[time-nuts] Homebuilt GPS receiver...
Burt I. Weiner
biwa at att.net
Mon Sep 22 12:28:01 EDT 2014
Back in the mid 70's I was involved in the home-brewing of a receiver
for our 2-Meter FM Ham repeater on Mt. Wilson. It was fairly
sophisticated with a double balanced mixer and all kinds of fancy
circuitry. The I.F chain consisted of 3 chips which were limiters
enclosed in separate machined metal boxes. The gain in the I.F. was
so high that it would tend to go into oscillation if you even looked
at it. The secret to making it unconditionally stable was to flip
the polarity at the output of the first I.F. going into the I.F.
transformer. Since the circuit described for the homebuilt GPS
receiver uses a balanced I.F. chain, I wonder if that's a part of how
he got it stable?
Quote from the description: The LMH7220 adds 59 dB of gain making a
total of 119 dB for the whole IF. Deploying so much gain at one
frequency was a risk. To minimise it, balanced circuitry over a solid
ground plane was used and screened twisted-pair carries the output to
the FPGA. The motivation was simplicity, avoiding a second
conversion. In practice, the circuit is stable, so the gamble paid-off.
>Subject: Re: [time-nuts] Homemade GPS Receiver
>Quite a project and extremely well presented and executed.
>Thanks for the link to a fascinating read!
>On September 17, 2014 5:34:38 PM CDT, Peter Putnam <ni6e at sbcglobal.net> wrote:
> >The link below describes a The LMH7220 adds 59 dB of gain making a
> total of 119 dB for the whole IF. Deploying so much gain at one
> frequency was a risk. To minimise it, balanced circuitry over a
> solid ground plane was used and screened twisted-pair carries the
> output to the FPGA. The motivation was simplicity, avoiding a
> second conversion. In practice, the circuit is stable, so the gamble paid-off.
> >It is presented in a detailed and elegant manner that is certain to
> >appeal to this reflector's subscribers.
Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California U.S.A.
biwa at att.net
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