Low VHF OIRT band - June 2022

Living far away from those Countries that use(d) the FM OIRT band (65.8-74 MHz), it is hard to tell if it is still used nowadays. But with the help of Sporadic-E propagation you should receive few stations if you are lucky.

The video below shows my unscientific band scan on 2022-06-10 at 1705Z, while the path had been open for an hour or so. The antenna was the humble 4 element beam on the balcony facing East.

The language sounds Russian. I patiently waited for advertisements and I could grab the word "Bielorussia", White Russia. I am not sure of the frequency because my 706 is getting old and a bit off, plus I might have heard several transmitters of the same station in different locations.

If you can identify the stations please leave a comment.

 

 

70 MHz progress - August 2014

Thanks to some amazing Es openings last July 2014, my 5W and Moxon beam allowed me to reach 7 DXCC (I, G, GM, ES, 9A, OH, YO) and 8 different squares.

Few more countries should be possible, even though I probably need to move the antenna to the balcony facing South to work EA and CT. Or build/use a second antenna and run a coax through the whole apartment.

Now that the Es peak is gone I can concentrate in working neighbouring squares, like JN34 and JN45. The only station I heard from JN45 is a big gun and we will arrange a JT65 QSO, possibly with the help of aircraft scatter, because 2x SSB was not successful.

Like a child on 70 MHz

The day after Italian HAMs were allowed to use 70 MHz band again for a few months in 2014, I reconnected my transverter and erected the dipole on the balcony. I tuned the band checking the local beacon with my ears and looking at the DX cluter with my eyes: the band was open.
All of a sudden I heard someone distant having a QSO. Disappeared. QSB was very fast. Then another voice, very strong, GM4JTJ, that came back to my 5W SSB balcony signal! Hooray!

I felt like 25 years ago, when as a child I worked my first DX'es on CB channels. I kept tuning, calling CQ, tuning, trying to ignore the female voice(s) calling me for dinner. But this time it wasn't my mother's voice, it was my youngest daughter's reminder that dinner was on the table.

I walked to the kitchen, explained that a unique event was going on, an event that happens 4-5 times a year and doesn't last long. When returning to the shack I got the familiar "don't complain if there won't be food left for ya", this time thrown at me by the older daughter.

It was a funny parent-child-parent role inversion.

In the following days I came up with a quick way to explain propagation. You must have seen Stargate movie to understand it: sporadic-E looks like a wormhole opening to some random part of the world.

Now waiting for another randomic wormhole...

My Moxon beam for 70 MHz

I like the compact design of Moxon 2-element directional antennas, even if they are harder to build than a normal Yagi. Given the fact that 4 metres in Italy are allowed year-by-year, I do not want to invest in a large antenna, and I believe the gain of a Moxon should be enough to take advantage of sporadic-E openings.

Last year I had started building one and almost forgot. Then yesterday I had a pleasant surprise when I realised that everything was ready to erect the antenna and measure SWR! The only "problem" was how to hold the two wire ends pointing at each other.

Problem solved with two rubber bands cut open and secured to the wire with simple sticky tape!

The H-shaped frame is made of 20 mm PVC pipe screwed together with slightly modified Tee joints.

A huge storm was approaching, but wind was light so I could lift the antenna on the fiberglass telescopic pole on the balcony, measure lowest SWR at 66 MHz (1.6:1 at 70.2 MHz) and take the picture above.

Both local beacons were off-the-air, so I could test the extra gain.

Then the storm came and it offered a good opportunity to experiment with the camera:

Monitoring transverter output

Without a correspondant to try a QSO on the air, I had to test my 70 MHz transverter output with my own equipment.

First of all I used the RTLSDR dongle to record my output, so that I could easily play it back afterwards for a self-audio-quality check. Easily done, with the transverter transmitting into a dummy load in the shack.

Then I wanted to check for harmonics at 2x, 3x and so on: the RTLSDR tunes much higher than that. So I moved the output to the 70 MHz dipole and started calling CQ, while RTLSDR receiver was running on the computer screen. Look at what appeared:

That's the fundamental and two noticeable splatters about +/- 200 kHz away, about 30 dB below the center frequency. What the ...?!??

Checking at 140 MHz and 210 MHz the remaining signal was not too strong, spurs obviously following. If I transmitted in FM there was no splatter whatsoever, nowhere.

That's when I remembered an article by SM5BSZ about the (mis)use of ALC in the FT817 (search for "The abominable ALC"), which creates heavy splatters, especially at lowest power settings. While they are barely noticeable in the HF noise, they pop up in VHF and do annoy neighbouring stations!

So I checked the FT817 output at 144 MHz USB, 0.5 W output, and spurs were there. No surprise. My RTLSDR does not tune down to 29 MHz, my 4 m transverter IF output, but I bet the situation is not different.

Since you always have to doubt the bounty of your test equipment, and a 15 USD TV dongle should not be over estimated, I cross-checked with a true receiver: splatters are generated for real.

A quick check at 5 W output has shown that the FT817 doesn't behave acceptably better. One solution, that would improve my '817 in any case, is to change the ALC timing with a hardware mod. Otherwise I will have to drive the transverter with the IC706MKiiG, but SM5BSZ pages contain a warning about a full-power spike when PTT is pressed...

Transverter PA: self-oscillation solved

Fortunately it took little effort to tame the self-oscillation in the (PA?) 10-to-4 transverter. First troubleshooting action was decoupling the DC supply to the whole transverter board. I used a PI network composed of 2x100nF, 2x1nF and one VK200-like inductor.

The inductor goes in-line with the positive voltage. Then 1nF//100nF at each side of the RF impedance.

If you land on this page for a similar problem, don't go crazy looking for the VK200 choke. Try winding as many turns as they fit on an anonymous toroidal core recovered from some switching PSU, or a molded inductor or whatever will exhibit enough inductance and low enough DC resistance. I used disk ceramic capacitors.

But it is not the end of the story. [Note to the casual reader: what follows applies to this specific transverter board]

After correcting the self-oscillation, current drain was above 40 mA. Not bad, but I had measured 24 mA.
When I connected back the transverter PTT control to Arduino, the XV went into TX. This means that the 5V from Arduino is not high enough for the transverter circuitry. I added a BJT buffer and everything went back to normal. I just needed to update the sequencer firmware.

On-the-air test to follow!

Transverter boxed. PA self-oscillates

The Ukrainian 4m transverter has been installed into the final box, including IF relay and A*duino sequencer. The container is a repurposed manual KVM (Keyboard, Video, Mouse) switch and pre-drilled holes hold flanged BNCs just right. Also the VGA connector was a good a sturdy way to bring data from the FT817, pre-wired:

The smoke test did not produce actual smoke, but the current drawn is close to 1A. Considering the transverter should be in receive mode, that's not normal. Leaving it on a few seconds the Mitsubishi PA final warms up, so it is probably self-oscillating somewhere.

I have never troubleshoot a self-oscillating PA, just quickly read about it. I am thinking of two causes: either the DC supply cord is too long and lacks decoupling or the transverter board is too close to the box/ground.

Transverter sequencer with Arduino

Even if not explicitly mentioned, I decided my 70 MHz transverter needs a switching sequencer. Any existing solution I could find online uses either discrete components and ICs or a microcontroller I cannot handle (PICxx series).

Given the widespread availability of Arduino derivatives, their low cost (< 10 USD) and their extreme flexibility, I preferred to go down this route. Besides, an Arduino board allows for easy firmware changes (just plug it to an USB port of a computer!) and can be programmed for CAT communication with the FT-817 and alike (FT-857, FT-897, FT-100).

The sequencer code uses a level change interrupt (on INT0) to monitor the PTT line output on the CAT port ("TX GND"). This line goes to logical low level when the PTT is pressed

Once a transition RX-to-TX is debounced and detected, the main loop switches in sequence the IF input attenuator (not needed in RX), the transverter PTT and enables RF output on the radio (pulling down the "TX INH" line). Small delays allow for each change to be applied by the involved circuitry, being the relay the slowest to react. The TX-to-RX transition reverses the sequence described above.

At startup the sequencer inhibits RF output and configures itself in RX mode.

This is not rocket science at all.

If another output is needed it is just a matter of adding few lines of code. An extension to the code should allow to switch the RTX to the IF center frequency (29.200 MHz USB in my case) as well as make sure the FT-817 RF power is the lowest possible. Then drive a status LED, monitor the transverter PA temperature, ...

Transverter 29/70 TX'es fine

In a careful hurry I checked the 4 m transverter if it is suitable for SSB traffic.

Since it must be driven with 100 mW, a 7 dB attenuator was built so that FT817 500 mW would not fry the mixer stage. A "real-world" 7 dB Pi-attenuator consists of a 2W 120 ohm resistor across, 47 ohm straight, 120 ohm across. I used standard carbon resistors and a quick check with MFJ-259 reported a 1.2:1 SWR max up to 170 MHz.

With full manual switching I listened to my whisper transverted to 70 MHz on a different receiver and it sounded good.

This was the "GO" signal to start planning for a sequencer (probably embedded into one of my I-F-R-K accessories) and a suitable box: this time I will have to do the mechanical work!!

Transverter 29/70, RX current consumption

I found no mention online about current draw of the Ukrainian 29/70 transverter: my specimen drains about 24 mA at 12V in reception.

More to follow, especially a TX test once I found what is a suitable heatsink: just the containing box (yet undefined) or something larger?!

If everything works, the construction of a simple sequencer will follow. Most probably based on one of my (I)FR(K) projects.

Transverter 29/70 arrived and switched on

The "ten to four metres" transverter has arrived from Ukraine. The very first impression is that it is indeed SMALL! A picture-to-real comparison with the original 10-to-2 m transverter shows that coils are different, so it has somehow been retuned to 70 MHz. Look at it on a 5€ note:

First on-air test was the reception of the local beacon. I started closing the output on a 50 ohm load "just in case" (yes, I know the load shown is not able to handle more than 0.5W). Then about 4 m of RG58 going to the FT817 tuned on 29 MHz: the local beacon was coming through S7, with the dummy load as antenna! Actually, dummy load or not, it made no difference.

The transverter circuit is very very very simple (and I have spotted one error on the included diagram), but the RX chain is hot. Using the same coax length on the IC706 tuned to the beacon frequency resulted in the same signal strength. So, apart from RF leakage, it is a (good?) sign of life.

Transverter 29/70

While searching online for parts for a 70>23 cm tripler I came across an auction for a 10m to 4m transverter board. Just the fully assembled board and an A4 sheet with instructions.

It is supposed to output 5W on 70 Megs with 150mW drive on 29 MHz. It should be all-mode. It needs a heatsink, housing, wiring, IF attenuator and RX/TX sequencer.

Looks like a good companion for the FT817. Time will tell, since I bough one of those.

Edit: (At the time writing there is one board left in Ukraine)

TX-only transverter for 4m - with mixer

The picture shows my TX-only transverter with the diode ring mixer (SBL-1 or ADE-1) component added. The circuit has not grown a lot, but it does indeed work.

The canned oscillator is now terminated in a 1kohm trimmer and feeds the IF port of the mixer. RF from the HF transmitter goes to the LO port. Trimmers will most probably be replaced with fixed resistors.

As a signal generator I used the FT-817 at 24.9 MHz. Listening on a panoramic receiver I could clearly hear LO-HF (20 MHz) and LO+HF (69.8 MHz). The frequency counter on the mixer output picked up the LO-HF difference, which was expected since there is no bandpass filtering afterwards.

I tried swapping HF and LO signals but the result was the same. Signal output decreases if the HF trimmer reduces the mixer drive.

Next step is to build a resonating termination followed by an amplifying buffer. G3XBM circuit calls for a BF199, which is already sitting on the workbench, committed to take part into this project.

TX-only transverter for 4m

While I have no news about a possible 4m allocation for Italy in the next months, I have started working on my TX-only transverter - a "txverter"? - for HF-to-70 MHz.

The idea behind this project is that the IC706MKiiG receives on 4m, so there is no need for a full transverter, provided the operator accepts to operate split. It is a KISSAL principle: Keep It Short Simple And Lazy :-)

I decided to replicate G3XBM's simple transverter, TX chain only. I will build it manhattan/dead-bug style using an ADE-1 passive DBM mixer.

The picture shows first components placed on the copper clad board:

• 5V voltage regulator
• canned oscillator @44.900 MHz
• HF input attenuator of about 30dB (50, 680, 100 ohms)

Current drain at 12V is about 18mA, all for the voltage regulator and the canned oscillator.

The output of the latter is not a sine wave on a 100 MHz scope&probe, but it swings 0-5V if left floating.

I plan to blog how the circuit grows and how it performs.

Looks like ...

... Italy will get again a 70 MHz (4m) allocation in 2010.

I need to build an antenna again! And maybe a power amplifier for my 100mW CW TX.

Stay tuned!

4m contest: been there, done what?

Last Sunday I managed to take part for a couple of hours in the "70 MHz and Cross-Band Contest 2008" promoted by ARI Roma. I was in a nice place, open towards most of the Italian territory with no band noise and managed just one (local) contact.

Setup was as follows:

• RX IC706MKiiG
• TX homebrew CW 100milliW
• Antenna 4m Moxon
• Antenna 6m car whip

from the parking lot of Santuario di Belmonte, JN35TI at about 700 masl.

Activity was null, even if the band was open with sporadic-E to Greece. I could easily work Adriano I1NAI in 4m cross-mode. At 9UTC I was disappointed nobody was around, the parking lot was going to be filled with a FIAT 500 event (QRM!!), so I headed back home.

Adriano stayed a bit longer on the air, but he did not manage other QSO's either! Were all Italian operators busy with the HF Contest delle Sezioni? Are Italian ops not interested in a new band?

I could produce three short movies with the Samsung SGH-i780 :
http://www.youtube.com/watch?v=HF4A7X7ZtW0 (location summary)
http://www.youtube.com/watch?v=K13WVOsIc14 (receiving SV5FOUR/B)
http://www.youtube.com/watch?v=owjugPODRhg (receiving IZ1DYE/B)

Even if I had had more power I would have not had more contacts, but a small 1-2W PA will follow on the workbench.

Has anybody the QSL info for SV5FOUR/B?

70 MHz activity alert!

Segnalo la mia possibile attività domenica 15 giugno 2008 mattina, in occasione del "70 MHz & cross-band Contest" promosso dalla sezione ARI di Roma. In caso di bel tempo dovrei essere in JN35TI con i miei 100mW e la due elementi Moxon (piu' dipolo in 6m). In caso di maltempo, da casa JN35TC, sul balcone. Per sked o altre info scrivetemi!
!! Per ora posso trasmettere solo in CW; RX all-mode !!

On 15/June/2008 morning I will most probably take part in the "70 MHz & cross-band Contest" organized by ARI Roma. If the weather is good I will be in JN35TI with my 100mW and 2 element Moxon (plus a dipole for 6m). In case of bad weather I will stay at home in JN35TC. Write me for a sked or other info!
!! I can transmit CW only; RX all-mode !!

Primo QSO in 4 metri

Il primo QSO o qualcosa del genere, ieri sera 05/06/2008 a 70304 kHz alle 20UTC circa, cross-mode CW/SSB.

Avevo modificato la configurazione del keyer in IAMBIC-A, e non riuscivo a mandare correttamente i simboli (ah, il buon vecchio tasto verticale!).

Povero IZ1DYE con tutta la confusione che ho fatto! Abbiamo concluso il QSO al telefono, ma i segnali erano presenti.

QRB: 32km. Moxon contro dipolo, 100mW contro qualche decina di W, CW contro SSB.

Qualcun altro vuole tentare il QSO? Anche cross-band. Io trasmetto solo in CW, ma ricevo all-mode in 50 e in 70 (e in 144, 430, HF). Sono penalizzato in direzione 110-140 gradi, a meno di andare di riflessione sulle Alpi. Vi aspetto numerosi!

Grazie Michele!

PS: perche' mi sta passando la voglia di imbarcarmi nella costruzione di un finale RF piu' potente?!

Primo rapporto in 4 metri

Giusto il tempo di programmare il keyer, avvisare Adriano NAI ed ecco il primo rapporto di ascolto del mio trasmettitore in 4 metri. A 35km il segnale e' ottimo.

A causa della pioggia improvvisa alle 22 e' invece saltato il tentativo con DYE.

Promette bene. Ed ho anche in testa l'idea di realizzare un amplificatore per avere un paio di W...

70 MHz, and the antenna is up!

Italian HAMs got a new authorization to use small portions of 70 MHz until 31/12/2008. The TX was already completed, now I needed the antenna I never finished.

The Moxon rectangle was chosen. A wooden "H" structure supports the wire. Lowest SWR is around 65 MHz, 2:1 at 70 MHz. On the balcony it looked like this:


Here it is beaming about 30deg. The tower is the background, for the locals, is at CSELT/TiLAB/whateveritiscallednow.