[sdiy] A Frequency Standard for Poor People?

[Magnus Danielson]

From: Glen <mclilith at charter.net>
Subject: [sdiy] A Frequency Standard for Poor People?
Date: Mon, 15 Dec 2003 08:32:17 -0500
Message-ID: <4.1.20031215081602.009582f0 at mail.charter.net>

Dear Glen,

> In the past, I've seen DIY articles about building inexpensive, precision
> frequency references. Unfortunately, I don't have any of these articles
> handy at the moment. In concept, I think they all relied on extracting
> precision reference signals from "someone else's" existing reference signal. 
> 
> Such as, extracting a reference signal from:
> 
> "time and frequency" SW radio stations

In the US/North America you can sniff up a load of usefull signals from NIST.
There are many different projects for it. Further, you can sniff the LORAN-C
chains and there is a there is a full-featured project for that from Dave
Mills. Beyond that there is the Rugby 60 kHz and DCF77 at 77.5 kHz here in
Europe in addition to the LORAN-C chains.

> signals derived from color television broadcasts

Can be tricky if you are not sure about the traceability of the signal, i.e.
if you know that it actually derives from a stable enought source. Both PAL
and NTSC allow for single digit PPM deviations and speed of deviations can be
quite severe.

> GPS receivers

I am not sure that I've seen a good project for it, but have considered doing
one myself.

> Anything else?
> 
> Does anyone on the list know about any of these methods?

Yes. ;O)

> I could really use a reliable frequency reference, to check the calibration
> of a frequency counter. I want something that is very accurate, but also very
> cheap. Is it possible?

Define cheap.

> Which method gives the best results, and which is the least expensive system
> to construct? Unfortunately, I can't afford to spend much money.

My bet would be a GPS receiver. Many if not all have PPS outputs. You then use
a VCXO and lock this to the PPS through a suitable PLL/FLL method. The details
of this locking determines the accuracy and ability to trace the frequency, but
you can get *really* good results with it, but a fairly quick and dirty
solution should be sufficiently good for most amateur uses anyway.

I've made a rought estimate of about 300-350 USD for such a receiver (including
antenna). That included a rather good VCXO (about as much money as the GPS
receiver module itself).

Cheers,
Magnus