NRG 40W PLL

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piraterx
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NRG 40W PLL

Post by piraterx » Fri Dec 21, 2018 3:14 pm

Hi all

A friend of mine recently got himself a second hand pro3 40W NRG PLL built by the great Mr Moss many years ago(i was a fan and reg user of nrg gear many moons ago).

He says he switched the 40w tx on and set the freq via the dip switches,then adjust VC1 on the drive board to have it PLL locked.So red UNLOCK light starts dimming and GREEN LOCKED light comes on.-all good.

Next and this is where the issue is,he says the RF POWER Light and indeed the RF Power itself takes some 5seconds or more before it powers up,ie as tho there is quite a lag or delay in the RF Power coming on.Even once fully powered up and tuned,if he switches it off,leaves it a bit then switches it back on,the unit locks reasonably quick and well but he still has some time before the RF power comes in.

Any ideas on whats causing this?

Other 40W NRG PLL transmitters are generally quite quick from PLL Locking to RF Power coming on.Maybe the 40W he has is just an old soul in need of TLC.

Albert H
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Re: NRG 40W PLL

Post by Albert H » Fri Dec 21, 2018 8:13 pm

The delay is meant to be around 4 seconds. There's nothing wrong with the rig - it was just to ensure that nothing reached the aerial until the PLL has locked for a couple of seconds, to make sure that nothing was transmitted on a "wrong" frequency.

You might find this useful, as it guarantees that the trimmer capacitor in the VCO is set correctly for fastest lock-up:
Tuning_Indicator_tidied-V2.png
You can build it on a piece of strip-board or with any other type of construction you favour. The emitter voltage for transistor TR1 should be 3.2V at optimum. You slowly turn the trimmer with a non-metallic tool until both LEDs go out. You're them set for fastest lock-up and quietest carrier.
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sinus trouble
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Re: NRG 40W PLL

Post by sinus trouble » Sat Dec 22, 2018 9:08 pm

Totally agree with Mr Albert, Sounds normal to me!

PLLs wont usually jump instantly to a set tuning voltage, They generally track slowly and smoothly towards frequency it is looking for!

So the closer the initial startup frequency is to your required lock frequency, The less tracking it will need to do!
If that makes sense?
I am as stupid as I look! :|

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Re: NRG 40W PLL

Post by Albert H » Sun Dec 23, 2018 5:18 am

Exactly right, Sinus! That's why the indicator circuit I gave above was going to be added to the next version of the NRG PLL Pro exciter. It allowed the user to get the VCO adjustment exactly right, which gave fastest lock and lowest carrier noise and modulation distortion. It runs from the 5V regulated rail that feeds the logic ICs, and derives an accurate 3.2V with a potential divider. The first op-amp just amplifies the voltage from the emitter of TR1 and the second op-amp compares it with the 3.2V reference, displaying the result on a pair of LEDs.

There's also another version of this circuit that replaces the LEDs with a pair of H11F3 opto-FETs, and clamps the incoming modulation when peak deviation is reached! I'll leave it as an exercise for the class to see if they can work out how to do this. My circuit was set up to drive the pair of LEDs in "tune" mode and then you moved two jumpers, and it became the deviation limiter!
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Re: NRG 40W PLL

Post by radium98 » Sun Dec 23, 2018 6:53 am


Albert H
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Re: NRG 40W PLL

Post by Albert H » Mon Dec 24, 2018 2:32 am

That's neat!
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piraterx
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Re: NRG 40W PLL

Post by piraterx » Sat Dec 29, 2018 11:00 pm

hi guys thanks for the replies.

I appreciate the pll will slowly lock and tune up but according to my friend it seems like it takes pretty long to tune up after it locks (locks which it does quickly).I havent had time to visit him yet but i did ask what psu he got and his reply was 3-5A. From my memory i am sure they need 7-9A or more for the 40w pll? I did recommend this to him but dont think he was listening! Could this be anything to do with a slow rf output appearing? I know you experienced guys said its normal but he did send me a vid of it and it is quite slow,in fact more than 4 seconds.I remember having used a 40w pll when NRG started selling them and mine always locked and powered up pretty quickly.

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Re: NRG 40W PLL

Post by sinus trouble » Sun Dec 30, 2018 1:04 am

Hello again Mr RX
Im guessing your friend tuned it himself and has no experience in electronics?
That is the main problem!
With regards to the PSU, I would say 5A minimum! An easy diagnosis would be a slump in voltage once the amp tries to power up!
The PLL also needs to see a 50ohm load on its output to lock correctly, I suggest you disconnect the amplifier and stick on a dummy load!
Once the PLL is working alone, You can then reconnect and tune the amplifier for optimal settings!
I am as stupid as I look! :|

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Re: NRG 40W PLL

Post by Albert H » Sun Dec 30, 2018 4:24 am

Do the mathematics!

The 40W PA will be (roughly) 50% efficient at best, so you need to provide (at least) 80 Watts of DC power. The supply voltage is probably 13.8 Volts, so the current required will be a minimum of 80 / 13.8 = 5.8 Amps. Bear in mind that you have to power the exciter as well (roughly another Amp), and you're looking at a 7 Amp PSU.

The PSU circuit that Stephen used inside the mains powered 40 Watt rigs was capable of about 10 Amps. The mains transformer was rated at 12V secondary at 120VA (a standard toroidal transformer size). Rectified and smoothed it gave about 16.2V DC, which fed my regulator circuit - the earlier ones were based on the 723 regulator IC, and later ones used a LM317, with two 2N3055s as the series-pass transistors in each circuit.
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