Thursday, August 27, 2009

What frequency am I on?

As i spend more time in the microwave region, frequency stability becomes much more of a problem for me. While out in the field I need to be able to point my dish with roughly 2-4 degrees of horizontal/vertical accuracy, then be on the right frequency to make a QSO with the other station. If any of these variables are off I can potentially miss the contact and lose points. With the use of a computer program I can predict the azimuth of the Sun, point my dish at it, then be able to calculate my heading with use of a centerline. Now I only need to worry about frequency.

Currently my method of determining my frequency is to listen for a radio beacon. Around New England there are two regular beacons on 10GHz that I use; the Mt. Greylock beacon and the WA1VVH beacon. One problem is that the WA1VVH beacon is often down during the contest because Harry (WA1VVH) is home operating on the same antenna. Another issue can arise when you don't have a clear shot to the beacon location. This past contest weekend, on Sunday, I had the pleasure of operating with Mike, N1JEZ, who has a portable GPS stablized 10GHz source with him. It doesn't matter where you are, as long as you can lock to the GPS system you can produce a carrier at exactly 10,368.000MHz. My transverter drifts fairly heavily, upwards of 20-30KHz. Having that source was a lifesaver, I simply tuned around .000, calculated my offset, changed back to the frequency we agreed to meet on, then added back in my offset, voila!

My new problem: I'm not going to be operating with Mike, N1JEZ, next contest weekend.

I've been reading about the new DEMI/N5AC Apollo A32 synthesizer board lately, it is being touted as a replacement for the DEMI Microlo (Which is the source of my drifting problem). The only downside to the A32 is it's less than great phase noise, but is bad enough to really worry about? I took the plunge and ordered one. I'm not planning on installing it right away, I may actually just play around with it for a while and see what other folks find with it in terms of performance degredation. Then I had a great Idea, I could use it along with my 10MHz GPSDO to create a 10GHz portable marker! No more guessing at what my frequency is?

Then I realized that DEMI beat me to it and put together the A32 with a nice enclosure with a knob that has several presets. Check it out here! Again, I took the plunge and ordered one. I can envision using this for a number of projects, including using it to test my S-band down-converters from 2401 to 144MHz. It could really come in handy.

Now, both the A32 and WSSA require 10MHz external reference. I had built a GPS disciplined 10MHz oscilator based on the N1JEZ/W1GHZ/G3RUH board, so that was a good start. I also picked up a Thunderbolt GPSDO from Ebay, but it's been sitting on the shelf unused. Tonight I finally assembled the power cable for the Thunderbolt and managed to get it up and running, here is a pic of the unit and power supply.

With any luck, I should now have mostly solved my frequency accuracy issue, I'll always be able to calculate my offset from the marker. If the results come back positive for the direct Microlo replacement, I'll think about changing it out. The issue with going that route means that i have to have 10MHz with my rig, or run a cable from the Car. That isn't always convenient.....

Now, if DEMI ships my order within the week I'll be ready to go for the second weekend of the contest!

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