Wednesday, March 31, 2010


The AN-100 dropped in today. TECSUN produces two slightly different MF multi-turn loop aerials for BC-receivers, the AN-100 and the more popular AN-200. My impression, it's just a matter of design. The AN-200 rests on a stylish arc-like stand, while the AN-100 is held by a rather non-stylish foot.

AN-100 from below

My preference was the AN-100, since I believed that the foot could be opened by a bottom plate, it seemed better suited for modifications. And, the dear reader may have a guess... I was guessing correctly. Underneath 4 rubber-foam pads, 4 screws allow access to the inside of the AN-100's stand.

screws underneath pads
Surprise surprise, the foot contains a polyvaricon, actually one of the type that is found in any random cheap broadcast receiver. The trick with those is, they employ little trimmers for basic frequency setting.

tuning capacitor
The modification to resonate the loop at 500kHz was consequently a simple one. One of the polyvaricon's trimmers was not set to maximum but rather to some odd looking position. Obviously that's the one to change. Well, guess what, I did just that, and the lowest resonance of the loop dropped to 494kHz.

Now, that was a simple one, no solder molten.
To drop the frequency even lower, solder needs to be molten. I figure a high quality, e.g. polystyrene, 47pF capacitor parallel to the tuning capacitor will do the trick.

The most upper resonance frequency is now 1330kHz.
The combination AN-100 & ATS-909 let me presently listen regular CW-QSOs.

inside the foot
Plenty of space in the compartment. Here are some ideas of what could be fit into this space:
  • a preamp
  • an I/Q-SDR receiver
  • a (subharmonic) grabber receiver w/ a USB sound-device, USB powered

Thursday, March 18, 2010

600m Transverter

The plan has been around for a while, ah well, since January, to build a transverter or at least a TX converter for HF to MF. Some ideas came along, some back a forth struggle, but finally, I soldered some components together. I have to admit, this design is not yet (!) tested.

This resembles a regular XOR Pierce crystal oscillator with an additional XOR for pulse shaping. As "filter and matching network", a second crystal is used. The drive level for the subharmonic mixer is adjusted by R3.
CR1 is a ceramic resonator for 500kHz. One could image to arrange a capacitors in series with it in order to pull up the resonator's response slightly.
In my junk box, there seems no indication for a 28.5MHz crystal, therefore, I consider using a regular LC resonant circuit, which is not yet figured out however.

Saturday, March 13, 2010

Bought a Telephone?

That was a good one... at todays radio flea market I was hunting for 600m marine transmitters or life boat emergency stations. No luck it seems. The one thing that came the closest to what those things would look like is the following device.
At first sight, this looked very very interesting, although, the Czech labels (now I know it's Czech) did not make any sense to me, this thing was bought. The 220/110V built-in supply made even sense for a lifeboat transceiver, since this box also contains an accumulator - actually the only word I could guess (AKUM.). And yes, there are emergency transceivers having A1A operation on 600m and A3H on 140m, so also the microphone made some sense. 
Closer inspection revealed however, that the inside of the box holds a bell! And what about this little crank the can be mounted on the right sidewall of the housing?
Here's a closeup from the front:
I like the way the Morse key is held in place, and next to it, a pen can be placed, ready for action.
All the stuff visible on the first photograph was actually in the compartment below the device. 
The compartment where the microphone is located contained four accumulators. Maybe not the win of the year, but fun nevertheless.

Friday, March 12, 2010

40m PSK-Warbler

Unpatiently I was waiting for my PSK-Warbler kit to arrive. Just in time, it did. Building it was very very easy, modifying it was relatively straight forward. Modifying? - you may ask yourself, yes, even a nice rig like the Warbler may be modified.

The Plan
Originally the Warbler is designed for 80m using color burst crystals for TX and RX ladder filters. For reasons of W1AW, the Warbler is using a b.f.o. above the filters' frequencies. Given that the Warblers are supposed to be used for PSK, this is an option, PSK-software can be set to operate on the lower side band. 
The modification described here is supposed to get the Warbler running on 40m, with as few changes as possible. The modified Warbler should also serve as a WSPR transceiver. Actually, this was the main point on doing this mod in the first place.

The Modification
This is what I did (please grab a circuit diagram):
  1. the b.f.o. xtal changed to 7.038MHz
  2. all filter xtals changed to 7.040MHz
  3. C13 -> 47pF
  4. L3 -> 10µH
  5. C10 -> 100pF
  6. C11,C12 -> 470pF
  7. L2 -> 1.1µH (17 turns on T37-2)
  8. C3 replaced by 2.2µH and a polyvaricon-trimmer in series
Points 1. and 2. are somewhat obvious, I believe. The crystals are available from Rich N4ESS.

Points 3. and 4. change the passband frequency if the C13-L3 series resonance circuit of the receiver to the 40m band.

Point 5. matches the coupling between driver and final to the operation frequency. This part of the mod may have to be revisited. 

Points 6. and 7. bring the low pass filter response to something above the 40m band.

Point 8. allows for variable pull of the b.f.o. to 7038600Hz. I used a combination of a polyvaricon-trimmer (4...18pF, I believe) and a 10pF NP0 capacitor in parallel. This is certainly the part of the modification in which some experimentation is required, since tolerances and different cuts or series capacitances of the b.f.o. crystal play a role in that game.

First Results
As I mentioned before, WSPR is certainly a main point for the little great rig. The first night out, RX only, at a hidden G5RV-jr, the following are among the decoded stations: VK6POP (14190km), VK6BN (14188km), W4PJZ (6781km), NB3N (6137kM), K4YO (5954km). 
I did TX, however, only once for testing, with very low power. For regular WSPRing, an enclosure would be required. Presently, the Warbler is laying open on the table, next to the grabber computer.
Next to WSPR many other modes were detected on the spectra, e.g. several types of PSK and even JT65. I am sure that the 40m Warbler will be a big hit! Dave K1SWL may put more on his webpage, stay tuned!

Wednesday, March 10, 2010

500kHz - AR3030 vs FRG-100

Did some testing lately, in order to see which of the receivers has got the edge. This book: LF Today: A Guide to Success on 136 and 500kHz indicates that the FRG-100 is seen as being as good as the TS-850. However, the TS-850 is attenuated from 500kHz upwards. The remarks in said book made me to buy a Yaesu FRG-100 some months ago. Prior to that I was able to ebay an AOR AR3030. The AR3030 gave good initial results on the Plumbtenna and the Octaplumb. But what a about a comparison?
In direct comparison the AR3030 gave a WSPR SNR 2dB above the FRG-100. So much to noise. But here comes some more.
In order to keep the receiver isolated from the soundcard, I was using a 1:1 audio transformer in the line. With good success on the Target HF3, which otherwise would have been totally useless.

When using the AR3030, I used the above mentioned cable with no further visible effects. A spectrum made at that time looked like that:
Some QRM, some WSPR, G3ZJO's MEPT, DI2AM, and some unknown signals. The SSB filter slightly kicks in on the upper range, but other than that, the spectrum looks quite "flat". Aerial at the time: Octaplumb.

And that's what the FRG-100 sees, (slightly different condx though) using the same aerial and audio cable:
The SSB filter (still set to 2.4kHz b.w.) cuts somewhat deeper, ok, but what is that bright range at 1.1kHz audio frequency??? I lived with it for a while. BTW, G3ZJO's WSPR at 2300z decoded with a SNR of -19dB, the strongest yet. Other than that, the typical signals are shown... but again, what is that elevated band at 1.1kHz?
As I have seen that Jan PA9QV, also using a FRG-100 meanwhile, does not see anything similar to that, I started looking for culprits. My first guess was the correct one, finally some luck in life. The isolating audio cable, that worked so well with the HF3 did it. Having it replaced now with a regular one (which came with a computer screen once), the sound-card now receives this audio:
A flat response, as received from the AR3030 with the isolation cable. Hmmm, it appears to me, that the "rec out" of the FRG-100 comprises some capacitance that, in combination with the inductance of the audio transformer, leads to a 1.1kHz resonance. Maybe useful to know, but not useful for a wide-band grabber. I could consider making use of that effect when going narrow-band at 1.1kHz audio.
Additionally, but this is not linked to the 1.1kHz issue, I widened the FRG-100's i.f.-filter to 6kHz.

BTW, the condx at time of that reception was very favorable in a NE direction. For the first time I received Radio Rud SK6RUD at 0233z.

Tuesday, March 9, 2010

DCTL relocated

The position as shown in the previous blog entry caused the DCTL antenna to pick up a lot of the TV-c###, erghh QRM. Also the position was rather visible and occupied another aerial's "mooring ring". Hence, relocation was required.
The new location is very low profile and still provides very good reception for the grabber receiver. My impression, the new location is much better than the older.

Sunday, March 7, 2010

DCTL update

Up to now my DCTL for the 30m grabber was not weather proof. Last week, I weather-proofed it by means of flexible installation tubing. The material I used is supposed to be inside the walls of a building. I supposed, it is not at all UV resistant. However, the materials seem not to have any adverse influence on the performance of the DCTL, as tested indoor. Now, all the tests done, I decided to give the DCTL an outdoor experience. On the northwards face of my house, UV won't be such a big deal, however, I would expect the tubing to discolor and become brittle over time.

Saturday, March 6, 2010


A couple of notes, not worth an individual entry, however interesting enough to share.

Changed from AR3030 to FRG-100, same aerial (Octaplumb), same computer, same software... (had to change the spectrumlab settinga bit). As a result, the AR3030 seems a have a 2dB SNR advantage over the FRG-100. This is the result from receiving G4JNT's WSPRing.

2.5mm² speaker cable is nice, works well in the Plumbtenna and the Octaplumb. I choose 2.5mm² because it was relatively cheap at a certain store. The same store also offers heavier gauge speaker cable, not precut, and somewhat more expensive. Namely 4mm² with red & black insulation for €1.79/m. Bought 10m for the outdoor TX loop.

Fillable sunshade stands make pretty good frame-antenna foots, indoors even when used empty. The frame can easily be rotated independently.

Plasma TVs suck!

Wednesday, March 3, 2010

ATS 909 vs AR3030

The Sangean ATS 909 is not a bad receiver, actually, I believe for the priece, it is a very good receiver. But, how good is it?
To find out, I did the following test:
  1. run the ATS 909 with the Octaplumb
  2. run the AR3030 with the Octaplumb
At the same frequency, measuring SNR (using WSPR) of stations receivable via ground wave.
On 600m, that was the result:

2010-03-03 21:26  G4JNT  0.503884  -11
PA1GSJ  406
 2010-03-03 21:22  PA3EGO  0.503927  +10
PA1GSJ  52 
 2010-03-03 21:14  G4JNT  0.503881  -22
PA1GSJ  406
 2010-03-03 21:14  PA3EGO  0.503923  -1
PA1GSJ  52

It seems, the AR3030 has got a 11dB advantage in SNR over the ATS 909. In other words, the relatively inexpensive ATS 909 is just 11dB short (in SNR) to one of the world's finest receivers.