Thursday, April 28, 2011

Super Radio SS-301

Yesterday I got a notification to pick up a parcel at the local supermarket. Yes, supermarket, the post office was closed and "out sourced" to my local grocery. Actually, this even has an advantage to me, opening hours are much more convenient.

So, today it was pickup time for a parcel from Thailand. In the parcel, a "Super Radio SS-301" handheld transceiver. You may not have heard about this brand nor the model... it is a clone of the Albrecht AE2990AFS, aka Magnum 1012, aka Dragon SS301. Imagine, the radio incl. shipping set me back not even €170.- (check ebay for the present conditions).

A guide for frequency coverage modification was provided inside the box. However, other than this single sheet of paper, the radio, a battery case, and wrist strap and a rubber duck aerial, the box did not contain anything in addition. I guess, I will have to hunt down a manual on the internet (probably not the most difficult task ever).

The actual modification itself, from whatever mode to 12m/10m operation, was done in not time at all. Contrary to the guide, two solder bridges had to be removed (Soder Wick) first. Temporary shorten terminals 1 and 2 whilst switching on the radio is a bit tricky, not difficult however. Having selected the correct code, for hams "0" would be ideal, the two solder bridges 2-3 and 4-5, have to be put in place again.

The radio is a bit annoying what beeping is concerned. Julian G4ILO describes how to solve is issue.

Listening to my 10m MEPT (A1A), which happen to run today, I noticed a slight jitter in the PLL. I am not yet sure what this means and what causes it, I hope that this could be solved in the same way the PLL-jitter in the Target HF-3 was removed, by retuning individual sections of the frequency synthesis.

The radio employs the following modes of operation: FM, AM, USB and LSB. There is no CW. I noticed that between USB and LSB pure noise sounds very differently. Another indication that factory tuning may not be ideal.
The transceiver is provided with microphone and external speaker jacks. Digital modes, provided the jitter is gone, should therefore not be a problem.
The lack of CW, although kinda natural to a HT, kinda sucks. As soon as the bands are open again, I will use a keyed sine generator for transmitting CW using the side-band modes via the microphone jack. Due to the low locking speed of the PLL, QSK is no option... so what! Audio keying a transceiver has got an added bonus: power regulation can be done by audio level control.

Can't wait until CONDX provide us with open high bands, so I can have DX-QSOs whilst walking to work.

Thursday, April 21, 2011

Day to Night Transition

Just a spectrum I would like to share. It nicely shows the transition from day time propagation to night time propagation.

Tuesday, April 19, 2011

Skanti Marinetta TRP 1

I got lucky! Ever since I made my GMDSS-GOC, I wanted one of those:

Skanti Marinetta TRP 1 portable survival radio
In the Scheepvaart en Transport College Rotterdam, where I studied for the GMDSS-GOC, those units are on display. You can only guess how happy I am to finally got one into my collection of marine radios. The best thing on this purchase, the set is complete with all standard accessories.
I would like to thank Willy PA0WMR for keeping this rig in near original state. Willy also stated that the transmitter delivers about 5W on 600m.

What is all the fuss about a yellow box anyways you may ask. And the question is well justified. First of all, the box, with the lid closed, swims ;-) It is yellow! (That would be a reference to Douglas Adam's Hitchhiker's Guide to the Galaxy).

OK, lets be serious, why am I so happy to finally posses one?
Having a look at the manual/schematics we see that the rig
  • has a modern (digital) design
  • operates on 500kHz, 2182kHz and 8364kHz
  • is crystal controlled
  • allows for CW and AM
  • has a built in dummy load
  • employs an antenna current meter
  • contains an ATU
  • can create its own energy (by means of cranks)
  • can be energized by an external source

500kHz, 2182kHz and 8364kHz are (former) distress frequencies and must not be use by ham- radio operators! 

Where is the hamradio use of these units? Well, we all hope for the 600m band. The 500kHz signal is created by a  2.000MHz gate-XO and digital dividers. Depending on what band we will finally get, this crystal can simply be replaced by a fitting one. However, since it is a digital XO, on simply could remove the crystal and feed a DDS generated signal into the digital gates.

According to the schematics, the transmitter's 8364kHz crystal can easily be replaced by a 40m crystal. However, the receiver employs some resonant LC-stuff with varactor tuning, which should not pose a major problem to modify to 40m, e.g. 7030kHz.

The receiver uses a 2682kHz crystal oscillator to the 2182kHz emergency frequency. The transmitter employs a 2182kHz digital gate oscillator. We got two options for ham-bands here, 160m or 80m. Both have pros and cons. 2182kHz originally is an A3 frequency. The wiring inside the TRP 1 is providing AM modulation accordingly.
On the 80m band, AM is used in places, hence, that would be a nice possibility to join the action. However, filters will have to be modified.
On the 160m band one may want to aim for A1 operation. A 1.843MHz crystal would do the trick here... However, the wiring will have to be changed to engage the BFO in the "2182kHz" labeled switch position.

What is the prospect for the future use of the rig?
I believe it would provide endless fun during field day operations. In particular when operated from cranks, independently from any power supplies.
The (yellow) box contains everything needed for QRP-ops, including a telescopic vertical antenna and a "long(er) wire" aerial.

I figure it could be reasonable to replace the TBA570 receiver with a NE612 superhet design for side-band use.
The XOs could be replaced by either a DDS or some synthesizers for enhanced flexibility.
Some PIC controls seem obvious, the automatic SOS-TXing is inadequate, obviously.

It all comes down to how much modification is actually wanted. Maybe the greatest fun can be obtained when staying as close as possible to the original functionality, i.e. AM on 80m, CW on 40m and 600m.

Other than that, it is an extremely nice addition to my marine radio collection.

Thursday, April 14, 2011

Magnetic Loop Antenna Idea

Had an idea... again, I have not tried this yet.
A magnetic loop antenna, as we all know, are relatively narrowband. For mono-band QRSS, WSPR or WSJT activity this is not a problem at all. But what if one would like to receive (well, let's start looking at RX only at this point) on an additional frequency at the same band or maybe even in another band, such a simple magnetic loop antenna would not be so ideal.

Now that the problem is defined, let's have a look at possible solutions. The basic idea is to build two loops sharing one coupling loop by using heavy gauge speaker twin lead.

RF-principle: Two parameters determine the resonance of a magnetic loop antenna, the diameter of the loop and the capacitor.

For a second frequency in one band one may consider to shorten one cable of the twin lead by just the right amount. This will certainly result in a second resonance close to the first resonance. Since the two leads are somewhat close, there will certainly be some capacitive coupling, what influence this will have, if at all, will be subject to experimentation. The second consequence of the proximity of the leads would be that the lengths cannot be drastically different, hence, using the same capacitor, the frequency offset would be small.

For dual-band use, the two loops should be resonated by individual capacitors. Here, the capacity between the loops will certainly have a dramatic impact on the resonance frequencies.

There is yet another possibility, probably the most messy one... Connecting the second loop to the resonating capacitor of the first loop symmetrically using identical high(er) value capacitors. This will (slightly) increase the resonance frequency of the second loop. I figure, this third possibility is somewhat impractical.

Whatever option is chosen, the (single) coupling loop will couple both loops equally well, since the size of the coupling loop is defined relative to the size of the main loop(s), i.e. 1/6 to 1/4 depending on the loop's environment.

Wednesday, April 6, 2011

17m XTAL Controlled QRSS / WSPR / QRP / SDR

Sorry for having been silent for a while. Some new thought, although not entirely mine, I believe sharing it this way would be more than appropriate.
The idea about the frequency generation is borrowed from DJ1ZB. Ha-Jo uses CB crystals on their fundamental and doubles the result.

Doubling sounds very much like two things I previously disclosed on this blot, namely, the subharmonic direct conversion receiver (e.g. this) and the subharmonic I/Q-SDR (see earlier posts on the SDR and possible frequencies).
Both designs rely on a local oscillator on half the operating frequency.

Concentrating what could be interesting for QRP, QRSS and WSPR, lets have a closer look to the available crystals.
  • 27.105MHz (12T) => 9.035MHz x 2 = 18.070MHz
  • 27.135MHz (15T) => 9.045MHz x 2 = 18.090MHz
  • 27.155MHz (16T) => 9.051667MHz x 2 = 18.103333MHz
  • 27.165MHz (17T) => 9.055MHz x 2 = 18.110MHz
The frequency generated with a 15T-XTAL appears to be ideal for I/Q-SDR since the whole CW & Data & beacons range will be covered by 48kHz sampling rate. Have a look: difference 18.090-0.024=18.066 and sum 18.090+0.024=18.114.
Additionally, 18.090MHz is the quite close to the QRP frequency, a subharmonic direct conversion receiver would be an obvious choice, so would be a transmitter with a doubler...

Very obviously, the other frequencies are directed more to QRSS and WSPR. I am not going into the QRSS feature here, it is kinda trivial (see above).

Remaining topic: WSPR. The frequency produced by the 16T-XTAL is very very close to the WSPR "dial frequency" 18.1046MHz. With a Pierce oscillator the tiny amount of 633Hz upwards pull should not be a big deal; remember, on half the frequency, one only needs to pull half the distance.
RX: subharmonic direct conversion.
TX: subharmonic mixing of the local oscillator with an audio signal should create a DSB signal... that's the theory... I have not yet tried it yet, however, I fail to see any reason why this should not work.