Hi All

Im just wondering if anyone could tell me the value of the resistor on RFC1 on the NRG PLL PRO III BOARD. I suspect it will be a 220 ohm 1 or 2W with about 13 turns on it, could anyone conform this please.

Chris

Almost correct, it’s 2k2 1/2watt carbon film with 13 turns and a ferrite bead on each leg before inserting it into the board.

thankyou very much, it was the only component had no info on


Chris

Surely 220 ohm will make more sense ? Can’t see what a 2.2k would achieve ?

220ohm or similar can be used for damping ??

Actually I didn’t look where rfc1 is on the board and don’t gave access to a diagram .
I’ve guessed it’s powering the final stage ??

It’s just before the collector to the 1947, it acts as a choke to stop RF getting back onto the power rail. The value of that resistor I think could be different depending on the batch of kits and date sold. I have a pro3 which was purchased from the original NRG back in mid 2010, they went out of business the following year in 2011. The board I have uses a 2k2 resistor in rfc1, earlier boards could be using a different value though.

Is he building the kit ? NRG PLL PRO III .

The resistor value frequently changed according to stock levels! The value isn't too critical - it just damps the "Q" of the coil wound around it and broadens the effective bandwidth of the supply filtering.

There are a couple of useful tricks for the Pro III:

It's worth strapping the two ground pads beneath the output transistor. If you have a good heatsink on the output transistor, you'll get just over 5 Watts at 13.8 Volts instead of the usual 4 Watts.

You need to know the PLL loop control voltage at the emitter of TR1 - it needs to be centred accurately on 3.2V, and I designed a simple indicator add-on to allow easy adjustment without a multimeter:
The indicator needs to be powered from the regulated 5V rail - the supply to the logic is fine - and the input connects to the emitter of TR1. The type of dual op-amp isn't critical - I've made them with TL072, LM358 and even the 4558. You set the DIP switches for your required frequency, then slowly turn the trimmer capacitor until you get lock. Them slowly tweak to get both of the indicator LEDs off. This ensures that the control voltage is centred on 3.2V. You'll then find at switch-on, lock will be attained very quickly! The layout of the components for this indicator is not critical - I build them on a little piece of "Veroboard". I'll put the layout up here later if anyone wants it.

As promised:

download/file.php?id=885

,done before years ,there was a leaked pcb layout on the net,but the funny things i tune it with a vero 1w pll same procedure,before i done 1 nrg kit without final transistor for lack of components.i will search to see or i took a new picture of it .It took me some time to understand the function of it ,yes for zero null the 2 leds must turn of when reaching center lock frequency.