[TMC] GPR-92
Robert Nickels
ranickels at gmail.com
Wed Mar 24 21:50:38 EDT 2021
On 3/24/2021 3:30 PM, Richard Knoppow wrote:
> I also got the instructions for the TMC GPR-110 but it seems to have
> been designed for general purpose rather than maritime radio use.
> Again, I wonder if anyone has either set and, if you do, what your
> opinion of them is.
I may be the person John referred to as I do have a GPR-110 in
non-working order and from what I've been told, it may have never been
any different, at least not for long periods of time. It's the rack
mount cabinet like in the manual, not the rounded-corners desktop
version shown in the sales bulletin.
The initial upconversion is to 163.5 MHz, then to 3.2 MHz and finally to
250 kHz. The RF tuned circuits use varicap diodes for tracking which
sounds good in principle but I've found to be an additional source of
error in alignment. The 250 kHz output is also fed into a phase
comparator along with a reference signal to produce an error signal that
controls the frequency of the second LO. The manual (under)states: "a
number of loops are established that set and maintain the selected
frequency"...and therein lies the problem.
From what I've been told, several factors resulted in the GPR-110's
failure. It was a complex and intensive engineering undertaking, the
company was basically running on fumes at the time, and competitors
already had equivalent solutions on the market. As John says, there
were numerous difficulties with the small number that were put in the
field and the receiver may never have been fully debugged and reliable.
I figure I'll spend some time on it some rainy day, but other than to
prove it can be made to work in some fashion, the performance and
reliability would probably not be worth the effort.
73, Bob W9RAN
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