[App_rpt-users] GPSDO comparison

Tom Hayward tom at tomh.us
Mon Aug 3 14:29:46 EDT 2015

Since asking about transmitter steering, I've been looking into the
feasibility of simulcast. The marginal difference between transmitter
steering and simulcast (in terms of equipment) is a GPSDO and a
transmitter that accepts a 10 MHz reference input. I have some leads
on transmitters--Quantars or some Daniels MT-4D. Other transmitter
recommendations are welcome, but what I'm really curious about is the

It looks like the Trimble Thunderbolt is the gold standard.

At less than half the going price of Thunderbolt, you can find these

Some are labeled Trimble and Huawei, so I think it's safe to say they
are neither. The question is: are they any good? It looks like KE5FX
has done some testing:

I don't really know what to look for in the graphs, but he says in his
conclusion "the BG7TBL unit is actually running at about 9.999 999 999
800 Hz". Is this a deal-breaker for simulcast? If all transmitters
have a BG7TBL GPSDO, does it matter that they aren't exactly 10 MHz?
Is anyone running these GPSDOs with RTCM simulcast that can comment on
their performance?


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