[time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

David Fav frm04 at magma.ca
Thu Apr 21 20:05:10 UTC 2016


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  For long distance you need the right cable. Since the Antenna is
likely designed for 50 ohms use 50 ohm cable

	If it's a fixed installation maybe RG8 with pl259 to N adaptor would
be a good bet ?

	This garden hose cable might be cheaper than  RG6 quad.
 http://www.novatel.com/assets/Documents/Bulletins/apn032.pdf [1]
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 On Thu 21/04/16  6:48 AM , Bob Camp kb8tq at n1k.org sent:
 Hi 
 Most of the data sheets on RG-6 Quad show it around 9 db per 100’.
Like any of the  
 “old” (RG) specs, there really is no control on who does what
with a given type of 
 cable. The direct burial versions seem to be a little more
consistent.  
 Bob 
 > On Apr 20, 2016, at 6:48 PM, Pete Stephenson  wrote: 
 >  
 > On Wed, Apr 20, 2016 at 10:41 PM, Ryan Stasel  wrote: 
 >> All, 
 >>  
 >> I’m going to be installing a “permanent” antenna at home,
and will need a run of about 100ft to get from my workstation, to the
mast I’ll be mounting the antenna on (Symmetricom 58532A). I’ve
seen some indication that both the antenna and the Trimble
Thunderbolt won’t have any issues with running over 75ohm cable,
but thought I’d ask the “experts” whether I’d be better off
with some RG6 Quad-shield, or LMR400 (I’ve got a local source that
doesn’t know what LMR400 is, or what it’s worth)? 
 >>  
 >> Obviously I’d prefer to run and crimp RG6, but if I’d be
better off with LMR400, I’d rather run that now than go back into
the crawlspace again. =) 
 >  
 > I'm hardly an expert, but according to the Times Microwave
calculator 
 > at , [4] RG6 (of unspecified 
 > type, presumably double not quad-shielded) at 1542MHz will have a
loss 
 > of 12dB over a 100ft length. LMR400 will have a loss of 5.2dB over

 > that same length. 
 >  
 > The datasheet for your specific cable should show the loss
figures. 
 >  
 > The 58532A has an amplifier with a gain of >30dB, so it should
work 
 > well even at moderate cable lengths. 
 >  
 > Keep in mind that the Thunderbolt Starter kit came with a Trimble 
 > Bullet antenna (similar gain to the 58532A) and 75 feet of RG6;
it'll 
 > almost certainly work fine with 100ft of cable: the manual for the

 > Thunderbolt recommends RG-59 cable (presumably because it's cheap
and 
 > common) and states "The maximum practical cable run is just over
100 
 > feet." A graph in the manual shows RG-59 losing 15dB over 100ft, 
 >  
 > To be safe, you could always test it by connecting the 100ft of
cable 
 > to the antenna and putting it outside in a more convenient
location 
 > that has a similar view as your mast and seeing how the
Thunderbolt 
 > likes it. 
 >  
 > Also, keep in mind that the 58516A splitter can have between +3
and -3 
 > dB of gain depending on your luck as to how it was made. The
manual 
 > says that for relatively lossy RG-213 cable and the worst case 
 > performance of the 58516A, you should be fine with up to 174 feet
of 
 > cable with no line amplifier. 
 >  
 >> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A
at/near the T-bolt so I can experiment with other GPS(DO)s as well
(especially one of the JRMiller boards I bought and built (but never
finished) ages ago). Which brings the question, will the T-bolt
provide the oomph needed to power that splitter and the antenna over
that length of cable? 
 >  
 > Short answer: Yes. 
 >  
 > Longer answer: The Thunderbolt manual says it can supply 5V at up
to 
 > 45mA. The 58532A antenna draws a max of 27mA (with 20mA being 
 > typical). The 58516A splitter manual draws it uses 10mA. Worst
case 
 > usage is 37mA, which is within the limits for the Thunderbolt. 
 >  
 > Considering both conductors, 100ft of LMR400 has a DC resistance
of 
 > 0.304 ohms, so the voltage drop would only be 0.01V over that
length. 
 > That's well within specs for the antenna (5V +/- 0.5V) and the 
 > splitter (4.5 to 30V). 
 >  
 > The specs for Belden 1189AP quad-shield RG6/U cable with a
copper-clad 
 > steel center conductor and aluminum braid lists the total
resistance 
 > for both conductors to be 3.28 ohms over 100 feet. That's a
worst-case 
 > voltage drop of 0.12V over that distance, again within spec for
both 
 > devices. 
 >  
 > In short, LMR400 would be a better choice in terms of both signal 
 > attenuation and DC resistance, but the difference is more or less 
 > academic and either cable should work fine. 
 >  
 > Cheers! 
 > -Pete 
 >  
 > --  
 > Pete Stephenson 
 > _______________________________________________ 
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Links:
------
[1] http://www.novatel.com/assets/Documents/Bulletins/apn032.pdf
[2] mailto:pete at heypete.com
[3] mailto:rstasel at uoregon.edu
[4] http://www.timesmicrowave.com/calculator/>,
[5] mailto:time-nuts at febo.com
[6] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[7] mailto:time-nuts at febo.com
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