Opinions on another driver?

[teckniqs]

Enigma is selling genuine 2n4427 for 99p each.

[MiXiN]

Yes, http://www.enigma-shop.com/index.php?op ... e=rd15hvf1

Aha, I missed those.
Will be throwing another order his way soon so will add one to the basket.

[MiXiN]

Enigma is selling genuine 2n4427 for 99p each.

According to the webshop he's out of inventory on the standard TO5 case 2n4427, and the only ones I see stocked are the SMT version.

[teckniqs]

Ahh OK, I've got some of those tiny ones but they are MRF4427.

[shorty]

He's relisted this driver now as 80 to 90mw, not 500mw as before.

http://www.ebay.co.uk/itm/FM-BROADCAST- ... Sw~bFWMRJ1

[radio-berlin]

He has also listed a rdvv exciter which has a 2sc1971 final as a 1 watr exciter?? It's the 7 watt design but listed as 1watt.
Personally I'd stay very clear of this gear. The you tube video rings alarm bells where he is seriously over modulating an rds unit out of sync with a crap stereo encoder.. This is why pirate radio gets a bad name

[Analyser]

The money he's charging for this stuff is so low it's worth a punt just for giggles but really you get what you pay for. It's quite clear he's just regurgitating circuits he's found on the interwebs without any knowledge of RF, that's why all the specs have suddenly changed after a few boards were sent to people with adeqaute means to see what's really coming out of them.
I still might buy one of the 100mW drivers though, just to have a look at.

[teckniqs]

The final is just a 2sc2055, I changed it for a 2sc2538 and it's now doing 400mW. I expect if you stuck a 2n4427 in it then the power should be around 1w. Haven't checked it on the analyser, yet!
Yes definitely worth a punt at the price, unfortunately those PLL boards don't work without the screen attached.

....I bought one of those "1 watt" RDVV's, I asked him why it's only doing a watt when it's an eight watt board with a 1971 and his reply was this is the 1 watt version. I couldn't be bothered to tell him it isn't and just left it there. Still haven't even tested it yet, might not even do 1mW.

[koopa]

Any test reports back on this little driver board how good is the spectral purity and audio

[MiXiN]

I just got hold of the 1W RDVV from the Turkish Guy.

Mine does just over 2W at full power from around 93 to 108 Mhz, and starts slowly dropping off from around 93 to 87.5 Mhz.

Even if I drop the output power to around 1W with the power control VR, the final (2sc1971) is far too hot to touch - even with a clip on heatsink.

Can anyone suggest any fix as this can't be right at such a low power?

It's been said that he copies original designs and adds his touch of magic, so can any see how I can alter this to its original RDVV design - whichever it may be?

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[RF-Head]

For what i can see it's my original design
Only there is missing the resistor (22e)to ground with a ferritebead on it and leef the 100E resistor of this was made as a experiment to fit a RD06HVF1 in it
This is maybe also the problem why you get only 2 watt power
Also the 2SC1971 need to be grounded to the case to get it cooled

[RF-Head]

And change the Ferritebead on the collector of the 2SC1971 for a 1UH coil and also on the BFR96s

[MiXiN]

Hi RF-Head,

Thanks for the reply and helping me.

So, to summarise; I should remove the 100R Resistor on the base of the 2SC1971, then fit the missing 22R Resistor and put a small ferrite bead on it?

Could I get away with leaving the Ferrite bead links on the Collector of the 2SC1971 and BFR96, or is it "essential" to swap them with those Resistor type looking 1uH chokes?

[RF-Head]

Yes remove the 100E resistor and place the other one to ground
There is a empty place for a resistor(22E) with a ferrite bead on the legs
Yes to get full power and a cooler 2SC1971 use the 1UH coils

[MiXiN]

Thanks a lot, RF-Head. You're a star.

I'll get myself the components, fit them, and tell you how I get on with it.

[Albert H]

I just noticed on the "Enigma" site that he has a 1W Mitsubishi FET. This needs about 8V supply and 30mW in for the Watt out.... This looks like it could make for the simplest exciter ever - a VCO feeding a single stage amplifier! With a SMD PIC and an SMD PLL IC, we could probably get a 1W PLL board into 1½" × 1". I now need to find a cheap source of DG FETs and these FETs, and get a thousand PCBs knocked together in Shenzhen for about 50p each!

[shuffy]

I'm assuming your compelling reason for using this FET is the supply voltage? I've been using the MRF4427 on my driver boards now for a couple of years, with a SMD PIC and SMD MC145170. This BJT needs less than your 30mW for a Watt out at 12 - 15V. I don't like "on frequency" designs so the coils in my doubler make it bigger but it's 9cm by 4. I'm not trying to make things smaller, that's just how big it turned out. I reckon without the doubler I could do 7x4.

[MiXiN]

I'm assuming your compelling reason for using this FET is the supply voltage? I've been using the MRF4427 on my driver boards now for a couple of years, with a SMD PIC and SMD MC145170. This BJT needs less than your 30mW for a Watt out at 12 - 15V. I don't like "on frequency" designs so the coils in my doubler make it bigger but it's 9cm by 4. I'm not trying to make things smaller, that's just how big it turned out. I reckon without the doubler I could do 7x4.

Do you sell your drivers to the general public, or are they just for your own use mate?

[Albert H]

Shuffy

I always used doubler (even tripler) based exciters for the longest time. It was easy to prevent RF feedback problems from the PA to the VCO, and it was also easy to get cheap 74HC CMOS to work at 54 MHz.

My usual PLL was a 74HC4060 for the crystal oscillator and reference divider, using diode programming to get the division ratio I wanted, a 74HC4040 for the presettable divider from the VCO - again diode programmed - and a 74HC4046 for the phase comparator and the first stage of the loop filter. There was a dual op-amp used for the rest of the loop filter, and an output from the 4060 was used to drive a voltage multiplier to give ~36V. The 36V was regulated down to 30V and used for the VCO control voltage, to bias the modulation diode, and to power the loop filter. This meant that the modulation sensitivity could be at 1.5V p-p for 75 kHz, reducing the problems inherent with the typical high modulation sensitivity.

The circuit was carefully dimensioned so that the modulation sensitivity remained the same all the way across the band. Nobody else achieved this except Bext (who I designed for....).

The VCO was a dual-gate FET Colpitts derivative, chosen for its inherent purity and low phase noise. It was followed by an un-tuned bipolar buffer stage which had almost equal emitter and collector resistors. The RF for the doubler came from the collector, and the emitter signal went into the PLL.

The doubler was initially a Class C transistor amplifier with the collector load tuned to twice the oscillator frequency. Whilst this worked, it wasn't very pure and required re-tuning if the frequency was to be changed. I did do versions with a double-tuned doubler, but this only won about 8 dB improvement.

The next iteration used a Class C stage driving a diode doubler. This didn't need tuning, but lost a lot of signal because it was inefficient. The last version I did used a pair of grounded-base BF199s as the doubler feeding a passive bandpass filter. This was followed by two broadband stages and a lowpass filter, and the thing gave a Watt at 12V on any frequency from about 80MHz to 115MHz without any tweaking.

The spectral purity of these things was remarkably good, and quite a lot of them are still in service around the world. The ½f breakthrough was -87dBc, and the 1½f was -85dBc. 2f was -82dBc and I never found any higher harmonic products.

One of these boards was used for the very first legitimate site RSL at Glastonbury, and as a standalone 1W transmitter, the performance is exemplary. The only minor annoyances are the diodes that have to be soldered on to programme the required frequency. One advantage of this kind of PLL is that you can use whatever crystal is cheap at the moment - 2MHz, 4MHz, 6.4MHz, 5MHz, 6MHz, 10MHz, and even 12MHz. Another advantage is that thieves are seldom smart enough to be able to change the frequency of the rig!

I stopped using doubler exciters when I started doing commercial product design. The brief for the exciter said that it was to have no adjustments at all - it was to leave the assembly line ready to be powered. This precluded the use of adjustable tuned circuits at all, so I began by using a coiled length of RG178 coax as the oscillator resonator, and etched as many of the other inductances as possible. I had to take into account the typically 5% spread in component values - they didn't want me to use higher tolerance if possible, and I remember hand-assembling two "worst case" boards - one with all the components 5% low and the other with all the parts 5% high. Both performed within the specifications (just!).

In a commercial rig, screening and feed-through capacitors are the norm, so RF feedback wasn't ever a problem. I was also allowed to use sophisticated PLL circuits with reference-cancelling filters and multiple response speeds (to allow quick lock-up, but without compromising the bass end of the modulation). Funnily enough though, some of the methods and means that I'd used to squeeze performance out of inappropriate RF devices in the pirate world allowed me to achieve spectacular efficiency when using expensive, made for VHF devices!

[shuffy]

Do you sell your drivers to the general public, or are they just for your own use mate?

Mixin, you must have more drivers than Finglands.

Neither, really. I make them individually and the way they're set up is specific to the need. The PLL controller chip, for example, is programmed and then soldered in place, so it's hellish difficult to change frequency. This is to keep the expense down. There's no LCDs, no DIP switches, no diodes or solder bridges, just an 8 pin SMD device. I know it might not sound flexible but for a station using one frequency, it doesn't need to be! Also you need an analyser to set the doubler up properly. There are none of these in the wild that didn't start life in the TX they were designed to go in.

If I was going to design something anyone could use to make a rig by mixing and matching components, I'd probably end up with a broadband on frequency design and I'd need to redesign the PLL controller. Actually I do have some part written code intended to use the same 8 pin PIC and PLL but allowing the frequency to be set using a button and an LED. Other stuff's getting in the way of finishing it though...