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lunedì 29 dicembre 2014

A beautiful introduction to regenerative receivers

Probably this will sound not new for many (if not all) enthusiasts of regenerative receivers, anyway I thought it could be still helpful for some (including me, of course) to read this beautiful introduction to construction of simple regenerative receivers from Gary Johanson, WD4NKA.
I have found it very interesting, informative and a real pleasure to read. In me it triggered a desire to start collection the parts for another regen, possibly built around a 6SN7 dual triode as described in the article.

"A 1938-1948 Era One Tube Regenerative Receiver" by Gary Johanson, WD4NKA

From by Gary Johanson, WD4NKA

mercoledì 24 dicembre 2014

SAQ Christmas Eve transmission 2014 on AFEDRI SDR-Net (VLF)

Today is December 24, 2014 and I liked to join in the traditional SAQ Christmas Eve transmission on 17.200 kHz (so in VLF), from the historical station located in Grimeton, Sweden.
This time I wanted to use my modified AFEDRI SDR-Net receiver together with my homebrewed 3-turns loop antenna. I placed the antenna outside on my balcony at 5th floor with south-north orientation. The antenna was connected to a LZ1AQ loop amplifier, build by Roelof Bakker PA0RDT, fed throgh a length of CAT-5 cable which also provided the necessary power supply. A passive 540 kHz low-pass filter was also inserted between the output from the amplifier cable and the receiver. The software running on the PC was SDR-Radio v2.3 (beta).

Below are some photos depicting the above-described setup.

The homebrewed 3-turns loop antenna (120 cm x 160 cm)

The LZ1AQ amplifier (built by Roelof Bakker, PA0RDT)

The AFEDRI SDR-Net receiver

The short video below is a panoramic view (from south to north, looking towards the sea) taken from my listening position in Livorno, Italy (grid square JN53EM).

Finally, the video below was taken on my PC during reception of SAQ transmission on 17.200 kHz. It shows how my modified AFEDRI can work pretty good at VLF.

domenica 21 dicembre 2014

Buon Natale, Merry Christmas

Tecsun PL-660, MW listening, etc.

Recently I felt the need for a simpler way to enjoy radio listening, compared to the usual way I do NDB chasing.
I mean, to listen to the NDB band on LF, I usually place my homebrewed "foldable" 3-turns loop in a sweet spot I found in the apartment (yes, I use it indoors); next, I connect the loop terminals to a wideband amplifier, then - by few meters of cable - to the receiver (an AFEDRI SDR-Net) and to the PC running the SDR-Radio software.
Of course both the AFEDRI and the wideband antenna amplifier need a power supply, to be connected and switched on; and finally I'm ready for my listening session, which usually lasts for 3-4 hours in the night, unless propagation conditions suggest to go to bed sooner than planned.
Well, while I'm pretty satisfied of the above-described setup, sometimes I'd like to simply switch on a more "traditional" receiver and have a couple of hours of pleasant, easy, relaxing listening to broadcast transmissions. By the way, this year I also decided to buy my first copy of the WRTH (the famous World Radio Television Handbook), to support my decision to "taste" the broadcast listening.
For the same purpose, a week ago I bought on the Internet one of these small portable radios, the Tecsun PL-660. I had already had the simpler Tecsun PL-600 model and it had worked very well for years. I had tried several modifications on it and it has survived to my soldering iron as well as to repeated disassemblies. It was still fully functional when I decided to sell it (at a fair price, of course). So, when I came to the decision to buy another portable radio, my choice has been for the successor of the PL-600, that is the PL-660.

My new Tecsun PL-660 portable receiver with a copy of WRTH 2015.

Compared to the PL-600, the PL-660 basically adds syncronous AM detection and the AM air band. Ergonomics were excellent on the PL-600 but have been furtherly improved on the PL-660. Overall, the value vs price is very good in my opinion.
I have made some quick tests of course on my new portable receiver as soon I received it. Most important weaknesses I have found so far are: the battery status indicator and the battery charger, which don't behave very well with normal NiMH rechargeable AA batteries (based on the "battery low" indication on the LCD display, it would seem they last much shorter than expected but I suspect the indication be wrong); and the reception in the MW band, which in my opinion is subject to easy overloading.
I have a 100 kW transmitter on 657 kHz (the Coltano station of the italian broadcaster RAI) within 10 km from my home. If I tune the PL-660 on the exact frequency, the reception seems to be not completely good, while it clearly improves if I detune the receiver by a couple of kHz or switch the built-in attenuator on the "LOCAL" position.
Uhm, this is a bit of a problem for my project to spend some time in broadcast listening. I have been a member of the MW Circle for a couple of years now and I was just thinking of medium wave (together with long wave) as the band of choice for my BCL activity (I always thought that shortwaves were too wide, too many kHz to surf, too many different kind of signals, too much stuff for me).
I think that an external tuned loop with good selectivity could help in working around this issue. I have a small square loop, that I had built with a "quick and dirty" approach for the PL-600. It is handy enough to be used as a table-top antenna. It has a 50 cm side and 19 turns of wire, closely wound on a square wooden frame. I also added a single turn to be used as a secondary winding for better impedance matching, in case of direct connection to the antenna socket of the receiver. The tuning range was from about 280 kHz to about 830 kHz, so mainly suitable for exploring the NDB band, but it could probably be moved upwards by removing one or two of the sections of the variable capacitor, that are currently connected in parallel. The Tecsun PL-660 does not enable its antenna input in MW (neither did the PL-600, I had to apply an HW modification to change this behaviour). So I will use the loop by coupling it inductively to the internal ferrite loop of the receiver.

My simple tuned loop antenna when I used it with the Tecsun PL-600

The variable capacitor connected to the primary winding.
The red wires are the terminals of the single-turn secondary winding.

Later on, if the new hobby will reveal to be attractive enough to me, I will think about a better antenna and maybe a better receiver (the system I currently use for listening to the NDB band will be the first candidate). For now, let's keep it easy (and cheap) as it was originally intended.

The video clip below is a quick test that I have performed with the Tecsun PL-660 during a short walk near my home. SSB reception on 20 m USB and 40 m LSB ham bands is shown, as well as in the AM air band and on MW (with the receiver tuned to the strong 657 kHz local station I have mentioned above). In the air band, following stations were recorded: Milano FIC (Milano Information) on 128.925 MHz AM, Roma ACC (Roma Radar) on 124.800 MHz AM, Pisa VOLMET (nominal frequency 128.400 MHz) on 128.390 MHz AM. The IF filter was set to "wide" in all cases.

venerdì 5 dicembre 2014

Long waves are getting poorer

Recently there have been rumours on the web that Polskie Radio will stop broadcasting on 225 kHz on March 1, 2015.
Personally, I read this information from the MW Circle group on FB (it appeared originally in the open_dx Yahoo mailing list), but it was reported also elsewhere on the Internet:

Berichte: Polskie Radio schaltet Langwelle ab

Roberto Rizzardi also remembered to me, in a post on the ndblist e-mail reflector on Yahoo, that - according to a report by Mike Terry (mwdx Yahoo group) - "The German national public broadcasters Deutschlandfunk and Deutschlandradio Kultur will disappear from longwave at the end of this year. Wasteful channels are going off the air due to cost considerations. The money saved will be invested in digital terrestrial radio (DAB+). At the end of 2015 the mediumwave transmitters of Deutschlandfunk will also close.
Deutschlandfunk currently still broadcasts through longwave 153 and 207 kHz and seven mediumwave frequencies including 1269 and 549 kHz. Deutschlandradio Kultur broadcasts by means of the longwave frequency 177 kHz. The mediumwave frequency 990 kHz went off last year".

As an european NDB listener, I could think this is not so bad news for the frequency range around 207 kHz and 225 kHz, where some canadian NDBs should become easier to catch, but of course it is sad to admit that LW are getting poorer, day after day. Is the history of long-haul radio broadcasting coming to an end?

The impressive 646 meters of Warsaw Radio mast in Konstantynów,
before its collapse in 1981 (Wikipedia)

mercoledì 3 dicembre 2014

Russian RSDN signals on my AFEDRI SDR-Net

Months ago I decided to replace the Mini-Circuits transformer (a type T4-1), in the input stage of my AFEDRI SDR-Net, with a pin-to-pin compatible type T4-6T, because of the bandwitdh of the latter being more suitable for reception of VLF.
Last night, at the end of a listening session dedicated to NDB chasing (and in particular to the evaluation of the LZ1AQ loop amplifier that I received recently from Roelof Bakker, PA0RDT), I thought I'd take a quick look at how my little reception system was behaving at VLF.
I was pleasantly surprised to see that it was possible to receive - at about 20 dB over the noise level - signals from the russian RSDN-20 navigation system (also known as the Alpha navigation system), on the three main frequencies of 11.904761 kHz, 12.648809 kHz and 14.880952 kHz.
The image below was captured while looking at the waterfall on HDSDR.

For the coming Christmas Eve, I was planning to listen to the traditional SAQ transmission from Grimeton on 17.200 kHz using a dedicated VLF antenna system. Now I think that I will try to do the same by using the same reception system that I'm using normally for LF and MW. A nice improvement.