SOUNDTX wrote: ↑Sat Jan 08, 2022 10:58 pm
Can I use KV1310/1330 inplace of the MV104?
Indeed you can! I have those in there currently and they work just as good!!
Another option Stephen Moss and I explored was to use zener diodes or LEDs as varicaps. The varicaps we'd used in various designs were shooting up in price, and they were becoming scarce - the big suppliers often didn't have any. I built a PLL Pro III test rig using reverse-biased 15V 1 Watt zener diodes to replace the varicaps. The tuning range was much the same, and the carrier was just as quiet. I then tried green LEDs for the varicaps - again reverse-biased. These worked reasonably well - until the potential difference across one or the other of them was enough for it to go into conduction! In the end, I compromised - I used the zeners for the PLL tuning, and the LEDs for the modulation! I found that the LEDs had to be painted black if light was falling onto them - in the workshop, under fluorescent lights, we got a low level hum on the modulation that disappeared when the LEDs were in shadow!
The (slight) downside is that the zener diodes give fractionally more noise on the blank carrier, but the price advantage was tremendous! If you're stuck for varicaps, give zener diodes and LEDs a go.
SOUNDTX wrote: ↑Sat Jan 08, 2022 10:58 pm
Can I use KV1310/1330 inplace of the MV104?
Indeed you can! I have those in there currently and they work just as good!!
Another option Stephen Moss and I explored was to use zener diodes or LEDs as varicaps. The varicaps we'd used in various designs were shooting up in price, and they were becoming scarce - the big suppliers often didn't have any. I built a PLL Pro III test rig using reverse-biased 15V 1 Watt zener diodes to replace the varicaps. The tuning range was much the same, and the carrier was just as quiet. I then tried green LEDs for the varicaps - again reverse-biased. These worked reasonably well - until the potential difference across one or the other of them was enough for it to go into conduction! In the end, I compromised - I used the zeners for the PLL tuning, and the LEDs for the modulation! I found that the LEDs had to be painted black if light was falling onto them - in the workshop, under fluorescent lights, we got a low level hum on the modulation that disappeared when the LEDs were in shadow!
The (slight) downside is that the zener diodes give fractionally more noise on the blank carrier, but the price advantage was tremendous! If you're stuck for varicaps, give zener diodes and LEDs a go.
There are also many current varicaps available, The only difference is that they are all SMT now!
These things are tiny but with some careful soldering? A pair of varicaps could be fitted to the existing pads!
It is unlikely i will re design the PCB unless there are some major changes? But it is something to consider?
Re: Sinus 1watt PLL
Posted: Sat Nov 19, 2022 2:47 pm
by XXL
Does this hum at all ? Every on frequency design iv tried hums. Half frequency never hums.
Re: Sinus 1watt PLL
Posted: Sat Nov 19, 2022 7:09 pm
by yellowbeard
XXL wrote: ↑Sat Nov 19, 2022 2:47 pm
Does this hum at all ? Every on frequency design iv tried hums. Half frequency never hums.
It's half frequency in the oscillator dude, the old Veronica/NRG design.
Re: Sinus 1watt PLL
Posted: Sat Nov 19, 2022 9:25 pm
by rigmo
doesn't the noise come from the SAA loop filter, i.e. the direct output from the PIC... that is solved with the 082 between...
XXL wrote: ↑Sat Nov 19, 2022 2:47 pm
Does this hum at all ? Every on frequency design iv tried hums. Half frequency never hums.
ALL exciters are susceptible to noise in some way or another? Sometimes it is not the exciter that is causing the noise! (Maybe associated PSUs or PAs)
From tests i have performed on a decent quality linear lab PSU, very little noise is detected!
I cant guarantee that you will have the same outcome?
Re: Sinus 1watt PLL
Posted: Sun Nov 20, 2022 4:25 am
by Albert H
The carrier noise on that type of circuit is very low. You have to make sure that your power supply is clean (a cheap Chinese wall wort won't give good results!). If you use a 3-terminal voltage regulator to feed the board, be certain to fit bypass capacitors (10n - 100n) to both the input and the output, both down to ground. I used to use the 7815 regulator, and actually solder 100n SM capacitors to its legs - this keeps RF out of the regulator, and considerably quietens things down.
Another trick I used frequently was a "gyrator" circuit (just a single transistor one) in the varicap bias supply, and sometimes in the supply to the Oscillator. This also reduces carrier noise.
I also used to supply the Vcc3 pin on the SAA1057 with 30V, to allow a wide tuning swing. I could (just) get rid of the trimmer capacitor in the oscillator, and have the circuit tune right across the band. Stephen Moss and I tried out that approach, and we were considering it for the next version of the NRG board. We derived the 30V from a simple oscillator and rectifier circuit (I've put it up here before), and it provided a worthwhile improvement. The next version of the PLL PRO was also going to have a more sophisticated phase comparator (but still made from discrete ICs). I have a nifty little circuit that I've used for years, which uses a 74HCT74 and a 74HCT00, and gives a really reliable locked / unlocked indication too. It has much lower phase noise than the 74HC86 EXOR gate that Stephen used for years.
Re: Sinus 1watt PLL
Posted: Mon Nov 21, 2022 6:41 pm
by rigmo
sinus trouble wrote: ↑Sun Nov 20, 2022 12:51 am
Impressive Rigmo!
Rigmo, What is that?
