Component Sources

[Albert H]

Does anyone have a cheap(ish) source of the POS150 VCO? I have a bunch of boards for PLL exciters that use these and I'd like to populate them and shift them (I have a potential buyer in the Czech Republic). I used to get them straight from Minicircuits themselves, but now they won't sell less than 100-off quantities. If I have to get a hundred of the things, I'd need to get another 75 boards etched! This would get very expensive.

If anyone's interested in how to do the simplest 1.5W exciter you've ever seen - one VCO block, two transistors, two voltage regulators, three ICs (a PIC, an SAA1057 and a 4049 for the 33V varicap supply), I'll put the details up here. It fits into a small Eddystone diecast box or into a standard tinplate box. Frequency selection is by jumpers (or DIP switches) and there are no other adjustments on the board at all. Peak mod is 1V5 p-p for 75kHz deviation (at any Band II frequency), and there's even a diode clipper to prevent over-deviation. There are no spurious products worse than -88dBc, so it's beats the hell out of any of the BW, PCS or pretty much any of the others.

We've used this board to drive rigs up to 80kW, and it remained stable (if the earthing was sane) even though it was housed in the same cabinet as the PA valve! LB uses these to drive a pair of the 70W Mitsubishi FETs for 120 Watts of completely unburstable pirate power. He also has 600W and 1.4kW PAs using Philips NXP FETs and these are proving popular in the USA. I still can't believe the astonishing efficiency of the latest generations of RF FETs!

[Analyser]

Sorry, can't help. I was always interested to a play with the POS150 and have a look at it's performance- by the sounds of it pretty good.

How come you need the 33V varicap supply? Looks to me like tuning in the FM band only needs a control voltage of about 4-9V to cover everything you need.

[Banus_radio]

id be very interested in the 4049 33v section if you wouldnt mind albert. Thanks in advance

[sinus trouble]

A neat little oscillator!
Looking at the datasheet it seems analyser is correct! you could probly control this device direct from any standard PLL? Not sure how it would affect modulation (if any)

Ive never seen this device before now and would be eager to try one if anyone manages to source any?

[Albert H]

How come you need the 33V varicap supply? Looks to me like tuning in the FM band only needs a control voltage of about 4-9V to cover everything you need.

Consider you want to tune a 20MHz range. If you're using your 5V swing to tune that whole range, that's 4MHz / Volt. That means that your modulation sensitivity is going to be insanely high, and the board is going to be very susceptible to hum. Even if you're using a second varicap for the mod, the control path will be picking up crud.

With the higher Voltage for the varicap supply, you can move their operation into their linear range - giving sensible sensitivity and lowered distortion - and reduce the risk of the dreaded hum. You can also reduce the number of varicaps required, giving a much lower noise floor too.

[Albert H]

id be very interested in the 4049 33v section if you wouldnt mind albert. Thanks in advance

I'll put it up here later on.

[Analyser]

How come you need the 33V varicap supply? Looks to me like tuning in the FM band only needs a control voltage of about 4-9V to cover everything you need.

Consider you want to tune a 20MHz range. If you're using your 5V swing to tune that whole range, that's 4MHz / Volt. That means that your modulation sensitivity is going to be insanely high, and the board is going to be very susceptible to hum. Even if you're using a second varicap for the mod, the control path will be picking up crud.

With the higher Voltage for the varicap supply, you can move their operation into their linear range - giving sensible sensitivity and lowered distortion - and reduce the risk of the dreaded hum. You can also reduce the number of varicaps required, giving a much lower noise floor too.

Right, but the POS150 has a fixed sensitivity of about 6MHz per volt, which I guess cannot be changed because it's sealed in a can. Also, the voltages needed to tune this thing are in the 4-9V range so you cannot "move" them into t a more linear range (I'm guessing the POS150 is quite linear anyway?).

So, unless you use a voltage divider to take your 33V down to 9V and this somehow reduces the noise?

[Albert H]

Nope - I don't want to use the internal varicaps - they're too noisy. As I recall, they can be strapped to supply to get to the top of the band, then the external varicaps can tune it and modulate it.

The other option is a TDK VCO which is even harder to get, but has incredibly low phase noise. It's the best module oscillator I've ever used, and one of those into a BF199 would drive a BLY33 or 133 to exactly 25 Watts at 14V supply - it used to be my standard RSL rig!

Stephen Moss and I experimented with various ways of getting rid of the trimmer capacitor in the NRG VCO - we used diodes to switch in capacitors as you tuned down the band - that worked well, but was fairly complicated. In the end, I took the Varicap supply up to 30V using one of the outputs from the 4060 to drive a simple single transistor SMPSU.

The next version of the board was going to include that modification, and rotary BCD switches to give direct read-out of set frequency. The output transistor was going to be a 1971, and that and the two voltage regulators would also have been screwed to the same grounded flange running right across the board. The heatsink would also provide a screen between the output filter and the rest of the circuit, and extended either side of the board to give mounting holes.

The prototype boards (we made three of them) gave 5 Watts at 12V, and could be steamed at 10 Watts with 16V supply and two component changes. The overall board layout was fairly similar to the Pro III, with the RF down one side and the logic at the other, though it was - overall - slightly smaller.

There was a better highpass filter coming out of the oscillator, and there was gain levelling to give exactly the same power output right across the band. The output power on the basic version could be varied from 500mW to 5 Watts - adjustable with a trimmer. The spectral purity of the prototypes was brilliant, and there was room on the PCB for a screen between the RF and logic sides of the board to reduce the already low carrier noise still further.

The final improvement was to bring all the LEDs to the "front" edge of the board, and they were all bi-colour - green for OK and working, red for out of lock, no RF out or supply out of spec. It was designed to fit into a standard aluminium box we'd found, which we proposed to use for screening inside the ready-built rigs.

I'll dig out all the notes, and put them up on here. There are also Gerber PCB files, so this could be a project for one of the Far Eastern PCB manufacturers.....

The component line-up was the usual PLL - though the 74HCT4059 was starting to get tricky to find - and mostly the same RF circuit as the Pro III with a few improvements and no VCO trimmer.

It might be interesting to do an updated version with a 16F628 and a TSA5511. With minor changes to the Hex files and coil and transistor changes to the PCB, we could make it work from 45MHz up to UHF! The board could also be significantly smaller.... Just had a thought - it doesn't need changed Hex at all - just use jumpers to select pins on the PIC for range!

There's a nice project for a few winter evenings!

[Banus_radio]

I googled the 4059 and found some voltage doubler circuits, but I also found some that use 555 timer ic, this is only 8pin compared to the 4059.

Is a 555 timer good enough to use, I want to feed npn from a tsa5511 pll, I will load it with capacitors to smooth it out. Or is the 4059 much better way of doing it?

[Analyser]

I googled the 4059 and found some voltage doubler circuits, but I also found some that use 555 timer ic, this is only 8pin compared to the 4059.

Is a 555 timer good enough to use, I want to feed npn from a tsa5511 pll, I will load it with capacitors to smooth it out. Or is the 4059 much better way of doing it?

That doesn't really make sense fella. The 4059 is a programmable divider IC and the 555 is a timer IC which can be used as a clock, but they're two totally different things. The TSA5511 is a PLL IC, again something else but you wouldn't use a 555 and/ or a 4059 plus a TSA in the same circuit.

What exactly are you trying to do?

[Banus_radio]

That doesn't really make sense fella. The 4059 is a programmable divider IC and the 555 is a timer IC which can be used as a clock, but they're two totally different things. The TSA5511 is a PLL IC, again something else but you wouldn't use a 555 and/ or a 4059 plus a TSA in the same circuit.

What exactly are you trying to do?

Sorry didnt make myself clear. I like to use TSA5511 as my pll, and i have a standard oscillator I use but the swing on the varicaps only covers 3/4 of the band using 0-15v.. So if I could use a voltage doubler then I would be able to swing using 0-24v (ish) and cover the band

Albert mentioned using a 4059 as a voltage doubler, I searched google for some circuits and found plenty of schematics for it but I also found plenty of schematics using a 555 IC as a voltage doubler..

So my question was would a 555 be ok to use as a doubler? or is it to noisey or any other problems. Id prefer to use it as it has only 8pin footprint.

[Analyser]

Yes, sure you can use a 555 timer as a clock source for a voltage doubler. The noise needs to be filtered after the doubler to prevent it appearing on the carrier but how noisy it is really depends on the method used to generate the voltage rather than the clock source.
Also, the IC which Albert mentioned was the 4049, not the 4059 which is a totally different chip.

[Analyser]

Just had a quick look onlne and people are saying that the normal 555 does actually put out a fair bit of noise but on the supply lines, so if you still want to use this IC then go for the CMOS 7555 instead.

[Banus_radio]

Thanks analyser, you really are the man
I will try tomorrow and post my results

[Albert H]

The 7555 is also pretty noisy.

[Banus_radio]

The 7555 is also pretty noisy.

So shall I order the 4049 then to try?

Maybe this circuit

https://goo.gl/images/kx27BS

[Albert H]

That'll do the trick! You might want to add another resistor (10k or so) in series with the output before it goes to the bias supply for the varicaps. Also be careful that none of the switching frequency ends up as ripple in the varicap supply - this will be a whistle that you won't get rid of!

[Analyser]

That'll do the trick! You might want to add another resistor (10k or so) in series with the output before it goes to the bias supply for the varicaps. Also be careful that none of the switching frequency ends up as ripple in the varicap supply - this will be a whistle that you won't get rid of!

Remember to pop your circuit up for reference Albert.

[Banus_radio]

Thankyou