The short video below shows a simple method for accurate tuning of a regenerative receiver, with the help of a small portable radio with digital frequency readout, 1 kHz tuning accuracy (or better) and SSB mode.
In my video, the regen receiver is the one described in some of my recent posts.
The portable radio is the Tecsun PL-660, that I recently bought on the web to use it for my first experiments as a MW DXer.
Please consider that I have made further modifications on my tube regen, always with the kind help of some members of the regenrx list on Yahoo. The up-to-date schematics is here below:
In particular, I have removed completely the wiring that I had added for the band switch, because it had resulted in a negligible improvement as a feature, while it had caused big problems in terms of spurious resonances that led the detector to demodulate strong local FM stations.
Now the tuning range is again the original 1330 kHz to 3735 kHz, but (thanks to a suggetion from Bernd, a member of the regenrx list) I discovered that I can move it down to approx. 730-2035 kHz, without any modification in the circuit or the tuning coil, by simply inserting a small pack of four ferrite rods in the core of the coil former. I suppose that the tuning range could be moved further down in the MW band by adding another ferrite rod in the pack.
That said, please find here below my short video about a simple method for accurate tuning of a homebrewed regenerative receiver. I hope you will find it of some interest for you.
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.
Today I have good news from my latest NDB listening session, which ended just a few hours ago, at about 3 AM UTC. In fact, I finally managed to catch my first transatlantic NDB DX by receiving the caribbean DDP-391 kHz, which is located in Puerto Rico at a distance of about 7560 km from my receiving station here in Livorno, Italy (grid locator square JN53em). My previous distance record was SAL-274 kHz located in Cape Verde Islands at about 4326 km from my home.
Recently I had changed my indoor loop antenna, moving from a Wellbrook ALA1530 to a Wellbrook ALA100 wideband amplifier, connected to an homebrew loop that I like to call "my X-antenna". It is briefly described here, in one of my previous posts. The receiver is still the small AFEDRI SDRNet 3.0, with HDSDR 2.70 as the software processor.
Aiming to receive my firts transatlantic (TA) NDB, I initially had oriented the loop towards Canada and North America, with the result of catching lots of French NDBs.
This night for me was the last night of CLE 187, the most recent Co-ordinated Listening Event organized by the NDB List, a wonderful and very active group of NDB listening enthusiasts on the web. I decided to have another try at my first TA DX but this time I thought it could be better to orientate my loop towards Gibraltar, so that to have as much as possible of sea water between me and the ancient "Pillars of Hercules", the entrance of the Atlantic Ocean. This way, the antenna ideally was pointing towards Caribbean Islands and Central America instead of Canada and US, but at least I could hope to skip part of French and Spanish NDBs.
Well, I would say my idea has worked. I know that DDP-391 kHz is a powerful transmitter (as it was SAL-274 kHz, my previous distance record). However, catching it has showed to me that TA DX is not impossible, even with my modest setup and in a period of solar maximum like the current one.
In next listening session, I will point the antenna in the same southwest direction again and I will concentrate in areas of the frequency spectrum were usually I see very few european NDBs (if any), mainly below 290 kHz and above 500 kHz, even if LW and MW broadcasts are a big problem in both ranges.
Nel mio piccolo, sottoscrivo e riprendo l'appello che il buon Andrea Lawendel ha lanciato dal suo blog Radiopassioni - in nome della ragionevolezza e della comune passione per la radio:
Le cartoline QSL sono le conferme scritte (tipicamente nel formato di una cartolina postale, da cui il nome) che i radioamatori - oppure le stazioni utility o di radiodiffusione - spediscono in risposta ad un rapporto di ricezione, inviato da un altro radioamatore oppure da un appassionato di radioascolto.
Sono molto ambite quando testimoniano la realizzazione di un QSO difficile o di una ricezione DX, ma costituiscono in generale un gradito ricordo, un pò come una foto di famiglia, specialmente quando provengono da paesi lontani.
Io non sono mai stato un collezionista di QSL. Il mio approccio al radiantismo è sempre stato più orientato verso gli aspetti tecnici e storici, piuttosto che verso la vera e propria attività radioamatoriale o di radioascolto, che in realtà pratico assai di rado.
Non di meno sono affezionato alle poche QSL che ho raccolto negli anni passati, soprattutto perchè mi ricordano la mia predilezione per la banda delle LF, un rapporto quasi affettivo che dura ormai da diversi anni. In questo breve filmato ne propongo una piccola carrellata.
Il radioascolto è uno dei miei passatempi. Il termine è abbastanza autoesplicativo e si riferisce in generale all'attività di ascolto delle trasmissioni radio, spesso provenienti da paesi esteri, talvolta da molto lontano. Gli obiettivi possono essere diversi, a seconda delle preferenze di chi pratica questo hobby, per certi aspetti singolare: l'arricchimento culturale (lingue straniere, visioni politicamente e/o culturalmente diverse dalla nostra, ecc.); la caccia alle stazioni difficili da ricevere (a volte indicata come DXing da DX che è l'abbreviazione telegrafica di distanza); la raccolta delle conferme di ascolto (in gergo cartoline QSL) che le stazioni inviano agli ascoltatori in risposta ai rapporti di ascolto; l'aspetto tecnico e tecnologico, che talvolta si accompagna all'auto-costruzione dei ricevitori radio, delle antenne; e così via.
Si può fare radioascolto praticamente su tutto lo spettro delle frequenze radio (ovviamente con apparecchi radio ed antenne adeguate per ciascuna banda) ed eventualmente prediligendo specifici tipi di trasmissioni radio: le normali trasmissioni di radiodiffusione (broadcast), i radio-amatori, le cosiddette stazioni utility ovvero dedicate all'espletamento di servizi (previsioni meteo, radionavigazione, ecc.).
Informazioni più estese e dettagliate sono largamente disponibili tramite numerosi siti web. Mi limito qui a segnalare come esempio i siti web di un paio di gruppi a cui sono iscritto (ma ne esistono sicuramente molti altri):
Dal mio punto di vista, il radioascolto è un passatempo talvolta affascinante laddove consente di venire in contatto con particolari tipi di trasmissioni che conservano un che di misterioso e rappresentano in qualche misura una sfida di pazienza e abilità. Nel tempo mi sono imbattuto in questo genere di segnali e talvolta posso dire di aver dato loro la caccia, cercando anche di costruirmi i mezzi (ricevitori ed antenne) per riceverli.
Nei prossimi post cercherò di parlare in modo un pochino più preciso di quelle mie (limitate) esperienze con la ricezione dei segnali delle number stations, delle stazioni VLF e degli NDB, la mia passione più recente.
