Turkish RDVV low power problem

polestar · Post by **polestar** » Sun Nov 06, 2016 8:02 pm

please control voltage regulator an error two unit rdvv
79l09 error
will 78l09 ok

MiXiN · Post by **MiXiN** » Mon Nov 07, 2016 12:19 am

polestar wrote:please control voltage regulator an error two unit rdvv
79l09 error
will 78l09 ok

There's already a 78L09 regulator fitted to mine, so are you saying replace it with a 79L09?

What will replacing this achieve?

Also, you didn't answer Analyser's question about the bias!

Albert H · Post by **Albert H** » Mon Nov 07, 2016 1:44 am

It should be a 78L09 (the 79L09 is a NEGATIVE supply regulator!)

Albert H · Post by **Albert H** » Mon Nov 07, 2016 1:55 am

The bias scheme on that Greek forum looks completely wrong, and shouldn't be coming from the variable supply (that's used to turn the power up and down). It's not trivial to vary the output power with a biased FET, as the bias required will vary with the supply voltage, but NOT in any direct proportion (it's actually closer to a square-law relationship).

The older version of this circuit allowed smooth variation of the power from about 1 Watt to about 7 Watts when you used the 2SC1971. Both the driver and the PA had their supplies varied, and because the PA was operating in Class C, the power variation worked quite well, and the spectral purity of the output wasn't significantly compromised.

I haven't tried out one of the newer RDVV boards with the FET output stage, but I really can't see how the variable power function can be made to work cleanly if the FET has any forward bias, for the reason given above. Any scheme to make the bias vary in a non-linear fashion would tend to be very temperature sensitive, and the circuitry to make this work properly would end up being more complicated than the whole of the rest of the rig!

I suppose you could vary the driver stage supply voltage to get variable power, but this presupposes that the final stage is biased to be truly linear, which really wouldn't be at all efficient, and could reduce the output stage gain.

MiXiN · Post by **MiXiN** » Mon Nov 07, 2016 5:37 pm

Albert H wrote:It should be a 78L09 (the 79L09 is a NEGATIVE supply regulator!)

Without checking the spec' this is what I thought it was.

I think we can safely say that the Turkish guy knows about as much about RF engineering as me - IE very little.

Not particularly impressed with having to spend money and faff about with this RDVV just to get it running "normal".

I'm gonna await the arrival of the 6W MOSFET & VK200 Ferrites then just read this thread from start to finish and hope for the best.

A big thank you to everyone who's helped me on this, it's really appreciated.

sinus trouble · Post by **sinus trouble** » Mon Nov 07, 2016 11:41 pm

The conclusion is that Mr Polestar has not been entirely clear on what his customers are buying!
All due respect, the PCB looks excellent quality! But designed only for a bipolar transistor output stage!
Call me fussy?? botch style FET bias is a No No for me!

Gigahertz · Post by **Gigahertz** » Tue Nov 08, 2016 2:06 pm

I also bought a RDVV off the Turkish guy. Ordered a RD06HVF1 from enigma.

Just fitted it this morning and my results from a mydel mp-30 PSU with crappy on board volt/amp meter into a Diamond SX-600 VSWR meter and dummy load.

87.5mhz - 13.8vdc it draws 0.8amps and gives 4watts.

98.0mhz - 13.8vdc it draws 1.8 amps and gives 2.2watts

108mhz - 13.8vdc it draws 1.9amps and gives 1.5watts.

If you adjust the power control pot to far it goes into saturation.

I also bought the same board but from a UK seller "who bought it from the Turkish guy" the UK seller put a 2SC1971 on it and it produced 1watt and over 10mins backed off to 0.5W

Gigahertz · Post by **Gigahertz** » Tue Nov 08, 2016 2:11 pm

And with15vdc results are pretty much the same with only a big difference of 87.5 it produces 5.5watts.

Analyser · Post by **Analyser** » Tue Nov 08, 2016 4:30 pm

Sounds like there is something seriously wrong with these boards he's sending out, none are working properly whichever final transistor is put in them. Sounds like a cock-up with a component value or PCB layout somewhere.

As myself and others have said before you should not be able to randomly drop bipolar and mosfet RF transistors in to the same circuit and hope that they both work.

I'm really not surprised that these boards are only doing a few watts at best and that performance varies a lot over frequency.

Methinks that someone who made these and saw 15-20W power out was using a 30MHz CB power meter or smoking some serious shizzle,

but hey, they're really cheap and you can learn something whilst trying to work out what the f**k is going on.

... and no kebab jokes please.

shuffy · Post by **shuffy** » Tue Nov 08, 2016 5:43 pm

Analyser wrote:Methinks that someone who made these and saw 15-20W power out was using a 30MHz CB power meter or smoking some serious shizzle,

Perhaps it's psychoactive whatever those inductors are made of!

yellowbeard · Post by **yellowbeard** » Tue Nov 08, 2016 6:44 pm

So how is the part of the transmitter that is working? You may be able to bodge the situation by building the power amplifier on a separate board from a kosher diagram and layout, but it'd only be worth it if the driver is clean quiet and stable. If in doubt, Gunther!

RF-Head · Post by **RF-Head** » Tue Nov 08, 2016 8:24 pm

8Watt.NoTune.JPG

Here is the original layout where they made a copy of
maybe change it to a 2SC1971 like on this layout
Never knew that there so many copys of my old designs on the web

Radio Garfield · Post by **Radio Garfield** » Thu Feb 02, 2017 8:49 pm

RF-Head wrote: ↑Tue Nov 08, 2016 8:24 pm 8Watt.NoTune.JPGHere is the original layout where they made a copy of
maybe change it to a 2SC1971 like on this layout
Never knew that there so many copys of my old designs on the web

Hello.

Can You explain me please what is the purpose of that series combination of resistor (680R) and electrolytic capacitor? There are just below audio level POT on board.
1k resistor, El-cap 100uF and resistor of 680R are in series and going to ground. I dont understand it really.

Albert H · Post by **Albert H** » Thu Feb 02, 2017 10:08 pm

If you think about it, the 1kΩ and 680Ω are in series. That's (effectively) 1k68. The 100µ capacitor in series with the resistor is part of the PLL loop filter. The probable reason he broke the resistor into two parts was to give him a jumper where he needed one - without using a piece of wire. It's a PCB layout trick that I've employed from time to time.

Also, resistors in series or parallel is often a cheaper way of getting an unusual value - E48 resistors cost a hell of a lot more than a couple of E12! One VCO that I use a bit demands a 9p capacitor. I can buy 9p1 parts from some suppliers (or I can select from a pile of 10p and 8p2), but it's far easier, cheaper and less time-consuming just to put two 1% 18p caps in series.

Component selection is often a case of economics!

Maximus · Post by **Maximus** » Fri Feb 03, 2017 1:25 am

RF-Head wrote:
8Watt.NoTune.JPG
Here is the original layout where they made a copy of
maybe change it to a 2SC1971 like on this layout
Never knew that there so many copys of my old designs on the web

Hi RF-Head. Maybe you can help me again dude. The last time you helped me, I accidentally fitted a 2.2uf cap to the pll of on a pkbee 15w kit, so I was barely getting a swing to lock the frequency.

Well this time I've built a newer version 8 watt notune rdvv. And there's barely anything coming out of it, and this is when the thing decides to oscillate.

Maybe you guys can help? The board layout only uses one crystal if that helps.

Sent from my iPhone using Tapatalk

Maximus · Post by **Maximus** » Fri Feb 03, 2017 1:27 am

Forgot to say I put the bfr96 in the wrong way as I was in a rush, but bought a new one to replace the original. Even though the original measured fine anyway

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Maximus · Post by **Maximus** » Fri Feb 03, 2017 1:29 am

Plus I haven't soldered the outer casing of the crystal to ground yet either. It's a fun project for the weekends to keep me out of the pubs lol

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MiXiN · Post by **MiXiN** » Fri Feb 03, 2017 9:16 am

If you bought it as a kit, check the final Transistor and other imperative parts to make sure it's not a el cheapo. If you just bought the PCB and have used/sourced your own good parts though, just ignore what I've said.

Also, is the 3.3K Resistor meant to be missing that's about 3/4 of an inch to the right away from the Varicap's?

Sorry I can't help more, but RF-HEAD will no doubt be able to guide you.

Analyser · Post by **Analyser** » Fri Feb 03, 2017 11:28 am

That 3.3k resistor looks like it's used to bias the buffer amplifier, so it's needed if you haven't fitted one already. Also, try to straighten out the turns on your coil at the top left of the board, some look like they're touching.

Radio Garfield · Post by **Radio Garfield** » Fri Feb 03, 2017 12:25 pm

Dont test it without the heat sink.

Are you sure it is the self-oscilating or maybe its out of lock? If You have freq-counter check this thing first, then tell us.

Turkish RDVV low power problem

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