[time-nuts] looking at creative ways to route GPS signals through a home to a Thunderbolt

[dave powis]

Hi Scott,

Looking at your proposed implementation below, you may like to look at one of my kit products - a distribution amplifier which will split a GPS antenna signal up to 4 ways, and will act as the power source for the antenna.  There is no need to disable the 5v feeds in the receivers, since there are blocking caps in the DA, although if you do have the software control of them, it would be better to disable!

Have a look at http://g4hup.com/DA/DA1_4.htm and look for the details of the G version.  Hope this may be useful to you.

Regards,
Dave, G4HUP

http://g4hup.com




________________________________
From: Scott Burris <slburris at gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Wednesday, 8 April, 2009 6:21:11 PM
Subject: Re: [time-nuts] looking at creative ways to route GPS signals through a home to a Thunderbolt

This is an unused coax run, so there's no AC or DC on this line to be a 
problem.
I do carry feeds from 4 security cameras via a 4 channel modulator on 
other coax
runs to elsewhere in the house, but I can't see trying to mix this 
application with GPS
to this room -- I should really just digitize the security cameras and 
put it on the IP network, a problem for another day.

I've got some vague thoughts about splitting the received signal in this 
room to go
to the Thunderbolt, an NTP server, and one of my homebrew GPS clocks 
(answering
phk's question about just pushing the T-bolt output through the coax from
the garage). My priority though is to get my T-bolt permanently 
installed and
running 24/7 so it can be my house frequency standard.  All the other 
uses are secondary to this.

In any case, it sounds like it's a worthwhile experiment.  I'll have to 
go through
my antenna collection and see what works best.

Scott

brooke at pacific.net wrote:
> Hi Scott
>
> Most GPS antennas have some amount of gain and that varies from none to
> over 50 dB, with about 20 to 30 dB the most common.  The idea is for the
> system noise figure to be established by the antenna and not the coax loss
> getting to the receiver.
>
> To have gain requires DC power to the antenna.  It turns out that most GPS
> antennas run fine on 3 to 5 Volts.  For example the Motorola Timing
> antenna (white inverted ice cream cone)is specified to run over that
> voltage range.
>
> So you're option C can work if you properly manage the RF and DC aspects. 
> If the DC aspects are not handled properly you risk smoking the antenna.
>
> One of the potential problems is there may already be DC or AC on the CATV
> coax that's not compatible with the GPS antenna DC requirements.  Do you
> have a diagram of the CATV system?
>
> Have Fun,
>
> Brooke Clarke
>
>  
>> I have a Thunderbolt (thanks TAPR!) located in a second floor room of my
>> house which
>> has only an obstructed view of the sky.  There's no easy way to get to
>> that room, short
>> of putting an antenna on the roof and punching a hole in the wall to get
>> inside.  For some reason,
>> my wife takes a dim view of that plan.
>>
>> Plan B would be to mount the antenna near an attic vent, run the cabling
>> inside, go through the
>> attic and drill down into one of the inner walls to terminate in an
>> outlet box of some sort.
>>
>> So the dedicated time-nuts may laugh at plan C.  This is to mount an
>> antenna on roof near the garage
>> and connect to the RG6 CATV run from the garage to this room.  I'd guess
>> it's about 60-70ft of RG6.
>> Can RG6 pass the 1.5Ghz signal successfully?  Is the Thunderbolt
>> sensitive enough to be used this way?
>> Has anyone tried this?
>>
>> Scott
>>
>>
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