The GPS frequency is 1575.42 MHz. Line loss for 50 feet of RG58 at this frequency is around 10 dB. RG58 is not really recommended for microwaves! 

Jim Hannon

---------- Original Message ----------------------------------
From: "Geoffrey" 
Reply-To: psn-l@..............
Date:  Tue, 23 May 2006 10:42:56 -0700

>Can you tell me the frequency traveling
>in the coaxial cable ?
>
>According to the 2004 ARRL handbook your losses
>in an RG8 cable with foam insulation at
>100MHz will be about 1.7db per 100 feet of cable
>500MHz will be about 4db per 100 feet
>if you are using some other kind of dielectric
>the losses might be almost twice that.
>
>the velocity factor varies according to
>the manufacturer but varies somewhere
>between 82% and 86% speed of light
>for cables with outside diameters in the range of
>0.2 - 0.24 inches. You can use this number to trim
>the cable to the proper multiple ot partial multiple
>of a wavelength.
>
>I have found RG8 to be the best cable to use
>when connecting the front end of a receiver
>directly to an antenna.
>
>Most antennas have a very low impedance
>50 ohms or less in the case of Yagi-Uda.
>
>You can match impedance's using various techniques
>and you can place ferrite beads near both ends of the cable
>to isolate signals on the outside/inside of the shield.
>
>The study of antennas and transmission lines
>is everybit as interesting as seismology itself.
>What is a geophone but a kind of electro mechanical antenna.
>
>
>----- Original Message ----- 
>From: "Stephen & Kathy" 
>To: 
>Sent: Monday, May 22, 2006 6:49 PM
>Subject: Re: Extending coax on Motorola Oncore GPS antenna
>
>
>> Hi,,  I simply clipped the antenna cable close to the antenna and 
>> soldered RG58U (what ever the 50 ohm number is), cable to it!   I used a 
>> short piece of the RG58 interior insulation and sloped it to match the 
>> 174 to cover the solder connection, then folded the outside conductor, 
>> from each cable, over it, taped it, and waterproofed it!!  About 10 feet 
>> went up the pole where the antenna sits,, about 10 feet went through the 
>> attic with about a foot down from the ceiling where it is connected to 
>> the GPS, (GPS is still indoors), then about 30 feet of RS232 to the 
>> computer!  I use telephone cable and connectors for the GPS power and 
>> one second data!  I get strong satellite signals, even with the cable 
>> diameter mismatch!
>> 
>> Just my two cents worth of experience!!
>> 
>>  Stephen
>>  PSN Station #55
>>  near Pilot Hill Ca. USA
>>  38.828N  120.979W
>> 
>> apsn wrote:
>>> OR, has anyone moved their Motorola Oncore GPS engine and antenna to a 
>>> remote spot (waterproofed, of course) and used a long run of RS-232 
>>> cable plus power back to the digitizer board?  This is similar to what 
>>> Motorola or Synergy Systems sells in their Timing2000 product.
>>>
>>>
>>>> Date: Mon, 22 May 2006 11:16:49 -0800
>>>> To: psn-l@..............
>>>> From: apsn 
>>>> Subject: Extending coax on Motorola Oncore GPS antenna
>>>>
>>>> I need to move my GPS antenna (Oncore GPS for WinSDR timing) to a 
>>>> location such that I need to add 50' of coax.  What do you suggest 
>>>> for coax and where can I find adapters for that tiny right-angle MMCX 
>>>> connector?
>>>>
>>>> Thanks,
>>>>
>>>> Bob Hammond
>>>> Public Seismic Network - Alaska
>>>> http://apsn.awcable.com
>>>
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--
Jim Hannon
http://www.fmtcs.com/web/jmhannon/
42,11.90N,91,39.26W
WB0TXL
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