[time-nuts] "Better" gps antennas than a Symmetricom 58532A
Magnus Danielson
magnus at rubidium.dyndns.org
Wed Jan 23 14:09:25 EST 2013
On 01/23/2013 03:59 PM, John Lofgren wrote:
>
> < snip>
> And it's not clear that there's actually "loss" due to mismatch. Most
> antennas/preamps/receivers don't have exactly 50 ohm impedances. 75/50
> is only 1.5:1, and there's an awful lot of antennas and receivers out
> there that only claim 2:1 VSWR. The usual spec for the antenna is
> 1.5:1, so for all you know the Antenna and Receiver is already 75 ohms,
> and RG6 will give you a better match than 50 ohm LMR400.
> < snip>
>
> An excellent point. A similar issue is the connectors. If you read the data sheets for many common connectors and adapters you'll find that a lot of them are only rated for a 1.2:1 VSWR. I ran into this issue a few years ago when trying to measure reflection coefficient in a system using TNC connectors. It turned out that the connectors set the VSWR limit, not the test of the measuring system.
Should I make it a habbit of TDRing my GPS antennas, receivers and
splitters?
Cheers,
Magnus
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