. I have my 2 meter and 70 cm cross yagis on the ends so the pipe passes only heavy way and it works great. Since I worked AO-10 and AO-13 and later AO-40 at 30,000km I assume the metal boom is working just fine. I used the same setup at K4CQ for fieldday this past summer and came in 3rd over all. I guess folks should use what they are comfortable with. My point is it ain't that big a deal.
That is my 2 cent worth.
73's << John
On 1/10/07, Bruce Robertson broberts@mta.ca wrote:
Quoting Howard Long howard@howardlong.com:
[snip]
could ever get a great match, particularly on 70cm. So I resorted to making circular polarisation work with the 2m and 70cm planes separated, and remote preamps and remote polarisation switches.
This worked _very_ well, and the gain you achieve by being able to manually switch polarisation during a null when working LEO's cannot be over emphasised IMHO.
One final point, radio amateurs have been doing antenna diversity for a very long time.
73, Howard G6LVB
A contribution to the original discussion, plus a question:
I believe it was on this list that I read of an alternative to fiberglass booms (of which there are none in my local sales area). My new 10' boom comprises sched. 40 conduit with an snug-fitting 8' length of doweling placed inside. Others have removed any 'play' between the doweling and the conduit by spraying expanding foam inside the ends of the conduit. I suppose one should cap the ends, too. The total cost of this for me was CAN $20. The antennas, rotors and mast are on sawhorses now, but as far as I can see the conduit-dowel boom has an appropriate stiffness.
Now my question: Howard mentioned the much-documented advantages of polarization switching for LEO satellite work. In this same context, is it worth the additional work to include the remote logic required for V and H polarizations along with RHCP and LHCP?
73, Bruce VE9QRP _______________________________________________ Sent via AMSAT-BB@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
As a reasonably long time licensed ham (40 years), but very new to satellites, I would like to ask the brain trust whether CP antennas are really needed. I am ready to buy a set, but in poking around the net, I found this exchange by Mike , K6MYC, about not using CP antennas:
Look at http://www.qth.com/ka9fox/ant-nest.txt
Look towards the bottom, and Mike's replies are in caps.
I do not have the real estate for separate 144/432 antennas for terrestrial and sat. I have the az/el rotors.
So whats the thought on this? Should I just go with a pair of H-pol beams and leave well enough alone, or should I go with the CP antennas?
Tom Bosscher K8TB
Hi Tom
As a reasonably long time licensed ham (40 years), but very new to satellites, I would like to ask the brain trust whether CP antennas are really needed. I am ready to buy a set, but in poking around the net, I found this exchange by Mike , K6MYC, about not using CP antennas:
Look at http://www.qth.com/ka9fox/ant-nest.txt
Look towards the bottom, and Mike's replies are in caps.
I do not have the real estate for separate 144/432 antennas for terrestrial and sat. I have the az/el rotors.
So whats the thought on this? Should I just go with a pair of H-pol beams and leave well enough alone, or should I go with the CP antennas?
I may have misubderstood, but it looks like Mike is saying use two stacked yagis in the same linear polarisation instead of one CP antenna.
My practical experiences don't agree with Mike's.
Having polarisation switching on LEOs in my opinion is worth several dB more than doubling your boom length or stacking.
If I had a pair of linear yagis and did not want to go CP, I would mount them orthogonally and switch between them during the pass to avoid nulls.
73, Howard G6LVB
At 01:10 PM 1/11/2007, Howard Long wrote:
Having polarisation switching on LEOs in my opinion is worth several dB more than doubling your boom length or stacking.
Being a portable operator and having used polarisation rotation (the advantage of having the antenna in one's hand), I agree that the ability to compensate for polarisation shifts, whether by hand rotating a LP antenna, using CP antennas or switching between two orthogonal LP antennas is a huge advantage for working LEOs.
If I had a pair of linear yagis and did not want to go CP, I would mount them orthogonally and switch between them during the pass to avoid nulls.
Agreed.
73 de VK3JED http://vkradio.com
I homebrewed my antennas and it wouldn't have been that big a deal to make crossed yagi's for CP as far as the mechanical end of it went but for my first attempts at satellite, I went with linear polarization just for simplicity's sake. I do ok with them on LEO's but since I've never had the CP, I can't make a quantitive comparison. My biggest stumbling block with CP was figuring the length of phasing harnesses and such because I don't have the equipment to do so. Of course, if you're buying a set, I suppose all that's done for you. 73, Michael W4HIJ K8TB wrote:
As a reasonably long time licensed ham (40 years), but very new tosatellites, I would like to ask the brain trust whether CP antennas are really needed. I am ready to buy a set, but in poking around the net, I found this exchange by Mike , K6MYC, about not using CP antennas:
Look at http://www.qth.com/ka9fox/ant-nest.txt
Look towards the bottom, and Mike's replies are in caps.
I do not have the real estate for separate 144/432 antennas for terrestrial and sat. I have the az/el rotors.
So whats the thought on this? Should I just go with a pair of H-pol beams and leave well enough alone, or should I go with the CP antennas?
Tom Bosscher K8TB
Sent via AMSAT-BB@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
participants (7)
-
Bruce Robertson -
Howard Long -
john hackett -
John Price -
K8TB -
Michael Tondee -
Tony Langdon