GPS "civil" frequency is 1.536 Ghz - the received signal, after
path loss is about -134dBm. 100 feet of RG/58 has about 20dB of
loss - about the most the best GPS receivers can tolerate.
Connectors and adaptors also have about 3dB insertion loss as well.
You can get get up to about 350 feet with a nice low loss cable such
as 9913.
N6RCE
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Mark Erbaugh
Sent: Monday, June 23, 2003 9:50 AM
To: tentec@contesting.com
Subject: [TenTec] GPS Antenna feedline
I received my HP Z3801 last week. To keep things on topic, the intent is to
use it as an external reference for my RX340.
I mounted the antenna over the edge of my garage roof. That was the easiest
place to get a good view of the sky. If I try to get closer to the shack, I
will have to find someone to climb on my two story roof. The supplied lead
in barely made it to the ground. I took the clock outside and hooked it up
directly to the end of the antenna. Using my laptop, I verified that all was
good. It was able to track 5 or 6 satellites and successfully completed the
survey operation (took about 3 hours).
However, I really want to install the clock in the shack. That's going to
take another 30 - 35 feet of cable. I took some spare coax jumpers and
adapters and brought the signal into the shack, but the clock wasn't able to
receive any satellites. I suspect that with all the adapters more coax than
the minimum length, I just had too much attenuation. Also, I had checked the
jumpers out for HF or 2m operation (RG-58).
Here was the arrangement
supplied lead in cable terminating in BNC - BNC / PL259 adapter - SO239
barrell connnector - 50 - 60 feet of RG58 with PL259 fittings on each end -
SO239 bulkhead fitting (to go through wall) - 25 feet of RG58 with PL259 on
one end and BNC on the other - BNC to N adapter (supplied w/ antenna ) -
clock..
Anyways, my question, what's the best way to go about extending the GPS
antenna. Since we are talking about 35 feet, I'm not adverse to buying some
more expensive coax to reduce line loss. I'll also go directly through the
wall with coax and skip the bulkhead fitting. I'd also put the N fitting
directly on the clock end of the cable. For connecting to the existing
antenna, should I cut of the existing BNC and directly splice the new
feedline (and how would that be done?), or would it be better to try and
install a matching BNC fitting and connect to the BNC already there?
Or is this a lost cause and do I need to figure out to get the antenna
closer to the shack?
73,
Mark
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