Smartkit 1187 3watt VCO kit

[Prism]

Just a quick question, has anybody got the circuit diagram (with component values) of this kit please ?

[woodyalaska]

This?

https://www.smartkit.gr/media/catalog/p ... 87_1_1.jpg

[Prism]

Yes thats the one mate, l have that but I need component values.

[radium98]

@prism you need them for pll or 4 vco ? let me help , but show us what you are doing .

[Albert H]

Prism - don't do it! Really - just don't!

It's a horrible circuit with no output filter. If it's being "free-run" without a PLL, it'll drift dreadfully. It's just a Colpitts oscillator with three amplification stages after it. I presume that the final device is either a MRF237 or an SD1127. Either device will need a big heatsink, and in that circuit will produce almost as much on the harmonic frequencies as on the fundamental. The audio level meter circuit is horrible too, and won't work properly.

Why don't you get a nice kit like https://www.ebay.co.uk/itm/165133261645?

These work well, and don't drift. If you need more power, it's easy enough to build a PA stage.

I recently used one of these boards in a little project: I ran it at 12V (650mW out after an additional filter), and used that to drive a little FET PA to 25 Watts. The only mods I made were to add a passive L-C RF filter to the MPX input, and brought the pushbuttons out to a front panel, together with a key switch that turned off the buttons to prevent curious fingers changing the output frequency! I also added a little frequency counter module to the front panel:

https://www.ebay.co.uk/itm/334027577111?

The final mod was to add a supply reversal protection (for colour-blind idiots)!

It's a neat little battery powered 25 Watt rig.

[radium98]

Albert it is not the 1021 4w , i think you are wrong . how do you know it drift and bad and not good and and ... do you have one ? did you try it .i think you mistaken with the 4w 1021 , the 1187 is another pcb , and seems good .yes no filter .tell me wich exciter of 1w other the ones you may populated , has an onboard filter .Theses days any good brave guy who have a brain , can do and tune a filter .In the era there was problems because they were no instruments .Some cheap instrument are around .
he ask on the first one with his pll .The last one is very ugly and bad , drift ... harmonics and spurs .

[zulu53]

Albert,

I would appreciate if you could let us know what simple 3-5W amplifier circuit would you suggest to boosting your favorite 12V/650mW transmitter?

[MiXiN]

The Smartkit 1021 was a 15W VCO transmitter that drifted terribly, used a BLY89C transistor, and only actually gave out a few watts on the correct frequency; it was my 1st ever pirate transmitter way back in the early 90s, and they're still available now which is madness! https://www.smartkit.gr/fm-transmitter-15w-m.html

With PLL FM receivers now being the norm', the chances of one locking on to any Smartkit transmitter for more than a minute would be a miracle.

The driver that Albert mentioned is a good one, and these are also good by Reverend on here - viewtopic.php?f=12&t=2977

Please, please, just leave the crude Smartkit stuff alone; the 1980s are now gone & technology has improved drastically since then.

[Albert H]

The 1187 is truly horrible. I saw one in a nice steel instrument case, with a good quality power supply, and it was dreadful. It drifted, had spurs across the band. and more harmonic outputs than I could count. The spectrum from it looked like a hedgehog! There was nothing that could be done to make it any better.

[Albert H]

Albert,

I would appreciate if you could let us know what simple 3-5W amplifier circuit would you suggest to boosting your favorite 12V/650mW transmitter?

I'd probably go for a 2SC1971 in a simple broadband circuit, so that it wouldn't need tuning. With a 12V supply, you'd probably get around 4½ to 5 Watts for 650mW drive.

[radium98]

Smart

[Prism]

Thanks for the replies guys, it appears to be a load of trash then. Back to the drawing board for me then, Im looking at boosting a 300mw signal upto 2-4 watts and was gonna replicate the final rf stage of that circuit as it uses the BFS22A which i have here. Any simple 'add on rf amp' sudgestions ??????

[radium98]

Prism let me know what you need . do you have the vco or the ll card ? you were asking for components value , and i see you know it now bfs22 that is one listed on as i remmber

[radium98]

From over a 10 years , home made .

[teckniqs]

From over a 10 years , home made .

Very similar to the early PLL London pirate exciters from the late 80s/ early 90s

[Shedbuilt]

The Smartkit 1021 was a 15W VCO transmitter that drifted terribly, used a BLY89C transistor, and only actually gave out a few watts on the correct frequency; it was my 1st ever pirate transmitter way back in the early 90s, and they're still available now which is madness! https://www.smartkit.gr/fm-transmitter-15w-m.html

Very nasty. Amplifying an oscillator like that, never ends well. Sticking a 15W PA on it - as you said, madness. It's a horrible design on almost every level !!