Sunday, 13 March 2011

Huff and Puff Stabilisers - they really DO work!

In an earlier post I alluded to the fact that I was building an X-lock by Cumbria Designs with a view to incorporating it into my 30-year-old Yaesu FT-107M as that particular radio has (or had) a bad case of "driftitis".

X-Lock is a software based derivation of the "Huff and Puff" oscillator stabilisation technique whereby the frequency of an oscillator is sampled, compared with a crystal or other high stability reference, sampled again and frequency nudged in the opposite direction to any detected drift.

A couple of sessions with the soldering iron saw the kit completed without any issues, and then followed quite a bit of "circuit-bashing" (study of schematics!) plus reading up of other implementations of X-lock into old equipment.   After all this I had on the back of an envelope a plan for interfacing the two pieces of equipment.

Last weekend I lashed up a test which looked promising, and finally, this weekend the project was completed and I now have an "X-locked FT-107M".

The X-lock fits very snugly into the radio, and all of my interconnections are such that no mechanical or electrical changes have been made, and it could all be removed without a trace, if required.

This will all be written up properly in due course and posted on my web site - here and now isn't the place for detailed explanations, but the following two "Argo" screen grabs illustrate just how effective the unit is on received signals.

They both show reception of the 14MHz beacon IW3ICH and were grabbed withing minutes of each other, one with X-lock controlling the frequency, and the other with just the bog-standard built-in circuitry in control.

The above trace is with X-lock disconnected, in other words how the "vanilla" FT-107M performs even after the radio has been powered for some considerable time.
Now look at the same signal with X-lock in charge :-
I would say that's quite an astonishing result and the screen grabs speak for themselves!

One of my long-term objectives has been to improve the frequency stabilityh performance, if possible of my old radio gear to the point where they could be used without any embarrassment on modern modes such as WSPR, and I would say that the X-locked FT-107M is now "good to go" on WSPR.  I just might try it today ...

1 comment:

  1. Try replacing the 2 x 100uF storage caps before the opamp with Tantalum capacitors. Reduces the self discharge (leakage) and saves the X-lock correcting all the time