Analyser wrote:With regards to frequency accuracy, I've toyed with the idea of using a GPS-based frequency standard which is then buffered and split to drive a few instruments. A lot have an external 10MHz reference input at the back so they could all be driven from the same high-accuracy source. The only reason I haven't got round to it yet is that most of the stuff I use every day has a OCXO in it and 3-4 pieces of equipment all agree to within 1-2Hz after warming up.

There's a fabulously accurate frequency source that you're certain to be able to receive at your place - Radio 4 198kHz. It's referenced against the National Physical Laboratory atomic standard and is accurate to about 17 places after the decimal point! I run a 10 MHz frequency source, phase-locked to the 198 kHz signal. 198kHz is a bit of a pain to decode (it carries digital subcarriers with time data on them), but with a bit of cheap CMOS, you can get some great results.

Elektor, Practical Wireless and EPE all did a frequency standard locked to Droitwich. Beware if you come across the Elektor one - it was originally designed for the old 200KHz Droitwich frequency, they did an update when they changed to 198KHz.

What a truly ugly design! They've translated the 198kHz up to 9.9MHz, then back down to 100kHz. They then use a second PLL chip to get something close to a 50% M:S ratio. Why not run the first PLL at 20 MHz, phase-locked to the 198 kHz? If would then be trivial to use simple binary divider ICs (74HCT4040 would be a good choice) to give a range of useful frequencies, including the essential 10MHz used as a reference by most bench test gear!

I use something similar to their 198kHz receiver circuit, and (coincidentally) use a 4007UBE as the amplifier. That then feeds one of the gates in a 4093 to give good, sharp-edged squarewaves.

Another version of my phase-locked source gives a 9kHz output which is used as the reference for medium wave transmitters. In this instance, the 198kHz has a good active lowpass filter to prevent the medium wave signal breaking into the 198kHz receiver. On one RSL, I had the OFCOM clown claim that the transmitter was off channel. I proved to him that his frequency counter was way out of calibration!

I weighed up the costs of the phase-locked source against a crystal reference in an oven (a vastly inferior solution in terms of accuracy and stability). I found that the 198kHz off-air reference method is actually cheaper than a crystal in an oven! The only expensive component in the off-air reference is the ferrite rod aerial and the watertight plastic box to house it in! Everything else costs pennies.

Albert H wrote:

Analyser wrote:With regards to frequency accuracy, I've toyed with the idea of using a GPS-based frequency standard which is then buffered and split to drive a few instruments. A lot have an external 10MHz reference input at the back so they could all be driven from the same high-accuracy source. The only reason I haven't got round to it yet is that most of the stuff I use every day has a OCXO in it and 3-4 pieces of equipment all agree to within 1-2Hz after warming up.

There's a fabulously accurate frequency source that you're certain to be able to receive at your place - Radio 4 198kHz. It's referenced against the National Physical Laboratory atomic standard and is accurate to about 17 places after the decimal point! I run a 10 MHz frequency source, phase-locked to the 198 kHz signal. 198kHz is a bit of a pain to decode (it carries digital subcarriers with time data on them), but with a bit of cheap CMOS, you can get some great results.

I think they used to use the signal to control electricity meters as well?

Edit, just found this:

https://en.m.wikipedia.org/wiki/Radio_teleswitch

http://admin.mb21.co.uk/tx/userimages/15222orig.jpg

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'Some of the gear is away at a calibration house at the moment, but £180 later, I've got gear easily good enough to satisfy the OFCOM clowns when they want frequency accuracy, harmonic content, power output, conducted RF spill and all the rest'

Is this implying OFCOM do leave people alone if they 'follow the rules'?

Not really. It's just that sometimes I provide gear for RSLs and other licenced broadcasts, and the performance of the gear has to be stellar - the buggers love to criticise!

Is our guy on drugs? I don't think you can even get a pizza delivery in 20 minutes!

I've got to admit they rigol dsa 815 is pretty useful .my mate has one. you can plug in a rigol vb1020 bridge vswr, then connect any antenna to gets its frequency and db loss etc .it's pretty awesome .