First, almost every mag mount will scratch your car - something never printed on the packaging.
Second, any "vertical" antenna for the V/U FM sats will have a transmission (and generally receive pattern) that is perpendicular to its mast. So, think about it: A GREAT pass of 90 degrees goes overhead - your vertical is valueless during the middle of that great pass.
SO ... Some are "compensating" by purchasing better antennas (i.e., more gain) and pumping out 20 or 50 or 100W. Awful wasteful, IMHO - since we both know we're workin' these birds with a Watt or two.
Ideally - in a car - I would think that stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. I have a Larsen KG-2/70-CX-PL whose whip I can adjust about 20 degrees off normal, and hopefully be travelling in the correct direction to work a bird or two.
But if you're going to stop and park - then just whip out your homebrew Tape Measure Beam from the trunk, and REALLY make some contacts!
BUT - You told me you wanted to keep moving with the familt in the car. So ...
Then maybe a Larsen mag mount - which you can purchase an extra whip. And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent.
Keep extra allen keys in the glove compartment - to loosen and re-position the whip. You might look a little funny driving down the road with a "bent whip." But you'll be more successful with the FM birds!
Got kids who are on the 'Net already? Plan your rest stops/meal stops/bathroom breaks around the satellite passes! Give 'em maps ... sat pass times ... have 'em figure out approximately where they'll be at what time ... Sure beats having them play video games or watch TV in the back ... (grin)
Suggested items:
Larsen NMO-MM-R-BNC - a solid, round mag mount with NMO connector for an antenna. This particular one terminates in a BNC-MALE. They have other models terminating in other connectors. Or get one that terminates in the FME system, and you can then purchase adapters for SMA, BNC, PL - whatever.
Larsen NMO-2/70 BLACK - very good dual-band NMO base whip.
Larsen W270B - just the replacement whip.
HRO carries all this. Snag the Larsen Amateur Products .pdf catalog at ...
http://www.larsen-antennas.com/catalogs_main.shtml
Clint, K6LCS 909-241-7666
Everyone's comments are correct and valid within their context. But the original question was optimizing for the casual mobile operator in motion. So here are some additional considerations...
Second, any "vertical" antenna...will have a [null overhead] So, think about it: A GREAT pass of 90 degrees goes overhead your vertical is valueless during the middle of that great pass.
True, but when we put some actual numbers on that, the loss is quite insignificant. Using AO51, only one pass every 5 days goes above 82 degrees, and the total duration above 82 degrees is 24 seconds, out of all in view times. So we agree, the antenna is valueless, but for under 1% of the time. The tradeoff is that it is 3 dB better most of the rest of the time...
The measured elevation profile of a 3/4 wave vertical (a 19.5" whip on the 435 downlink) is shown 80% down the page http://aprs.org/astars.html. The overhead null is only 10 dB down at 82 degrees... BUT the satellite is 10 dB closer at that point, so you still hear it almost the same as when it came above 25 degrees. So you get full sky coverage above 25 degrees > 99% of the time with the vertical.
Ideally - in a car - ... stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. Then maybe a Larsen mag mount... And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent. you'll be more successful with the FM birds!
Yes, good idea, but now there is some directionality and so the car needs to remain pointed towards the satellite during the pass. Otherwise there is still the null, it is just in a different part of the sky.
- If the satellite is circular polarization the 19.5 " whip looses 3 dB
of gain.
Yes, but most people have observed a polarization shift during overhead passes. And in that case, the loss of a circularized antenna is much worse than 3 dB... usually a complete fade. SO I agree, a circular antenna gets 3 dB better half the time, and much worse the other half the time. I prefer the simplicity of the whip that does not give up more than 3dB no matter what the polarization is. Mounting a quadrifilar on the roof of the mobile is also problematic.
- The common Quadrifilar Antenna is 1/2 wave 1/2 turn.
The 1 wavelength, 1 turn Quadrifilar Antenna has its highest gain near or at the horizon depending on the length to diameter ratio.
But it is still only a 3 dB gain antenna out there, and so it is not going to hear the satellite down on the horizon anyway because the satellite is 10 dB farther away and usually blocked for the mobile. So having gain on the horizon for a mobile omni antenna is wasted. It either is not enough or it creats additional nulls higher up. Better to move that gain higher up but smooth where the satellite is closer and then have good contacts, than waste gain where it is already insufficient or problematic.
Just different perspectives, but the devil is in the details...
Bob, Wb4APR
Very interesting info...
I'm thinking maybe putting a mag mount with 19.5" of nice shiny wire on a pizza pan would do as well as the Arrow (I hate the Arrow, even on a tripod!)
73, Ted, K7TRK
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob Bruninga Sent: Thursday, September 15, 2011 8:52 AM To: 'AMSAT BB' Subject: [amsat-bb] Re: Which Mobile Mag Mount?
Everyone's comments are correct and valid within their context. But the original question was optimizing for the casual mobile operator in motion. So here are some additional considerations...
Second, any "vertical" antenna...will have a [null overhead] So, think about it: A GREAT pass of 90 degrees goes overhead your vertical is valueless during the middle of that great pass.
True, but when we put some actual numbers on that, the loss is quite insignificant. Using AO51, only one pass every 5 days goes above 82 degrees, and the total duration above 82 degrees is 24 seconds, out of all in view times. So we agree, the antenna is valueless, but for under 1% of the time. The tradeoff is that it is 3 dB better most of the rest of the time...
The measured elevation profile of a 3/4 wave vertical (a 19.5" whip on the 435 downlink) is shown 80% down the page http://aprs.org/astars.html. The overhead null is only 10 dB down at 82 degrees... BUT the satellite is 10 dB closer at that point, so you still hear it almost the same as when it came above 25 degrees. So you get full sky coverage above 25 degrees > 99% of the time with the vertical.
Ideally - in a car - ... stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. Then maybe a Larsen mag mount... And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent. you'll be more successful with the FM birds!
Yes, good idea, but now there is some directionality and so the car needs to remain pointed towards the satellite during the pass. Otherwise there is still the null, it is just in a different part of the sky.
- If the satellite is circular polarization the 19.5 " whip looses 3 dB
of gain.
Yes, but most people have observed a polarization shift during overhead passes. And in that case, the loss of a circularized antenna is much worse than 3 dB... usually a complete fade. SO I agree, a circular antenna gets 3 dB better half the time, and much worse the other half the time. I prefer the simplicity of the whip that does not give up more than 3dB no matter what the polarization is. Mounting a quadrifilar on the roof of the mobile is also problematic.
- The common Quadrifilar Antenna is 1/2 wave 1/2 turn.
The 1 wavelength, 1 turn Quadrifilar Antenna has its highest gain near or at the horizon depending on the length to diameter ratio.
But it is still only a 3 dB gain antenna out there, and so it is not going to hear the satellite down on the horizon anyway because the satellite is 10 dB farther away and usually blocked for the mobile. So having gain on the horizon for a mobile omni antenna is wasted. It either is not enough or it creats additional nulls higher up. Better to move that gain higher up but smooth where the satellite is closer and then have good contacts, than waste gain where it is already insufficient or problematic.
Just different perspectives, but the devil is in the details...
Bob, Wb4APR
_______________________________________________ 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
I'm thinking maybe putting a mag mount with 19.5" of nice shiny wire on a pizza pan would do as well as the Arrow..
The pizza pan is assumed to be the size of your car roof to get the full gain of the 3/4 wave vertical. Also, if you have the arrow, then you can more than double your contact time because you can point it low on the horizon.
The 19.5" whip in the center of your car roof is the no-muss-no-fuss approach, for operating while mobile, but it does not compare to having a good beam.
Bob, Wb4APR
73, Ted, K7TRK
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob Bruninga Sent: Thursday, September 15, 2011 8:52 AM To: 'AMSAT BB' Subject: [amsat-bb] Re: Which Mobile Mag Mount?
Everyone's comments are correct and valid within their context. But the original question was optimizing for the casual mobile operator in motion. So here are some additional considerations...
Second, any "vertical" antenna...will have a [null overhead] So, think about it: A GREAT pass of 90 degrees goes overhead your vertical is valueless during the middle of that great pass.
True, but when we put some actual numbers on that, the loss is quite insignificant. Using AO51, only one pass every 5 days goes above 82 degrees, and the total duration above 82 degrees is 24 seconds, out of all in view times. So we agree, the antenna is valueless, but for under 1% of the time. The tradeoff is that it is 3 dB better most of the rest of the time...
The measured elevation profile of a 3/4 wave vertical (a 19.5" whip on the 435 downlink) is shown 80% down the page http://aprs.org/astars.html. The overhead null is only 10 dB down at 82 degrees... BUT the satellite is 10 dB closer at that point, so you still hear it almost the same as when it came above 25 degrees. So you get full sky coverage above 25 degrees > 99% of the time with the vertical.
Ideally - in a car - ... stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. Then maybe a Larsen mag mount... And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent. you'll be more successful with the FM birds!
Yes, good idea, but now there is some directionality and so the car needs to remain pointed towards the satellite during the pass. Otherwise there is still the null, it is just in a different part of the sky.
- If the satellite is circular polarization the 19.5 " whip looses 3 dB
of gain.
Yes, but most people have observed a polarization shift during overhead passes. And in that case, the loss of a circularized antenna is much worse than 3 dB... usually a complete fade. SO I agree, a circular antenna gets 3 dB better half the time, and much worse the other half the time. I prefer the simplicity of the whip that does not give up more than 3dB no matter what the polarization is. Mounting a quadrifilar on the roof of the mobile is also problematic.
- The common Quadrifilar Antenna is 1/2 wave 1/2 turn.
The 1 wavelength, 1 turn Quadrifilar Antenna has its highest gain near or at the horizon depending on the length to diameter ratio.
But it is still only a 3 dB gain antenna out there, and so it is not going to hear the satellite down on the horizon anyway because the satellite is 10 dB farther away and usually blocked for the mobile. So having gain on the horizon for a mobile omni antenna is wasted. It either is not enough or it creats additional nulls higher up. Better to move that gain higher up but smooth where the satellite is closer and then have good contacts, than waste gain where it is already insufficient or problematic.
Just different perspectives, but the devil is in the details...
Bob, Wb4APR
_______________________________________________ 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
Bob, thanks for the great data.
Question: do you think your data/techniques have any application to using a dual band HT with a long whip (e.g. Diamond SRH77CA - 15.5"long)
In other words would you be better off just holding the HT vertical and fairly stationary during the pass (adjusting Doppler of course) or moving the darn thing all over until you capture the bird. I realize it is not duplex, etc. but it does seem to work on a strong pass. I just can't figure out the best way to hold the radio
Thanks for any help
73, Ted, K7TRK
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob Bruninga Sent: Thursday, September 15, 2011 8:52 AM To: 'AMSAT BB' Subject: [amsat-bb] Re: Which Mobile Mag Mount?
Everyone's comments are correct and valid within their context. But the original question was optimizing for the casual mobile operator in motion. So here are some additional considerations...
Second, any "vertical" antenna...will have a [null overhead] So, think about it: A GREAT pass of 90 degrees goes overhead your vertical is valueless during the middle of that great pass.
True, but when we put some actual numbers on that, the loss is quite insignificant. Using AO51, only one pass every 5 days goes above 82 degrees, and the total duration above 82 degrees is 24 seconds, out of all in view times. So we agree, the antenna is valueless, but for under 1% of the time. The tradeoff is that it is 3 dB better most of the rest of the time...
The measured elevation profile of a 3/4 wave vertical (a 19.5" whip on the 435 downlink) is shown 80% down the page http://aprs.org/astars.html. The overhead null is only 10 dB down at 82 degrees... BUT the satellite is 10 dB closer at that point, so you still hear it almost the same as when it came above 25 degrees. So you get full sky coverage above 25 degrees > 99% of the time with the vertical.
Ideally - in a car - ... stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. Then maybe a Larsen mag mount... And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent. you'll be more successful with the FM birds!
Yes, good idea, but now there is some directionality and so the car needs to remain pointed towards the satellite during the pass. Otherwise there is still the null, it is just in a different part of the sky.
- If the satellite is circular polarization the 19.5 " whip looses 3 dB
of gain.
Yes, but most people have observed a polarization shift during overhead passes. And in that case, the loss of a circularized antenna is much worse than 3 dB... usually a complete fade. SO I agree, a circular antenna gets 3 dB better half the time, and much worse the other half the time. I prefer the simplicity of the whip that does not give up more than 3dB no matter what the polarization is. Mounting a quadrifilar on the roof of the mobile is also problematic.
- The common Quadrifilar Antenna is 1/2 wave 1/2 turn.
The 1 wavelength, 1 turn Quadrifilar Antenna has its highest gain near or at the horizon depending on the length to diameter ratio.
But it is still only a 3 dB gain antenna out there, and so it is not going to hear the satellite down on the horizon anyway because the satellite is 10 dB farther away and usually blocked for the mobile. So having gain on the horizon for a mobile omni antenna is wasted. It either is not enough or it creats additional nulls higher up. Better to move that gain higher up but smooth where the satellite is closer and then have good contacts, than waste gain where it is already insufficient or problematic.
Just different perspectives, but the devil is in the details...
Bob, Wb4APR
_______________________________________________ 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
Ted,
Regarding antenna orientation for handhelds, see the picture associated with item #6 at this web page: http://www.amsat.org/amsat-new/echo/EchoHT.php
Check this video out, too, for inspiration: http://www.youtube.com/watch?v=FCFWrXzdgeM
When using an HT whip, the trick I use is to avoid any sudden movement or adjustment of the antenna once you have a decent copy of the downlink. Even then, it can be challenging as you will need to track the bird. I own some of the commonly recommended antennas such as the Pryme AL800. I don't own the Diamond you referenced but I have a similar Comet SMA24 that is useable, albeit not ideal, for AO-51. My experience has been that the "cat whisker" style whips tend to have too much movement. I might try to make a video to demonstrate this effect.
Even with a stock rubber dummy load, I can hear many passes of AO-51 and some overhead AO-27 passes.
K6LCS' web page has some good recommendations: http://web.me.com/clintbradford/Work-Sat/Antennas.html
I recommend the AL800 and similar. I personally am most pleased with cost and function of the Smiley 270A, which at $22 is a real bargain. After some passes with this antenna used, I have listened to the recording and been unable to distinguish my HT performance from that of a full-bore home satellite station. Again, there are limitations but it is a lot of fun to try!
73 Clayton W5PFG
On Thu, Sep 15, 2011 at 6:40 PM, Ted k7trkradio@charter.net wrote:
Bob, thanks for the great data.
Question: do you think your data/techniques have any application to using a dual band HT with a long whip (e.g. Diamond SRH77CA - 15.5"long)
In other words would you be better off just holding the HT vertical and fairly stationary during the pass (adjusting Doppler of course) or moving the darn thing all over until you capture the bird. I realize it is not duplex, etc. but it does seem to work on a strong pass. I just can't figure out the best way to hold the radio
Thanks for any help
73, Ted, K7TRK
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob Bruninga Sent: Thursday, September 15, 2011 8:52 AM To: 'AMSAT BB' Subject: [amsat-bb] Re: Which Mobile Mag Mount?
Everyone's comments are correct and valid within their context. But the original question was optimizing for the casual mobile operator in motion. So here are some additional considerations...
Second, any "vertical" antenna...will have a [null overhead] So, think about it: A GREAT pass of 90 degrees goes overhead your vertical is valueless during the middle of that great pass.
True, but when we put some actual numbers on that, the loss is quite insignificant. Using AO51, only one pass every 5 days goes above 82 degrees, and the total duration above 82 degrees is 24 seconds, out of all in view times. So we agree, the antenna is valueless, but for under 1% of the time. The tradeoff is that it is 3 dB better most of the rest of the time...
The measured elevation profile of a 3/4 wave vertical (a 19.5" whip on the 435 downlink) is shown 80% down the page http://aprs.org/astars.html. The overhead null is only 10 dB down at 82 degrees... BUT the satellite is 10 dB closer at that point, so you still hear it almost the same as when it came above 25 degrees. So you get full sky coverage above 25 degrees > 99% of the time with the vertical.
Ideally - in a car - ... stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. Then maybe a Larsen mag mount... And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent. you'll be more successful with the FM birds!
Yes, good idea, but now there is some directionality and so the car needs to remain pointed towards the satellite during the pass. Otherwise there is still the null, it is just in a different part of the sky.
- If the satellite is circular polarization the 19.5 " whip looses 3 dB
of gain.
Yes, but most people have observed a polarization shift during overhead passes. And in that case, the loss of a circularized antenna is much worse than 3 dB... usually a complete fade. SO I agree, a circular antenna gets 3 dB better half the time, and much worse the other half the time. I prefer the simplicity of the whip that does not give up more than 3dB no matter what the polarization is. Mounting a quadrifilar on the roof of the mobile is also problematic.
- The common Quadrifilar Antenna is 1/2 wave 1/2 turn.
The 1 wavelength, 1 turn Quadrifilar Antenna has its highest gain near or at the horizon depending on the length to diameter ratio.
But it is still only a 3 dB gain antenna out there, and so it is not going to hear the satellite down on the horizon anyway because the satellite is 10 dB farther away and usually blocked for the mobile. So having gain on the horizon for a mobile omni antenna is wasted. It either is not enough or it creats additional nulls higher up. Better to move that gain higher up but smooth where the satellite is closer and then have good contacts, than waste gain where it is already insufficient or problematic.
Just different perspectives, but the devil is in the details...
Bob, Wb4APR
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
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
I just can't figure out the best way to hold the radio
By all means, you hold the radio to whatever works best. That is a MANY dB advanatage over fixed antnenas, because the human ear-hand-feedback system can respond in fractions of a second to always maintain the best signal at any instant to match the instantaneous polarization of the satelite. No mechanical mounting can do that.
Bob
-----Original Message----- From: Ted [mailto:k7trkradio@charter.net] Sent: Thursday, September 15, 2011 7:41 PM To: 'Bob Bruninga'; 'AMSAT BB' Subject: RE: [amsat-bb] Re: Which Mobile Mag Mount?
Bob, thanks for the great data.
Question: do you think your data/techniques have any application to using a dual band HT with a long whip (e.g. Diamond SRH77CA - 15.5"long)
In other words would you be better off just holding the HT vertical and fairly stationary during the pass (adjusting Doppler of course) or moving the darn thing all over until you capture the bird. I realize it is not duplex, etc. but it does seem to work on a strong pass. I just can't figure out the best way to hold the radio
Thanks for any help
73, Ted, K7TRK
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob Bruninga Sent: Thursday, September 15, 2011 8:52 AM To: 'AMSAT BB' Subject: [amsat-bb] Re: Which Mobile Mag Mount?
Everyone's comments are correct and valid within their context. But the original question was optimizing for the casual mobile operator in motion. So here are some additional considerations...
Second, any "vertical" antenna...will have a [null overhead] So, think about it: A GREAT pass of 90 degrees goes overhead your vertical is valueless during the middle of that great pass.
True, but when we put some actual numbers on that, the loss is quite insignificant. Using AO51, only one pass every 5 days goes above 82 degrees, and the total duration above 82 degrees is 24 seconds, out of all in view times. So we agree, the antenna is valueless, but for under 1% of the time. The tradeoff is that it is 3 dB better most of the rest of the time...
The measured elevation profile of a 3/4 wave vertical (a 19.5" whip on the 435 downlink) is shown 80% down the page http://aprs.org/astars.html. The overhead null is only 10 dB down at 82 degrees... BUT the satellite is 10 dB closer at that point, so you still hear it almost the same as when it came above 25 degrees. So you get full sky coverage above 25 degrees > 99% of the time with the vertical.
Ideally - in a car - ... stopping and parking and getting a vertical perpendicular to the orbit of the satellite would give best results. Then maybe a Larsen mag mount... And bend - er, I mean, "re-form" that whip right at the base so that it is about 20" bent. you'll be more successful with the FM birds!
Yes, good idea, but now there is some directionality and so the car needs to remain pointed towards the satellite during the pass. Otherwise there is still the null, it is just in a different part of the sky.
- If the satellite is circular polarization the 19.5 " whip looses 3 dB
of gain.
Yes, but most people have observed a polarization shift during overhead passes. And in that case, the loss of a circularized antenna is much worse than 3 dB... usually a complete fade. SO I agree, a circular antenna gets 3 dB better half the time, and much worse the other half the time. I prefer the simplicity of the whip that does not give up more than 3dB no matter what the polarization is. Mounting a quadrifilar on the roof of the mobile is also problematic.
- The common Quadrifilar Antenna is 1/2 wave 1/2 turn.
The 1 wavelength, 1 turn Quadrifilar Antenna has its highest gain near or at the horizon depending on the length to diameter ratio.
But it is still only a 3 dB gain antenna out there, and so it is not going to hear the satellite down on the horizon anyway because the satellite is 10 dB farther away and usually blocked for the mobile. So having gain on the horizon for a mobile omni antenna is wasted. It either is not enough or it creats additional nulls higher up. Better to move that gain higher up but smooth where the satellite is closer and then have good contacts, than waste gain where it is already insufficient or problematic.
Just different perspectives, but the devil is in the details...
Bob, Wb4APR
_______________________________________________ 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 (4)
-
Bob Bruninga -
Clayton Coleman W5PFG -
Clint Bradford -
Ted