OLD SCHEMATICS

[Zozo]

Albert if you know the correct type toroidal I can amend the schematic. The ones I have are similar size but green coated. Just cant identify them.

Maybe a fixed up filter on the output and possibly a perfectly workable design?

It is supposed to be a blue and yellow T37-17 core.

Nice one Bton-FM,

[Albert H]

Talking of old schematics. Is this one of the most copied RF Strip designs out there?

BCWB2-RF-STRIP.jpg

If you add a resistive network between the loop control voltage and the modulation varicap, you can get corrected deviation sensitivity across the band. You need to have a consistent C/Vr slope for your varicaps - usually Philips parts are nicely consistent. My varicap bias network has a mod sensitivity preset resistor that gets set when the board is constructed, and then the modulation sensitivity is the same (1.55V peak for 75kHz deviation) all the way across the band. This makes the exciter truly "no-tune".

The output part of the circuit needs a little bit of modification. It's best to do the impedance matching (to 50Ω or 75 (72)Ω according to your choice) first, then have a lowpass filter (with 50 or 75Ω in and out) which turns over just above Band II. There shouldn't be any products below the second harmonic, so the filter just needs to be configured to be -80dBc by 175MHz. It's sometimes worth having two versions of the output - some of my gear uses 75Ω matching instead of the usual 50Ω. The reason is that there are commercial helical filters (usually designed for reception) that can be used at low power that are matched to 75Ω.

Just as a point of interest - a 1 Watt stage at 12V has a natural output impedance of 72Ω, which will match through cheap low-loss TV coax to the 72Ω characteristic of a basic dipole or quarterwave groundplane aerial. My link gear (both TXs and RXs) always matched into 72Ω. The UHF stuff could make use of cheap, high gain TV Yagis and the cheap TV coax!

[Zozo]

Talking of old schematics. Is this one of the most copied RF Strip designs out there?

BCWB2-RF-STRIP.jpg

If you add a resistive network between the loop control voltage and the modulation varicap, you can get corrected deviation sensitivity across the band. You need to have a consistent C/Vr slope for your varicaps - usually Philips parts are nicely consistent. My varicap bias network has a mod sensitivity preset resistor that gets set when the board is constructed, and then the modulation sensitivity is the same (1.55V peak for 75kHz deviation) all the way across the band. This makes the exciter truly "no-tune".

The output part of the circuit needs a little bit of modification. It's best to do the impedance matching (to 50Ω or 75 (72)Ω according to your choice) first, then have a lowpass filter (with 50 or 75Ω in and out) which turns over just above Band II. There shouldn't be any products below the second harmonic, so the filter just needs to be configured to be -80dBc by 175MHz. It's sometimes worth having two versions of the output - some of my gear uses 75Ω matching instead of the usual 50Ω. The reason is that there are commercial helical filters (usually designed for reception) that can be used at low power that are matched to 75Ω.

Just as a point of interest - a 1 Watt stage at 12V has a natural output impedance of 72Ω, which will match through cheap low-loss TV coax to the 72Ω characteristic of a basic dipole or quarterwave groundplane aerial. My link gear (both TXs and RXs) always matched into 72Ω. The UHF stuff could make use of cheap, high gain TV Yagis and the cheap TV coax!

Thanks Albert, I found the the loop control voltage bit interesting regarding the method you mentioned for corrected deviation sensitivity. It would also be nice to have a true "No Tune" design, but I think I may be a bit to far down the rabbits hole to amend that part of the design without a major re-shuffle of the PCB layout in that section to introduce the components needed.

In reality the VCO core in the MC120 will have to be adjusted to bring the loop control voltage to an expectable mid range is my thinking to allow a good +/- voltage agility to the varicap, thus leaving plenty of headroom in both directions as needed in a typical working environment. Also any thermal cycling the driver board is presented with won't cause to may issues either.

The output section of the design I'm working on is as copied from the BW 1w Plus range they produced, which I "think" I have copied over correctly. I have gone with the original use of S18 Toko's. Well not really Toko's but the copies which I think are manufactured by "TFC Ltd" and not "Toko Inc". I know "Murata" bought out Toko Inc some years ago, and I'm not sure if they continued that product line, or just sold up the remaining stock until it was all gone?

BW 1W Plus Schematic:

BW-OUTPUT.png

I'm still only in the "Beta" testing stage with the boards I have, and any issues of design I discover can be addressed and amended in the final revision. Some areas have already been revised which didn't happen until after I order the sample PCB's.

Going back to the output section. I think I'll have to conclude my results after the initial first tests. Perhaps this would have to one of the "Factory Set" alignments done if I was to market these boards for sale as fully built items so to speak. I guess the cutoff response would be adjusted and characterized for the lowest operating frequency with a system impedance load of 50Ω.

Although I did intend this to be something that other people could build if they wished. But in reality they would need test equipment handy to fine tune the output stage. But to stay true to the heart of what I originally indented in the other thread on here, which it being an "Open Source" project.

[Albert H]

In Roger's exciter, C32 was part of the match, but also provided DC blocking. C33 was added to try to improve the 2f rejection. The first coil is part of the match, and the second is actually the filter. Despite Roger's claims, I never saw the second out of those boards at better than -40dBc. He'd tried to reduce the parts count as far as he could, whilst still getting a respectable result, to try to make for the smallest - and cheapest - possible board.

In his effort to get the VCO to tune all the way across the band, Roger ended up with an insanely high mod sensitivity, and the board was very prone to picking up hum. Also, as it was an "at frequency" circuit, it also suffered from dreadful RF feedback problems: A friend of mine in Ireland tried to drive a big valved PA with one of the BW PLL+ boards, and just couldn't get it stable. I gave him an NRG PLL PRO III, and that worked first time without any issues at all!

[Electronically]

In Roger's exciter, C32 was part of the match, but also provided DC blocking. C33 was added to try to improve the 2f rejection. The first coil is part of the match, and the second is actually the filter. Despite Roger's claims, I never saw the second out of those boards at better than -40dBc. He'd tried to reduce the parts count as far as he could, whilst still getting a respectable result, to try to make for the smallest - and cheapest - possible board.

In his effort to get the VCO to tune all the way across the band, Roger ended up with an insanely high mod sensitivity, and the board was very prone to picking up hum. Also, as it was an "at frequency" circuit, it also suffered from dreadful RF feedback problems: A friend of mine in Ireland tried to drive a big valved PA with one of the BW PLL+ boards, and just couldn't get it stable. I gave him an NRG PLL PRO III, and that worked first time without any issues at all!

Albert speaking of Roger. Was his nick name jolly Roger?.

Sent from my AMN-LX9 using Tapatalk

[Albert H]

Way back in the early 80s when I used something similar to this exciter strip, the transformer was wound on a ferrite bead! It was two windings twisted together and then wound through the bead about 8 times. It worked just as well as the type 17 toroid, and cost about a tenth of the cost of the "polo mint"!

The other thing about that circuit was that they were usually built to fit inside small folded aluminium boxes (that came from H L Smith's in Edgware Road and cost 40p!). The PLL was either the CMOS trick or - later on - the SAA1057. The very first PIC code I ever wrote was to load the data into a '1057, and used a 16C54 one-time writeable PIC! I realised that I could use the 4 MHz rock (reference for the PLL) to clock the "A" version of the PIC, and saved quite a few parts that way. The PLL was under the board, and later versions used the S18 or MC108 - series Toko coils.

Roger got hold of one of our exciter boards, and copied the RF side of it (though he changed the varicap modulator a bit for a bigger swing), and he added the Motorola 145170 PLL and a 16F54 (with code nicked from the American "PLL experimenter" boards).

I never aimed for more than about 500mW out of one of these boards, because I'd usually feed it into a 2SC1971 for about 5 Watts to drive the PA. They were surprisingly clean for the cheapest of cheap exciters, and we churned out hundreds of them!

[Phoenix]

Remember buying trays of TP1028 and another stud output device from J Birketts
Think they were in Lincoln

And 2N3866

[Albert H]

Birkett's was a brilliant shop. I went up there to see what John had on offer, and he had these transistors that looked like 2N3375s. They were called 587BLY, and he said that they were only good for HF. He had a few dozens of trays of the things. He gave me a couple to try out. I experimented a bit with them, found out that they would handle up to 35V collector / emitter (by blowing up the first one!).

I found that with about 7 Watts of drive, they'd do around 90 Watts out on Band II!

I came up with a 28V PA strip that used a 2N3866, 2N3375 and a 587BLY. 100mW in would give the magic 100W at 31V when the trimmers were really carefully peaked. A more realistic power out - where they would withstand any mismatch - was at 28V, where I got a consistent 90W! I did a nice little PA PCB, and found a cheap source of Redpoint heatsinks. I was getting "batch tested" 2N3375s for 40p each (from Manton Lane Texas Instruments), the 2N3866, the trimmers and the 587BLY from Birkett, and was building 90 Watt PAs for <£8 each! I bought well over 1200 of those transistors from Birkett, usually for about £1.20 each!

The exciter that drove these PAs was a four transistor job (all BSX20) and there was a 74HCT CMOS PLL to keep it stable.

I built PAs with those 587BLYs with two and four of them in the output, with the bigger one using a single device to drive the quad! The 4-device version did around 320 Watts!

[teckniqs]

The high power 587BLY is in the same small package as 2N3375/2N3632??

....A quick Google image search wasn't helpful and the first thing that comes up is a photo of a nasty clad board driver I posted lol.

[Albert H]

Yes. The 587BLY was exacly the same package as the 3375. They were used in aircraft transmitters (we found out later). Roger used to drive them with a 2SC1945 (he couldn't get the 3375s at a sensible price). I think that I've still got a few of them - I'll photograph one if I can find them.

John Birkett was right - they were great at HF, and had loads of gain. I built a couple of 6.4MHz linears with them!