600m SDR RX (TX)

As we know, presently there are a couple of frequencies of the 600m band open to amateur radio operators.
Most of authorities allow transmission somewhere above 500kHz. In The Netherlands the permitted range is 501-505kHz. In the future, depending on the decision of the WRC12, this will possibly change to 472 to 480kHz. The U.S.of A. proposed the following ranges 461-469 and 471-478 kHz.

Lets look at the (inexpensive) option the box73 SDR. The 80m version of this receiver uses a 14.000MHz oscillator. Operation on the 600m band can be achieved by changing the front-end filter and the SDR-LO.
Considering 48kbps sampling, the LO-frequencies would be the following

• QRG: 470kHz - LO: 1.843MHz
• QRG: 500kHz - LO: 2.000MHz

This will result is RX-ranges of:

• 460.8 -/+ 24 = 436.8 .. 484.8
• 500.0 -/+ 24 = 476.0 .. 524.0

Concluding, a decent 600m receiver can be built with LOs using regular canned oscillators.

600m with CB-XTALs follow up

Hi there... I am back!
Presently, amateurs in The Netherlands are really happy, not only have we got the permission to transmit on 4m, we also may transmit on 600m again. For the time being between 501 and 505kHz.
For this range (well, to the upper QRG of 504kHz) this article could lead to a cheap signal source.

However, in about a month's time, we will know is we need to redesign our exciters, i.e. to the range 472 to 480kHz. So, lets have another look at the cheap crystal solution.
The new range is not that easy really. One solution would be the mixing of two standard xtal frequencies:

• 4915.2 - 4433.6 = 481.6 somewhat high, could be pulled into the range

A spot on solution would be a 10m QRP crystal (28.060MHz) on its fundamental mixed with a 9.8304MHz standard crystal:

• 9830.4 - 28060/3 = 9830.4 - 9353.3 = 477.1

Another spot on option: a 40m QRP crystal, mixed with a 6.5536MHz standard xtal.

• 7030 - 6553.6 = 476.4

Starting from lower frequencies, crystals from box73.de:

• 14745.6 - 14270 = 475.6
• 7025 - 6553.6 = 471.4 (pull!)
• 3550 - 3072 = 478
• 4000 - 3530 = 470 (pull!) (*)
• 3555 - 3072 = 483 (pull!)

Subractive mixing has the advantage that some thermal effects may cancel. Assume to us several standard crystals in a super-VXO.
Mind you, the higher the frequencies, the easier to pull, i.e. create a nice tuning range. However, lower frequencies will give better stability.

(*) Note, there is a 4.00MHz ceramic resonator, which will allows for a nice VFO. Use a Pierce oscillator to obtain a QRG above the ceramic resonator's series resonance.