8W + PLL + Stereo + RDS

[1608cc]

I made this build some months ago, and dig out from deeps of my room corner few days back during searching for something else... It is quite nice exciter so i decided to publish it

IMG_20240602_003652422.jpg

Basicly it is 8W @ 13.8V out amplifier based on 2sc1971 driven by 2n4427. The VCO is standard Veronica/NRG controlled by SAA1057 PLL. Data is loaded into SAA from attiny13 with small program incl. PLL lock state, without any displays and switches - all parameters are written into attiny eeprom. Stereo encoder is an old construction of polish pirates. 15kHz MPX filters are taken out form Unitra Diora tuner. Also preemhasis, input buffer, 38khz subcarrier correction are included in coder part. There are solderpads for RDS encoder, to be added in future (I have ordered pira.cz pic18 uC).

Still have to test everything under antenna. On dummy works very fine. Schematics, pcb, attiny software will post in following days.

[radium98]

Nice share

[Krakatoa]

Beautiful layout, compact and with a sensible distribution and shielding of sections.

[radionortheast]

I had a transmitter not so long ago that used the tsa5511, guess this is a similar ic, it had at frequency oscillator hum got into through the pll circuit, the rf amplifier was really uneven, while I could deal with that by using my own amplifier, I could not get rid of the hum, it is nice to see a good half frequency oscillator been used. I remember the veronica, I used have the 1w vco years ago, loved it more than anything it allowed me to hear music, gave me something to do on hoilday, not that far away but still good. I did think about trying to change the oscilator on the other transmitter, maybe ask on here, its beyond my knowlege, it ended up in the bin.

[1608cc]

Nice share

Thanks

Beautiful layout, compact and with a sensible distribution and shielding of sections.

The design is one-pcb, because I got nice alu enclosure from my friend, so designed everything to fit it nicely. Shielding is present on critical rf-circuits in all my projects - I have learned that lack of shieldwalls is a asking for a troubles.

I had a transmitter not so long ago that used the tsa5511, guess this is a similar ic, it had at frequency oscillator hum got into through the pll circuit, the rf amplifier was really uneven, while I could deal with that by using my own amplifier, I could not get rid of the hum, it is nice to see a good half frequency oscillator been used. I remember the veronica, I used have the 1w vco years ago, loved it more than anything it allowed me to hear music, gave me something to do on hoilday, not that far away but still good. I did think about trying to change the oscilator on the other transmitter, maybe ask on here, its beyond my knowlege, it ended up in the bin.

TSA5511/5512 is I2C controlled, SAA1057 is SPI and offers many more settings (charge pump current, s&h or digital phase detector etc.) - in my opinion the best old PLL IC for TXs.


I started to draw schematics - here is one of audio part (one channel). Buffer + preemphasis + MPX filter.

obraz_2024-06-02_165218133.png

[1608cc]

Stereo encoder + subcarrier level correction

obraz_2024-06-02_174219808.png

[BriansBrain]

I like the screening construction techniques.

[1608cc]

PLL + uC + software

SAA1057 parameters are saved in internal eeprom of Attiny13. "Word A" for frequency, "Word B" for pre-lock state (digital phase detector for fast set-up of frequency) and "Word B" for after-lock state (S&H phase detector for clean tune voltage).

obraz_2024-06-02_220128450.png

obraz_2024-06-02_221916700.png

software.zip

[rigmo]

Hi, veronika schematic you use?

[1608cc]

VCO + driver + 8W PA

PCB gerbers in attachment

obraz_2024-06-03_142851663.png

Hi, veronika schematic you use?

As mentioned before - modified Veronica/NRG design with 2sc1971 power stage

[EFR]

Where You did get genuine 1917 transistors?
Everything what I have ordered have been fake ones.

[King Croccy]

Where You did get genuine 1917 transistors?
Everything what I have ordered have been fake ones.

There are loads of Original 2sc1971 on aliexpress, most of them have had the legs cutoff short but they all work. One seller is even selling original ones and hes soldered new pins on so they are full length

[1608cc]

Where You did get genuine 1917 transistors?
Everything what I have ordered have been fake ones.

I bought old radio-alarm module which has 2sc1971, 2n4427 and mv209's in circuit. Also don't know the source of no-fakes. There are some on Ebay, but the price...

[EFR]

There are loads of Original 2sc1971 on aliexpress, most of them have had the legs cutoff short but they all work. One seller is even selling original ones and hes soldered new pins on so they are full length

I have bought these, and only some have been ok.

Dont ask about 25pcs pack of D18S20 temperature sensors..... All of them had same ID...

[thewisepranker]

...hes soldered new pins on so they are full length...

You should visit their other web shop, they've gone one better and soldered bits of solder in place of the pins so you don't even need to use your own.

[RF-Head]

[Albert H]

1608cc - that's a good bit of work. I like your use of screening between stages - always a good idea, and often underused by constructors. It's always a good idea to screen the lowpass output filter from the rest of the PA - just as you've done.

The 1971 is a reasonably good transistor, but these days I'd probably use one of the Mitsubishi 12V FETs in a broadband circuit - trimmer capacitors are getting expensive and scarce! The RD15HVF1 only needs milliwatts in for 15 Watts out in a single stage, and because the gain is so high, you can use broad tuning - covering the whole band without adjustment. You need a two-stage lowpass filter to get rid of the harmonics, but if you're going for a bit more power, you can put a pair of the FETs in parallel, and largely null the even harmonic products.

Our most recent driver (a commission from a manufacturer of valve PAs) uses a pair of the RD06 FETs in parallel to give 10 Watts at any Band II frequency. We use an AGC loop to keep the RF output power constant across the band by slightly varying the gain of the buffer stage between the oscillator and the output pair. When it's calibrated for 10 Watts from 12V supply input, you get 10 Watts at any frequency without adjustment. I was pleasantly surprised by the high efficiency of the FET stage - we get over 75% efficiency overall!

It's a great pity that the SAA1057 PLL IC is obsolete - it was a great IC, and could be used for all sorts of transmitters from Longwave right up to UHF (using a prescaler!). Your use of the AT-Tiny is a great idea. The code for those ICs is very efficient, and quite easy to write. However, I can imagine that some people trying to select their frequency will find it difficult!

[1608cc]

Yep - RD mosfets will be better in this (and probably most other) circuit. But got all these parts from one module, and want to build the whole TX in an old style

If use RD06 - I think mosfet equivalent to 2sc1971 - then 2n4427 stage is completely unnecessary. If I remember nrg VCO is ~50mW, which is enough to drive it correctly.

SAA1057 is still quite common in polish shops - you can get it for £1 - £1.5. Have a big bag of them

obraz_2024-06-05_131324814.png

[Albert H]

Perhaps you'll simplify the next one you build by using the FET!

You can increase the output from the twin oscillator (without compromising its purity) by increasing the supply voltage. I noticed that you've used an 8V2 zener to stabilise the oscillator supply. If you want a little more (or less) power, a simple solution is to use an LM317 variable voltage regulator IC, so you can set the oscillator supply voltage accurately. If (later) you want to equalise the RF output right across the band, you could use a simple diode probe to measure the amplitude of the RF output, and then use an op-amp buffer to adjust the LM317!

[1608cc]

If you want a little more (or less) power, a simple solution is to use an LM317 variable voltage regulator IC, so you can set the oscillator supply voltage accurately.

Good idea. Could use AVR timer/PWM or DAC output to do that.