From jimr@maia.usno.navy.mil Mon Jan 25 15:59:20 EST 1999
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From: Jim Ray (USNO 202-762-1444)
Message-Id: <199901252057.PAA13370@maia.usno.navy.mil>
Subject: Cable spec information
To: gpst@maia.usno.navy.mil
Date: Mon, 25 Jan 1999 15:57:28 EST
X-Mailer: Elm [revision: 212.4]
Status: RO
For consideration in choosing an RF cable from a GPS antenna to the
receiver, the following information concerning cable specs was obtained
from Edward Manzanares at UNAVCO. Ed's main
consideration was signal attenuation and the 3 types he recommends
are very good from this perspective. For timing applications,
temperature stability is also a concern. I have inserted into Ed's
text the specs from Andrews for the total electrical length change
(in PPM/C) due to temperature variation over the range -30 C to
+40 C. These specs were obtained from the Andrew Corp. web site
given below.
For comparison, the Andrew FSJ1-50A installed at USNO last year has
a loss at 1250 MHz of 6.77 dB/100 foot and a loss at 1500 MHz of
7.47 dB/100 foot -- significantly greater than the 3 LDF cables
Ed describes below. The sensitivity of the FSJ1-50A electrical
length to temperature changes varies between -7 PPM/C and +9 PPM/C,
which is a somewhat great range than the LDF types but FSJ1-50A has
a coefficient approximately zero around 20 C. By contrast, the
temperature sensitivities for RG cable types, which are commonly
used, are much larger.
--Jim
-------------------------------------------------------------------------
>From manz@unavco.ucar.edu Wed Nov 18 15:09:09 EST 1998
Date: Wed, 18 Nov 1998 13:08:12 -0700
From: Edward Manzanares
To: kogan@ldeo.columbia.edu, jimr@maia.usno.navy.mil
Subject: Low-loss antenna cable
Hello Misha and Jim,
Barb Perin asked me to send you some information on low loss antenna
cables. We recommend using heliax cable for any distance over 100ft
(30m). We purchase the heliax from the following vendor:
Andrew Corporation
10500 W. 153rd Street
Orland Park, IL 60462
Tel: 1-800-255-1479
Internet: http://www.andrew.com
[specs and guides for Heliax coaxial cables are at
http://www.andrew.com/products/heliax/catalog37.asp]
There are three types of heliax cable that work well at the 1.26GHz and
1.6GHz range:
1) LDF4-50A cable. This cable has about a 2.96db loss per 100 feet
at 1.6GHz and 2.6db loss per 100 feet at 1.26GHz. This cable costs
$2.55 per foot. [+7 PPM/C to +16 PPM/C over -30 to +40 C]
2) LDF5-50A cable. This cable has about a 1.67db loss per 100 feet
at 1.6GHz and 1.5db loss per 100 feet at 1.26GHz. This cable costs
$5.85 per foot. [+5 PPM/C to +12 PPM/C over -30 to +40 C]
3) LDF6 cable. This cable has about a 1.45db loss per 100 feet
at 1.6GHz and 1.2db loss per 100 feet at 1.26GHz. The cost of this
cable is $11.15 per foot. [temp coefficients not available]
Which cable works best depends on the distance between the antenna and
receiver and what type of receiver is being used.
Please contact me if you have any questions. You may want to also
contact Andrew Corporation for further information. I will also check
on temp. ratings for these cables.
Ed