Saturday, September 26, 2009

Ahhh, another source of noise located

Remember that stupid line in the lower third of the 30m QRSS spectrum? As said before, earlier tests have shown that is was due to the built-in sound card. For a change, I wired up my two diodes to the rear Mic jack, and guess what? No stupid line. My system has got two built-in sound cards one of which is O.K., and the other is c###.

Sunday, September 20, 2009

Grabber RX back to DSB

Due to reduced sensitivity, the filter-crystal is back out again. Consideration here: we are looking at a bandwidth of 100Hz. The received LSB will be (about) 10135100Hz to 10135200Hz. According to this document, there is just the occasional Feldhell QSO, but other than that, the LSB range of the DSB receiver seems to be an empty spot.

Sunday, September 13, 2009

HB-1A qrp transceiver

Recently, well, several weeks ago, I came across a neat little radio from China, the HB-1A qrp transceiver. Tempted to order one. Up to now, I could resist.

Searching the internet for more information, I found a schematics diagram (dated 8-Aug-2009). From available information and some guesswork, that's what my understanding of the rig is.

Digital Part
The trx covers 5-16MHz using a DDS (AD9834) controlled by a 16F73. There is a keyer in a 12F629 and a MAX522 dac for generating voltage for the receiver's variable filters (more on that later). Finally, a serial eeprom is wired up to the main controller, which also runs the LCD.

Nothing worth to be mentioned here, the keying looks a little unusual to me... There is one thing interesting however, no mixing is done in the transmitter, although the receiver is a superhet. It appears that the frequency generated by the DDS for transmit is the in band QRG.

Pretty straight forward NE602 / LM386 design. Muting is done by shorting out an attenuated (by a 2N7000) signal by means of a 2N3904. Here comes the first of the two variable filters, a tank-filter design using varactors driven by one of the MAX522's ports. NE602 front-end/mixer wired op to the DDS as LO. IF filtering is done by a variable bandwidth Cohn filter using varactors driven by the other port of the MAX522. A second NE602 used as BFO and product detector in the commonly known manner. The use of the LM386 is slightly unusual to me again, in particular the AF gain, or better volume control, which is done behind all amplification, with a potentiometer just before the phones jack.
No frequencies are given for the crystals, thus, my guesswork with some rough calculations came up with a likely IF of about 4MHz.
Thus, 4,1952MHz it is....

I am not quite sure if I understand the intention behind the relay placed in the low pass. If the transmitter would require an extra low pass filter, this could have been done directly behind the PA, overcoming the relay and in particular the noise it causes... clack clack de-clack...

Personally, I like the concept of the inclusion of the most important SW-BC bands. Seems like a nice companion for vacations, playing radio and receiving the daily news. Looking at the bands the transceiver covers (40/30/20), there will be propagation most of the time.

I was reading on an American page, that development seems to be going on for a version being capable of CW, SSB and DATA. Now, that sounds interesting!
Thus, I will wait for the time being, when ordering now, it wont be here for my next trip anyway.
But again, it's not really expensive... and why not... yeah well... hummm... we'll see about that ;-)

Sunday, September 6, 2009

off topic: AAO-110 accumulator charging (or not)

Strange, I thought, just a few months after purchase, the accumulators of my (several) Acer Aspire Ones (linux&win) seemed to have died. Hmmm, the one of the much older Eee4G still is doing fine. Very very strange, I thought, I tried to get free replacement from Acer, no success however.

Seems that I am not the only one having that problem. Internet revealed, it's not the battery that's gone dead, it simply the netbook not recharging it. In some micro-code, there's is something preventing the accumulator, when deeply discharged, to be recharged.
Actually Acer is aware of this, and made a new BIOS available, solving the problem. It is said that since BIOS version 0.3309 the problem is solved. I flashed version 0.3310 today, and yes, the problem is solved. The accumulators are charged again!

Up to now, I only flashed the windows one and gave an initial charge to the batteries used with the linux machines.

Thus, if you encounter a similar problem with the AAO (110/150), this could be your solution.

Saturday, September 5, 2009

New 2nd-Hand Toy: FRG 100 (aka Frog 100)

Finally, I could not resist. For various projects, e.g. 136kHz, I bought a 2nd-hand FRG 100 at my not so local "radio boer".

Seems it's got the FM option built in, however, no cw-filter and no tcxo.

According to the RSGB publication "LF Today",the receiver is as sensitive on 136kHz as the TS-850's receiver. This claim actually made me buy the Frog 100.
"LF Today" further reports on the modification of the SoftRock lite ( for low frequency use. More on that in a further entry.
However, I like the pointer to the SoftRock lite, since my plan was to include a SoftRock lite into the Frog. There is room enough in the casing,the second i.f. is 455kHz, thus, using a 1.8432MHz crystal in the SoftRock lite, resulting in a center frequency of 460.8kHz, will add a nice I/Q-SDR back-end to this nice piece of kit.

The lack of cw-filter could possibly solved by a 455kHz ceramic resonator ladder. I'll see about that.

Last point, the missing tcxo, that is a bummer really. Three ways to go, leave it as is and hope the best for stability, try to hunt down a tcxo (could be a tough one) or build a temperature controlled oven around the existing xtal.

Finally, I wonder if I could use the meeaouw port (c.a.t.-flap) for something meaningful...

Thursday, September 3, 2009

HF3, improved SSB filter

Was able to catch some Murata 455kHz ceramic SSB filters on *bay. Also looking into a CW-filter designs using ceramic resonantors. The RX, I believe, would suffer some improvement in terms of bandwidth...

Tuesday, September 1, 2009

U.S. 40m QRSS XTAL combi

On the KnightsQRSS-list, recently a discussion about frequencies went on. Stu and Dave pointed out frequency restrictions of various license categories. QRSS transmissions have been done on 7.105MHz, as far as I recall.

Using an appliance, one can set the rig to any random frequency, agreed, operating an MEPT homebrew-style, here are two options:
  • 7.106 = 10.106 - 3.0
  • 7.103 = 12.288 - 5.185
The 5.185MHz crystal used to be on a distributor's list I printed in May 2009, the same distributor appears not to be selling this crystal any longer. The crystal is still listed at DigiKey.

There is a somewhat more difficult approach however which would involve penning down crystals:
  • 7.105 = 11.0592 - 3.9542 (1.)
  • 7.105 = 11.000 - 3.895 (2.)
  • 7.105 = 9.202 (3.) - 2.097152
  1. penned down 4MHz crystal
  2. penned down 3.9321MHz crystal
  3. penned down 9.216MHz crystal
I hope this helps to promote the idea of QRSSing at frequencies accessible to all.

73, Joachim