Saturday, October 31, 2009


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.

Wednesday, October 28, 2009

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:

Monday, October 19, 2009


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.

Sunday, October 18, 2009

Slow Train Coming

Not much progress on the DRM-RX yet, besides me looking into the gate design of TTL and LS-TTL NANDs and NOTs. BTW, both are almost identical. I wonder if it would be better to use open-collector gates when using the logic-circuits in analog mode... Browsing the internet, I only found standard TTL gates used. But most designs, other than oscillators, are making essentially use of the logic functions. Hmmmm, looks like I will have to hack things into SPICE, before continue thought on matters.
As Bob sings, "there's a slow train coming".

Thursday, October 15, 2009

DRM RX considerations

Some ideas settled into a first design idea.

I'll be using inverters, such a 7404, maybe LS.
The oscillator will be a Pierce design.
The attempt will be to use as many gates of the inverter linearised.

As soon as there's more, I'll provide an update.

Wednesday, October 14, 2009

On today's menu: DRM

Stumbled across some stuff, making me think I'd need to design and build a DRM-receiver. First ideas evolved; the design will be using (pulled) crystals and logic ICs.

Frequencies the receiver should be receiving, standard crystal frequencies provided:
  • 3995 kHz (BBC/DW) - 4.000 MHz
  • 6130 kHz (BBC/DW) - 6.144 MHz
Other frequencies be reached by standard crystals:
  • 3965 kHz (RFI) - 3.9321 MHz
  • 5995 kHz (Radio Australia) - 6.000 MHz
  • 6015 kHz (TDPradio) - 6.000 MHz
  • 9850 kHz (Radio Prague) - 9.8304 MHz
  • 11995 kHz (RDP Int.) - 12.000 MHz
For the fun of it, frequencies reached by standard crystal frequencies divided by two:
  • 1008 kHz (Economic. Ch.) - 2.048 MHz
  • 1548 kHz (DW) - 3.0721 MHz
The plan, for now, is to build something for the first list provided in this post.

Saturday, October 10, 2009

FT-450 update

Had a little time to play with the radio. Actually, compared it to the IC-703, which is equipped with DSP too.

The FT-450 is able to digg out signals the IC-703 is not able to bring up. This caught me by surprise, sort of.

40m / 20m two band MEPT

  • MEPT for 14.000800MHz
  • QRP crystal for 15m (21.060MHz)
  • => 21.060 - 14.000800 = 7.05992
  • inverts! 

Thursday, October 8, 2009

I could not resist... a sneak preview

That was me not posting, since I had my nose in the books, well, and wikipedia ;-)

The exam is written, new books did not arrive yet, no parties or other obligations... a perfect time to ... buy a new rig.
Which I did!
Now, there is an additional small big one sitting on my shelf. Small and big to the same time? Yep, I bought a Yaesu FT-450. Primarily w/o the internal tuner option. The very friendly dealer gave me the hint, that in fact buying the tuner-less FT-450 and the tuner ATU-450 itself later on will actually be saving money over buying the FT-450AT. We both agreed that this does not make any deeper sense, marketing-wise and could be explained by a stragetic error in Yaesu's HQ only.

Experience sofar, nice rig, however pretty useless without a manual! I guess, I will have to free space in the shack to allow easy access to the printed documentation. Some settings come along easy, for some settings one needs to dive deep into the menus. At a first glance, the rig seemed to be factory set to voice operators. Actually, I was even dissapointed with the CW capabilities at first. However, with the help of the manual, I am coming closer to settings which would satisfy my needs for comfortable A1A operations.

Things I liked directly:
  • the key/paddle connects to the front face
  • 3.5mm key- and phones-connectors
  • nicely arranged display
  • all dials positioned low
  • flat "car type" fuses
  • receives well below 100kHz (tested on DCF77)
Things I disliked directly:
  • noise from the AF stage, even w/ volume set to minimum
  • ATT on by default at lower frequencies
  • single leads power-cord (not twin-lead!)
  • tiny GND-connection screw
  • a lot of the default settings
A few words to the last point. The main dial, you would assume, dials in all modes. But no, the default setting of the main dial is not to do anything when in AM or FM modes. To me, that does make little sense. In the default settings, the only way of navigating around the SW-BC ranges in AM is the smaller "select" dial, which defaults to 5kHz steps. At short-wave ranges, this does make some sense, however, it does not, when going lower, since in Europe, tuning steps for MW-BC are required to be 9kHz wide... Since the main menu is silent about the main dial, in order to activate the main dial for AM and FM, one has to activate the extended menu first.
Settings settings settings...

Thus, more on the radio, as soon as I understood more of the transceiver's main, extended and hidden menues.