[time-nuts] Thunderbolt antenna

Peter Gottlieb nerd at verizon.net
Sun Mar 10 12:04:26 EDT 2013


The seller had a "make offer" so I tried $20 and it was set to auto accept.  I 
figure for $25 (with shipping) it's worth a shot for a new unit.  The Trimble 
data sheet says it is good for up to 75 feet of coax, I think I'll end up with 
about 50 here.  The antenna I have been using is a no-name pole mount unit with 
25 feet of attached RG-59 coax that came with the TBolt "kit" I initially got.  
I'm not a big fan of RG-59.

So what coax should I use?  Many people say use good RG-6, although the Dranetz 
power line units with GPS come with a 100 foot piece of 1/4" Heliax, I have to 
imagine that would be better.  Here's some on epay: 360492678643, but with wrong 
connectors.  Expensive, though, here are approx attenuation numbers at the 
frequency of interest:

RG-59        10.4 dB/100 ft
RG-6            8.4 dB/100 ft
Heliax          7.4 dB/100 ft         FSJ1-50A
RG-11          5.7 dB/100 ft

(Yes, I'm aware of the impedance differences)

It seems, just go with quad shield RG-6 and be done with it.  I even have part 
of a spool of that laying around.  Maybe more of an issue is how do you properly 
connect a TNC to that stuff (the antenna has a TNC).

Peter



On 3/10/2013 11:01 AM, Volker Esper wrote:
>
> Hi Peter,
>
> Why not. The antenna is optimized for that purpose (receiving GPS L1), 
> omnidirectional and tuned to the GPS frequency, snow skids down, birds can't 
> land on it. As N0UU affirms, there's nothing further sensational inside.
>
> I don't know, how proficient you are with radio frequency stuff, but a gain of 
> 35dB does not guarantee a good reception. You primarily need gain to 
> compensate (cable) losses. The noise figure (NF), for example, can get much 
> more important.
>
> What antenna do you use at the time? If you are using a magnetic car roof 
> antenna a Trimble Bullet surely will be a better choice...
>
> There are lots of GPS antennas on ebay for even less than 30 Dollars. I run 
> four different antennas, which I purchased from ebay and none of them has 
> failed so far.
>
> Volker
>
>
>
>
>
>
> Am 10.03.2013 06:07, schrieb Peter Gottlieb:
>> I'd like to get a better antenna for my Thunderbolt.
>>
>> I see Trimble bullet antennas type 57860-00 on ebay for $30 or so, specs look 
>> to be 5 volt 35 dB gain.
>>
>> Would something like this be a good choice?
>>
>> Peter
>>
>>
>>
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