[time-nuts] Thunderbolt antenna
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).
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.
> 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?
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