[amsat-bb] Re: Good mobile antennas to use
bruninga at usna.edu
Wed Sep 14 19:31:12 PDT 2011
>> The problem is hearing the downlink. That is
>> why the 19.5" whip is so good... and has
>> almost 7dBi gain above 30 degrees up to over 70.
>> So it beats a quadrifilar easily...
> As an example, my last four AO-51 passes were
> 36, 15, 26, and 27 degrees -max- elevation.
> Would you prefer gain at low to mid elevations,
> or above 30 degrees to work this satellite today?
We need to be careful to not bring pears and pommegranets into the apples and oranges comparisons...
Were those 15 to 27 degree passes done with a Quadrifiliar on the downlink? We need to keep comparisons to apples and apples or oranges to oranges.. not all the other possibilities.
> A 1/4 wave will work, sometimes, but it is far
> from ideal for anything but occasional downlink
True, It limits operation to passes above say about 25 degrees, and that does limit you to 2 or 3 passes per day, but at least they will be GOOD passes that you can hear well with smooth performance across the sky above that while mobile and with no pointing cappability. (except for a very rare direct overhead pass above 80 degrees once in a blue moon) which lasts for less than a minute..
> As Clayton pointed out, it's easy to spot the
> guys on crappy antennas, as they are the ones
> missing calls, or transmitting on top of QSOs,
> because they mistake a loss of signal as a
> break in the action.
What Clayton referred to were not simple 1/4 wave verticals. He was referring to standard "mobile" antennas that have gain on the horizon and *guaranteed* nulls then between about 10 to 40 degrees (the primary satellite operating range) or so plus the small null overhead. By mentioning the fades, he was clearly referring to these standard gain antennas. By definition, a gain mobile antenna has multiple nulls between the horizon and overhead thus really playing havoc with satellitie contacts. And that is precisely why a standard mobile GAIN antenna is well known to be *no-good* for satellite work.
But this is not what a 19.5" whip does. The 1/4 (3/4) wave 19.5" whip does not have gain on the horizon (so it is rarely used for terrestrial mobile) but its pattern is ideal for satellite work on high passes. It does NOT then have a null in its pattern that causes the "crappy" contacts, and it does have plenty of gain above about 25 degrees.... and it is a smooth pattern.... not like the multi lobes of a standard mobile gain antenna.
> PS My satellite grid addiction started in 2000
> with a DR-605 Alinco and a 1/4 wave magmount, ...
> Since then I've operated mobile from probably
> 100+ grids on the FM and SSB birds both.
> It's addictive.
Yes, I think we are actually agreeing. A 1/4 wave 19.5" vertical works well. But a common mobile gain antenna *does not*. There is a big difference.
More information about the AMSAT-BB