Wednesday, May 26, 2010

What frequency standard?

I think the frequency readout of my IC-910H is out by about 400Hz and unfortunately I can't receive any accurately calibrated beacons like GB3VHF to set it with. I also like to check my K3's calibration from time to time and would like to take advantage of the option to lock it to a 10MHz frequency standard should Elecraft ever provide it as originally promised. So I decided to have a look on eBay for frequency standards.

There seem to be a number of ex-equipment 10MHz rubidium frequency standards at prices starting from around £50 - which is about the right level for me - available from China. For a bit more you can have a GPS locked time and frequency standard, though where time is concerned the NTP software is good enough for me. There is also a smart looking Quartzlock off-air frequency standard, though that is a bit outside my price bracket for this and would take up a bit too much space for the G4ILO shack.

I don't know anything about this equipment and aren't sure if any of these things would be any use to me. The rubidium frequency standard pictured has a frequency adjustment setting which surely defeats the object. If you need to calibrate it against something else then that's no use to me. I want something of known accuracy to calibrate my radios against. Perhaps the GPS type would be more useful?

Does anyone know about these things?


Theodore said...

Hmmm... Adjustable master frequency standard, there is a Zen conundrum if I ever saw one.
Lets add it to the sound of one hand clapping.

Justin said...

A GPS standard fits the bill perfectly. No need for adjustment, so turn it on, let it run for a day or so and its good to go. I just finished a weeks training course with Shomandl, they manufacture frequency standards and we purchase them for use in our equipment. Anyway, to calibrate they're lower standalone standards, they use a GPS disciplined standard. If its good enough for them, then surely its good enough for a couple of HAMs.

Maurice.G4DVM said...

Hi Julian,
It is OK to talk about getting a frequency standard, but how would you use it? Adjusting your rig to zero beat receiving the 10MHz output frequency is likely to achieve not much better than 10 Hz i.e, about 1 part per million. When you translate this accuracy to 70cms 430MHz this eaquates to 430HZ i.e. no better than you mentioned above.

A more useful addition to your shack would be a second hand ex-professional frequency counter with a high stability time base. A lot of these have an standard frequency output socket (usually at 10MHz) which you can use as a stadard for your other purposes, in addition to being able to measure the frequency of all your transmitter frequencies, inculding home brew QRP rigs Hi !

One of the Racal counters model 1991 upwards is a good one to look at. This will give you the facility of reading a 144MHz frequency to 10Hz, which is good enough I imagine! Have a look here.

Regards. Maurice.

g4ilo said...

Thanks for the comments. I thought that I could feed the 10MHz output into a circuit that would generate harmonics so that I could adjust my rigs at the highest frequency they can receive on e.g. K3 at 50MHz, IC910H at 440MHz. The trouble with equipment like that Racal frequency counter is that I have nowhere to keep something that big. And although it may have high stability it presumably still needs a frequency standard to be calibrated against.

Maurice.G4DVM said...

Hi Julian,
You must be really pushed for space!. The Racal 1991 is one of the smallest proffessional high accuracy frequency counters on the market. Front panel is 22cms x 9 cms. Front to back 32cms.

However, your view on calibration is just as valid for your 10MHz reference oscillator from China. How would you calibrate it?

The only way I can see you solving this problem (without spemding hundreds of pounds) is to home brew your own off air frequency standard locked on to the 60kHz MSF tranmitter located a few miles away from you in Cumbria. This would not involve buying anything from China and would not involve any recalibration whatsoever.

As I don't believe your blog supports uploading documents. I am sending you via email a two part PDF document, describing a DIY frequncy standard locked to the 60kHz transmitter. Hope you find it interesting.

73s Maurice G4DVM

Alex Hill said...

You might want to ask Kevin, M0KHZ as I vaguely remember him making a gps standard a while ago.