Dual speed pll using saa1057

[shiva]

Hi,
i'm new here (and in the rf world)
i just read this thread.
just noticed that this pll design produced 1khz noise.
hope you guys find a way to reduce the noise.

i've bought 10 pcs of saa1057 online and its on the way. planning to build AM PLL for my sdr radio.
i got the schematic from fred's web. it said covers 512KHz upto 32MHz.
that will do good.
anyone have ever bulid this project?
when i'm finished building my MW PLL i'll post it here


regards,

[DJ Adam Eve]

 Perhaps it would be a good idea insert a choke (low pass audio filter let only pass frequencies below 50 hz.) in vco voltage control that stops the 1khz noise.

 We would have in this way the vco voltage control that don't change so quickly for be interfered for the bf choke.

 It's only an idea don't checked for me. I like the simplicity of this pll design, specially with the programmed chip because unfortunately there is many circuits diagrams publicated but most of them don't publicates the PICs code.

 Sorry for my poor english. Best Regards.

Yeah that's cool, thank for that reply. You may notice that else where in the forums is a post from me about this exact thing. Anyone else thinking about this fix would need to take in  to consideration the effect any capacitive element may have on the over all stability of the PLL (note the comment in Pira's original posting about not over loading the ouput with too much capacitance).

I have managed a work around for this.

ANyone thinking about this solution may consider a voltage follower at the PLL output.

[DJ Adam Eve]

Hello, I've just want to say that I've never had this problem your getting, I know that does help much, But I remember the First one I built did have a similar problem but this was due to the coupling capacitor  or C5 on the schematic being either not present to to low.  You can use greater value which will suppress this but I would recommend changing your varicap diodes to ones that have a smaller Capacitor scale i.e 1-10pf instead ones that are 1-40pf for example.

I dont now how you building these either, If your etched your own PCB or even the Pira template I recommend building these as a ( Birds nest or Spider wiring as some call it ) on copper clad board with a good solid ground plane with the components floating about 6mm  above the ground plane. this is a must for me as I build 150watt rigs using the SAA1057 in the same way as I described with no problems at all.

If you want help just email me on Junction@gmx.co.uk I'm more than happy to help and show you pictures of one I've built this way.

Regards

Will

I'm glad you never had this issue, but LOTS of people have, including the chip manufacturer Phillips. If you search hard enough there is an AN out ther regarding the possibility of phase noise entering the PLL charge pump. THis is due to the internal architecture of the chip itself.

Reducing the current has helped a little, as did playing around with the sample and hold circuitary.

Oscillator type also has a massive bearing on outcome, maybe you have just luckily ended up with the right oscillator?!

Changing layout has little effect, the noise is NOT picked up through tracks, or components but rather originate INSIDE THE PLL chip itself.

As for spider wiring (Ugly bugging) a PLL circuit: I wouldn't recommend it if avoidable, certainly not as a way of improving performance over a proper PCB! It inherantly requires longer leads than through hole, therefor results are a lot less predictable in RF circuits. My alternative layout is on here somewhere, and that was the start of me getting this one working.

As for the varicaps: I couldn't comment. But the issue isn't with tuning, or with stability. It's phase noise, so i don't really see that a smaller varicap would help, but i will look into it (my understanding was that the diode's capacitance was dependant on the reverse voltage applied to it, therefor a BB809 and a BB109, or BB909 would all demonstrate a tuning capacitance of {for example} 10pf, just at different points on a voltage scale).


Thanks for your reply.
AE

[shiva]

i have build the pll circuit.
the freq wont change.
i've try to change the freq by pushing the up/down button but it just change a bit.
the output rf is about 1800khz and stays there.

any idea?

[DJ Adam Eve]

Right, not sure what you mean... This design has no up and down buttons, it has DIP switches? Also this circuit puts out no rf at all, its a pll. The saa1057 can go down to 1.8mhz, but not with this firmware, thats designed to FM broadcast band. Are you using AM or fm?

If this isn't a design related to the pll perhaps you should start another thread?

Good luck!

[duivenmelker]

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i have built many transmitters using this oscillator using a BF199 with a wideband varicap diode and without the tuning capacitor and the original design from pira. They all worked very well without 1 khz tone or instability. The pll could lock anything from 88 to 108 MHz without manually tuning.

The secret is to set the pll to 88 MHz and bend your oscillator coil in a way the tuning voltage is very low (the lower the better) using a volt meter over the pll's tuning output for measurement. Now, the pll is able to lock any frequency up to 108 MHz. When you don't set your oscillator up like this, the pll might face lack of tuning capacity and therefor failure of locking to the desired frequency.

[duivenmelker]

[duivenmelker]

p.s. perhaps the varicap should get the highest possible voltage on 88 MHz. It was a long time ago i built transmitters and don't know for sure if varicap diodes increase of decrease in capacity when voltage is increased. However this is easily figured out by the given fact that at a lower frequency a higher tuning capacity is needed, so when comparing tuning voltages both on a high and on a low frequency will let you know how the varicap is behaving.

the amplifier stages in this schematic i never used, always use no-tune wideband stages. taking the pll's rf input from after the first buffer using a 10p capacitor for coupling. as a buffer i could recommend the bfr91 using the following diagram.

http://www.3-mtr.info/sales/Amplifier%20NoTune%20Profline%20300mW/Amplfier%2010mWatt%20-%20300mWatt%20rev%20A%20-%2028-06-2006.pdf

[duivenmelker]

here the transmitter as proven to work with the pira pll.
note: the 40p tuning capacitor may be removed when following the method as desribed in my former post.