[time-nuts] GPS Antenna Voltage-Dropping

Storer, Darren 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
> suggestions.
> 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
> unhappy.
> 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?
> -----------------------
> Ummmmm
> 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
> adapter
>  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
> insists
> 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.
> regards
> Nigel
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