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 <[email protected]> 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: [email protected] [mailto:[email protected]] 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. > >> 1. 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. > >> 2. 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 [email protected]. 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 [email protected]. 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 [email protected]. 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
