[HELP]Simple Surveillance Transmitter (VARICAP) Schematic +

[Nina]

varicap circuit

Looking for a Simple Surveillance Transmitter (VARICAP !!!) Schematic.
About 110 -130 MHz, as small as possible... Need this plan very badly !!!
Another related problem I have: I'm trying to build a "mains" operated xmitter.
Using a transformerless PS ( a serial capacitor + diode bridge + filter capacitor) gives me very much humming, even a stab. doesn't solve this problem.
I know that such device is been sold over the net, and I'm curious how they solve this humming problem or your idea.
I'll be very thankful for your help.
TIA
Nina

 

[papyaki]

varicap

Hi,

Some good schematics here :

h**p://members.tripod.com/~transmitters/links.htm (scroll down the page).

Replace * by t

 

[Nina]

simple transmiter schematic

Thanks papyaki, I've visited this site today (found at Google) - but...
Many links are 404, or very old....
I couldn't find there any varicap transmitter schematics, nor any mains powered device ....
Maybe I've missed it...
Thanx a lot anyway
Nina

 

[throwaway18]

varicap schematic

110-130MHz is an aircraft band. Transmitting there could get you into a lot of trouble.

 

[Nina]

china am transmitter schematics

You are right, but I think there is not a real problem, as such devices are:
A: very low power, about 100 - 300m (a few miliWatts)
B: the Airband uses AM, so the interface may be only at subcarrier - if at all...
C: most of the Airband uses 120 -123MHz, so if having not nany harmonics, NP.
D: most of the places that uses such products are far away from airports, usually
in private buildings.

More serious devices uses 800 - 900MHz, 2.4GHz and other higher freqs, that are used on domestic appliances or cell phones... and usually more powerful....

Regards,
Nina

 

[Borber]

schematic veronica pll

Here are few schematics with battery supply:

 

[Nina]

surveillance electronic schematics pcb free

Thanx a lot Borber for the circuits.
I think that now I'm understanding the principle of "varicap controlled frequency" oscilator, and after making some changes, as a decent audio amplifier stage and one more stage of RF amplifier to encrease the gain and stability, I may use those schematics for my needs.

Regards,
Nina

Sill need any ideas for mains (220v) powered devices, humm - free, and without using a transformer PS

 

[papyaki]

varicap fm transmitter

Hi,

h**p://web.telia.com/~u85920178/

Select "Projects" then "Transmitters circuits"

h**p://www.frn.net/tech/xmitters/fm/3%20watt%20transmitter/3watt.html

h**p://www.geocities.com/Area51/Nebula/3736/veronica.htm

h**p://www.pcs-electronics.com/schematics/2wsimple.gif

h**p://www.pcs-electronics.com/schematics/fmxmit.pdf

A lot of these schematics are designed for the FM band, but with some little adaptation, it can work up to 130MHz

Replace * by t

 

[Buriedcode]

simple 300 m fm transmitter (9v) of working

Hi, transformerless power supply eh?

In 3 seconds, using google, I found:

http://www.zen22142.zen.co.uk/Circuits/Power/tps.htm
http://www.aaroncake.net/circuits/supply5.htm
http://www.discovercircuits.com/PDF-FILES/offline5v.pdf

last one (http://www.discovercircuits.com) is great. Check out 'power uspply circuits', its got loads of non-isolated PSU schems. But be warned. Transformers provide isolation. Even with fuses, Zener doides etc.. without a transformer, its a little more dangerous. You might want to 'pot' all the PSU electronics in Wax for insulation. And I've seens some pretty small mains transformers, for <200ma. About 1" cube.

For reduced hum, add more filter capacitors. 1000uF? 47uF? 1uF and 0.1uF, I'd like to see any transients bypass that lot

My two cents.

BuriedCode.

 

[Nina]

airband radio schematic

Dear friends,
I'd like to explain you my need of such circuits:
I'm retired for 6 month, working as an engineer at a telecom company at a repairing measurements stuff lab (optical and analog reflectometers etc.). In my spare time, about 15y ago I had own a personal "bug" lab, sold a few devices - but they haven't made me rich...LOL. I'm now trying to make a new one, more for fun than for profit ... I know I can buy such devices from China, "professional look" - and very cheap, but I prefer to build them, as I have a lot of free time...

@papyaki,
I'd like to thank you very much for the links. I've done a little "research" at google too and found about the same circuits. All of them really work, but they are very unstable, meaning an antena touch or even if the battery voltage drops 0.2 volts, the frequency is changing (2-4MHz)... so our "detective" must change its receiver frequency all the time.... The range is about 50-70m with full 70cm ant.

@Buriedcode
Thanx a lot for the circuits. Yes, those circuits I have had on my mind.
I've tried to use a long time ago the simplest one, better filtered annd added even a regulator (h**p://www.aaroncake.net/circuits/supply5.htm), but the humming was very high. I'll try the others too, maybe I'll have luck. I really don't know how the comercial devices are made....they have no humming at all. The wierd thing is that even after connecting my bugs - any of them - to my Very stabile LAB PSU, I still get a lot of humming, and I even cannot "catch it" on my scope... The problem occurred ONLY with any antena, without it I had almost no humming, but getting a very short range.
They work prfect with batteries (from 1.5-9V).

Thanx a lot to all of you, and if you may want to help me further, please send me more links, I'll be very thankful

Regards,
Nina

 

[Buriedcode]

www.pcs-electronics.com/schematics/2wsimple.gif

Nina,

This probaly won't be any help, but back when I was in school, I built a small bug that could fit in a match box. It was one of those 88-108MHz things, with a range of about 200m. Here in the UK thats very illegal but I was 12, I didn't care.

Anyway, looking back, it appeared to be very stable. I used to have the antenna coiled up in my pocket, walk around with it, and I got perfect reception with a pocket radio (recorded on tape), with the battery voltage from 9v down to about 6.5.

I don't know WHY it was so stable, it was a basic FM oscillator, with a transistor and an inductor, so battery voltage deffinately should have changed its frequency. The only time it ever cut out was when I put it in my dads car before he went to work (about 15 miles away).

So, my point really is, try and find this circuit! There are many similar ones (usually with an electret microhpone) but many have been simplified even more. Like using a ready-made inductor, instead of a small homemade coil (8 turns).

If you're not worried about expense, you could try a small PLL circuit, with a XTAL and chip. They're tiny these days, and can't be pulled of centre frequency easily.
I'm planning on making one, just to see if it works. I'm aiming for 1" square PCB size.

Anyway, hope that is at least 'some' help. Wish I had the schem for it, I could build it with SMD, and it would be tiny.

BuriedCode.

 

[seadolphine2000]

2.4ghz transmitter schematics

I don't know if this could help or not, it's a TX at 87.7 MHz, it's very stable and I think small modifications concerning the coil, will give you the required freq.
**broken link removed**