Tuesday, August 31, 2010

MF/LF Dual Band SDR

Just an idea, what about a 2.000MHz local oscillator. For regular SDR purposes, this will and up at 500kHz centre frequency. Ok... not that surprising.
What about taking this 500kHz signal and use it as LO for another SDR setup. Well, that would provide as with a centre frequency of 125kHz.

Assuming a regular 48kH sampling, two interesting frequencies are in reach:
  • MF: 476-524kHz
  • LF: 101-149kHz

Wednesday, August 18, 2010

H-Probe (the Aerial Formerly Known As Shielded Loop)

Short update, not only the name changed, some more happend.
Parts are collected, the TL592 based amplifier should be done in minutes.
The shielded loop is past now, I will reorganise the inside of the tuning-box. The toroid is removed, coupling will be done at the high impedance region of the loop, i.e. at the tuning capacitor.

Oh, should you wonder about the new name, this contraption is near to entirely screened, any E-field should therefore essentially be excluded from detection. A magnetic field, or H-field, will induce a current in the loop. This current will peak at the resonance frequency, creating a high impedance RF signal across the tuning capacitor. The aerial therefore probes the H-field, hence the new name.

Tuesday, August 17, 2010

Multiband QRP TRX

Just an idea, which pop up when I replied to G4CWX and had a chat with PA9QV. The question was, what to use as a low power travel CW setup.
And this is the idea: a couple of RockMites in a box.
All transceivers could share the connector, i.e. antenna socket, control button, key. Band select, in my plan, would be a rotary switch powering up an individual transceiver PCB.
As said, just an idea....
And... I still got the RockMite kits for 20, 30 and 40m waiting for solder... the 80m version could be brought from QRSS to QRP... the 4-band-QRP-TRX would be completed.

Shielded Loop (some photographs)

No new development yet. Here are some photographs to help the imagination. The loops will be provided with some amplifiers soon-ish.

There seems to be a rule of thumb for the dimensions:
Loop Diameters [cm] = Wavelength [m]

(e.g. 30cm loop diameter for a 10MHz loop)  :-))

For more information on materials and dimensions, please use the label "shielded" down below.

The loops for 30m and 40m.
The gap in the shield, opposite the capacitor.
The capacitor and coupling "box".

Sunday, August 8, 2010

Digital Flashback

Lately I was digging a bit in my goodies boxes... and some treasures surfaced in the for of digi-mode controllers.

Next to two TNC2s, a Kantronics KAM (w/ Pactor I), an SCS PTCplus, an AEA PK-900 and an SCS PTC-IIe found their way out of the dark.

Hmmm, this has been my active Packet-Radio and Pactor period. Now:
  • What happened to the controllers?
  • Are still in a working order?
  • Would they be able to communicate with modern computers?
  • Is there still software available, for these controller, which runs on modern computers?
  • Is there still activity?
  • What could the stuff be used for?
Questions questions....

I tested all controllers but the PK-900, which simply is too clunky for the tiny test space I freed.
The tests concerned the compatibility of modern computer hardware with those old controller, hence no radios connected, no RF generated.
So, here's some of the results and thoughts.

All tested controllers still worked.

For testing, I used three relatively new computers in the setup, running different operating systems: an Acer REVO w/ Windows Vista, an Acer Aspire One running jolicloud 1.0 and an MSI Wind under Windows XP. None of these computers have RS232-ports, which in modern times seems the first hurdle.
In a recent order, I purchased a cheap no-name USB-to-serial adapter (Prolific PL2303 chipset), which plugged into the SCS PTCs directly. For the other controllers, a "9to25"-adapter was required.
BTW, Vista provided me with the most struggle, a lot of blue screens, core dumps and what not...
jolicloud was the only real plug&play what the PL2303 is concerned, and smoothly installed the device as /dev/ttyUSB0.

Struggles aside, let's have a look at the results.


Software: PAXON under Windows Vista
TNC2 (TF2.6, modified to 10MHz Z80, 38400bps): doing just fine!
Symek TNC2S (TF2.7): something caused the TNC to stall in TX (remember, no radio connected!), with my hand placed on the controller, this did not occur. Seems there is some grounding problem between the PC, the USB-device, the TNC and the TNC's (linear) PSU.

AMTOR & Pactor

Windows software: Airmail3 for hams, Alpha 3.2, Simple32

Airmail3 seems to be the reference, it could talk to all modems, on either Windows flavors, although, it has been a struggle to have it talking to the KAM under Vista, no problem with XP though. Airmail3, as the name suggests, is an HF email program, which makes use of the WINLINK2000 Global Radio Email System. Airmail3 is therefore mainly programmed for handshaking with the servers of said system and therefore is essentially limited to Pactor.

Alpha 3.2 did only talk to the SCS PTCs, however, it did it well.

Simple32 simply did not work on Vista, whatever I tried (run it under admin, etc.). I got the main screen just once after hitting ignore on all error-messages, and, it did not at all look simple, hence I decided to not (yet) give it a try on XP.

Linux software: Kptc, minicom

Kptc flawlessly installed on my jolicloud 1.0 netbook. The program works perfectly with the SCS PTCs.

minicom seems the only easy way to communicate to the KAM. A software called Kamplus was written some years ago. I will try to compile it on my machine, I will post any success story; I will however spare you stories about failed software porting efforts.


Packet-Radio seems a dying mode, at least here in my region. When I moved here, I was eager to keep contact with my friends via the PR-network, I soon learned, that this region is not connected to anything. I wonder I that changed. Maybe APRS would be an option.

AMTOR was a very advanced technique, to the time when I got on the air for the first time. Those chirps were everywhere.... I have not heard many on the ham-bands lately. However, there seems to be one BBS station in Germany, DA5TOR, still on-air. I should give it a try, once my NVIS antenna is set up.

Pactor = eMail nowadays... DXers are busy using narrowband modes like PSK31. Pactor, when I did it last, could provide an even better robustness, but, for what price? Modern PTCs are more expensive than decent HF transceivers! No wonder that the mode more and more drifted towards professional application, e.g. marine communications such as SailMail.

Next Steps

Yes, I will take next steps. Among my transceivers, I will find the ones that make the least noise and provide the fastest switching.
A good start in this respect could be the Ten Tec Scout, if the frequency stability proves to be sufficient. I used this transceiver with PSK31 and Pactor I before, back in the days. The Scout is, besides the strange noise created by the PTO, totally silent, no relays involved... could be perfect.
Then there would be the Kenwood TS-140, which I used for WSPR for some weeks a year ago. The TS-140 has got relays, and is therefore somewhat unpleasant when used with ARQ.
Technically, the best fit would be the ICOM IC-M710. Not only was it built for the purpose, remember TOR (Teleprinting Over Radio) is a marine application, Airmail3 can actually control the radio via the NMEA bus. The IC-M710 also provides a frequency stability superior to most ham-radios. The radio however employs a lot of mechanical switching.
Last but not least, the following approach could be considered (this will be a new blog entry, when taken seriously): Use a DDS, controlled by a PIC, PICAXE or Atmel, as a LO for something that either already transceives silently, e.g. an old Scout, SmallWonderLabs PSK-series, N3ZI's 612-PCBs (see earlier blog entry) or this.

Sunday, August 1, 2010

Grabber up

The grabber is back online for some hours now. No adverse effects yet. Let's hope it stays that way.
There is one minor change, the grabber is now using my G5RV-jr and not the DCTL.