[time-nuts] GPS Antenna Voltage-Dropping
darren.storer at gmail.com
Fri Sep 4 01:49:11 UTC 2009
the model of bias tee referenced below works well, with very low insertion
loss, down towards 1GHz, despite the manufacturer's specifications:
Item #270287524274 on a well known Internet auction site, lists the
"Buy-It-Now" price as $19.95 for brand new units. If you are worried about
return loss, I can provide plots for GPS frequencies. Performance really
falls off below 500MHz, where the insertion losses approach 50dB!
For the money, the build quality is superb.
PS. I have no commercial interest in the sale of the items; I'm just a happy
2009/9/3 <GandalfG8 at aol.com>
> In a message dated 03/09/2009 17:04:50 GMT Daylight Time,
> warrensjmail-one at yahoo.com writes:
> Seems like a good idea, a lot simpler and cleaner than the other
> Sounds like a data problem, I'd suspect your VSWR meter or cabling first.
> Maybe your VSWR meter does not like diodes especially if it is not running
> current thru them.
> And if you are running current thru them to approximate the GPS antenna,
> whatever you're doing to run the current thru them is making the reading
> Did you try just the BNC adapter with just a short inside? And with just
> the cap inside? Better cap?
> And the finial test does it work OK despite the VSWR reading?
> Not really a very good idea, we're talking about two silicon diodes in
> series with each other and then used as the central conductor of a coax
> at nearly 1600MHz.
> Aside from the discontinuity caused at the diode junction itself, consider
> how fine the wire might be inside that diode and consider the magnitude of
> the uncompensated impedance changes caused by this, the high VSWR shouldn't
> come as too much of a surprise.
> Then consider what two rectifying diode junctions are going to do to your
> RF signal regardless of the VSWR.
> Burt's suggestion of fitting the diodes inside the antenna stands more
> chance of success, assuming they are fitted correctly, but I would still
> suggest an external biased T as the most practical answer if one still
> on using the 3.6v antenna.
> With 5v antennas so widely available though there really doesn't seem to be
> much good reason for doing this anyway.
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