[time-nuts] A few questions about Tboltmon

Chris Waldrup kd4pbj at gmail.com
Thu Aug 13 21:57:13 EDT 2015

Thanks everyone. In addition to the blown transistor that feeds 5V down the coax, the one week out of box Motorola hockey puck antenna was blown too. I bought it in 2006 as a spare and I broke the shrink wrap two weeks ago. 

So I will order another spare but see if I can fix this spare. 

It's definitely worth it to have a few extras!!!


Sent from Mailbox

On Thu, Aug 13, 2015 at 8:01 PM, Magnus Danielson
<magnus at rubidium.dyndns.org> wrote:

> Hi,
> On 08/08/2015 07:05 PM, Bob Camp wrote:
>> Hi
>> A factory reset will not brick the unit.
>> Either:
>> 1) Your TBolt is blown
>> 2) The cable has an issue
>> 3) The antenna has an issue.
> I've seen them all over the years, so neither is necessarily the most 
> likely. I'd also add:
> 4) Power-issue
> 5) Serial cable problem
> For this case 1-3 should be your culprit.
> Oh, do remember that engineers invent the most complex scenarios of what 
> the failure mode is, but fail to identify the simple ones such as power, 
> cables and connectors failing.
>> For troubleshooting this sort of thing, multiples of each are a
>> handy thing to have. Baring that:
>> 0) Put a DVM on the coax and see if you have bias to the antenna
>> 1)  Hook up a TDR to the cable and ring it out both with a load and a short on the end.
>> 2) Put the antenna on a *very good* spectrum analyzer and look at what is coming out.
>> 3) Grab a signal generator that will simulate a GPS constellation and drive the TBolt with that.
>> Since nobody (other than Magnus) ever has the sort of gear for 1-3, and it’s all pricey stuff
> TDR is a nifty tool for this sort of thing so 1) is nice, but it won't 
> really help you and you will have to know what to expect from a 
> unpowered LNA. Spectrum analyzer will not directly help you since the 
> satellite signal spectrum is below the noise-floor, but you *might* see 
> the amplified noise as shaped by the LNA pre-filtering, which is 
> hopefully SAW filtered, so 2 is doable but tricky to interpret for the 
> novice. If you have a constellation simulator lying around, it will help 
> you to see if the receiver is working at all, but even I don't have that...
> Having a VNA helps, and the nifty TinyVNA for instance will be quite 
> useful. Similar to the TDR, it sends a signal up the wire and analyze 
> the response, but in frequency plane rather than time-plane. Again, some 
> experience is required but this is a good time to learn.
>> the simple answer is:
>> 1) The antenna is probably the cheapest part of the setup. I’d swap it out first.
>> 2) The cable is cheap but a pain to run, is it #2 or #3.
>> 3) Hook up another timing receiver to the cable. There are lots of them out there in the $100 to $150 range.
>> TBolts do die. My experience is that roughly 1 or 2 in 50 show up with a fatal issue. Another 1 or 2 show up
>> with a (correctable) minor problem. I have had one drop dead after running for a while.
> I would grab an antenna, toss it out a window and see if I get anything. 
> It is always handy to have additional antennas and cables around, and 
> for checking things to be operational, only modest requirements in type 
> and position is needed.
> Similarly, having another GPS receiver to see if I get any form of 
> signal is a great tool.
> Just taking the time to do quick and dirty tests helps. I've found that 
> I made stupid mistakes, so just doing a round of quick reality checks 
> have been important hints to find errors.
> Cheers,
> Magnus
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