IC-M700TY

Yes, today it dropped in. The radio is in wonderful condition. I think, it has never seen any ship from the inside.

Polyakov I/Q-SDR update

Some success but some fall backs too. The regular reader will know, I was working on a subharmonic SDR design for a while, with decent breaks however.

The design involves a 5.0688MHz canned oscillator, two pairs of anti-parallel diodes and some audio amplification (TL082).
Theoretically there also is a front end with a J310, but, it is not working, God knows why... need to look into this... Not oscillation, no attenuation, no amplification, no nothing....

I/Q works, however, the correct phase-shift adjustment is not easy, three parameters to play with. The sideband suppression (image canceling) is surprisingly good, with the proper phase-shift.

Presently the fun is spoiled by a major 50Hz contribution, I've seen that before, proper tins required ;-)

QRX

need a break....

FRT-7700

This is stone-age stuff. But yeah, why not. Have been to a radio flea market today. With no further wishes on my list, it was some sort of gamble, the ride took me 1h30min each way, road construction, severe congestion, etc. The three hours in the car payed off however.

Presently the aerial of the Polyakov DC grabber receiver is matched by means of my QRP transmatch, which I actually do miss in my non-QRSS QRP work. Strolling along the lines of tables with used appliances, my attention was drawn to a table with communications receivers only. Not that I would be in need of any, really. However, there it was, a sole FRT-7700, shining into my face. The €40.- were payed without even attempting to negotiate.

Thus, soon-ish, the transmatch will again be wired up to something that also transmits and the QRSS spectrum receiver will have it's own dedicated antenna tuner. To be honest, not having it built myself makes me feel kinda odd. Could thus well be that the FRT will be replaced by something else; this something could well be a CLC-pi-filter, the classic.

30m QRSS-RX modification

Recently, I have seen some traces of lower sideband interference in my 30m-qrss receiver. Thus, the filter crystal went back in again. This time, with some experimentation and thinking. The crystal is now in series with a 22pF capacitor, pulling it just a little, such that the resonance is about the qrss band and a little bit above. Doing so, I hope to have removed contributions of the lower sideband.

22m Hifer RX (TX)

Super-heterodyne or not, that is the question. The 22m band is wide, that would not really encourage a superhet design with a crystal filter, at least not when all of the band is to be observed as a spectrum.

Thus, here come the crystal combinations (what did you think???):

• 6.5536 + 7.000 = 13.5536
• 6.5536 + 7.005 = 13.5586
• 6.5536 + 7.015 = 13.5686

Spot on, I would say. For a DC-RX, I would consider to slightly pull one of the crystal and mix. This would possibly enable to observe the full 22m range.

The superhet solution would probably point towards a 6.5536MHz IF, since those crystal are certainly cheaper.

The nice thing on this combi is, there is a ceramic resonator available (7.02MHz), which can easily be pulled in an oscillator circuit.

Source for the crystals and the resonator: box73.de

Yeah!

Yes, luck had it, I found an ICOM IC-M700TY and bought it :-))

The gear is perfect, really. It comprises the two maritime modes USB and F2B, but also A1A, A3E and LSB, which is unusual for maritime radios. This radio is intended for TOR (Teletype Over Radio).

As in all professional radios, there is no main dial (aka VFO-knob). The frequencies, RX and TX are independent, are selected numerically.

This is a no-nonsense professional radio, just like the one I was trained on for the General Operator's Certificate. The only difference here, no DSC. However, DSC could even be run externally, since the radio is prepared for TOR.