Which transmitter?

[rickylee]

I've been trying to build a usable crystal controlled "bug" a few times but have always failed miserably Now I'm going to give it another go, but it would obviously be a good thing to know whether the circuits would work in the first place , and if they should but won't, then where will I have <snip> up... I've found four circuits so far, have been unsuccessful at building the first two, and would really appreciate it if someone could take a look at these (where'd I mess up?), and also the other two (as in would they work, there's no PCB drawings and laying out my own is a real *****...)

1: The Talking Electronics "Crystal locked bug" Crystal Locked FM Bug. Made two versions of it (TTH and SMD on my own PCB's since the original is just too damn big), the RF part was essentially same as the original (with the exception of a resistor instead of inductor in final amp/buffer stage), the audio stage was replaced with an LM386 in 200 gain mode. Couldn't get the SMD variety to work at all (might be my awzum sold3r1ng skillz...), the TTH did oscillate but didn't have any modulation (neither WB nor NB) though the 386 front end worked properly when connected to another, free-oscillating transmitter.

2: This one https://www.electro-tech-online.com/attachments/sp_18-jpg.42599/. Replaced the FET with a BF245C and tried a bunch of assorted varicaps and signal diodes for the SK3126 (no datasheet to be found for it anywhere), couldn't get it to work.

3: This: **broken link removed** Nothing really about it except "would it work", will probably also have to replace those "1 to 100pf or whatever" trimmers with smaller ones + fixed caps etc...

4: and this: **broken link removed**. Same question as above, also, should there be some sort of a trimming device in the first osc stage?

 

[rickylee]

Crap, couldn't get the attachments to work and the "edit post" function doesn't have the "attach" button... Try #2:

 

[rickylee]

Not much interest in RF stuff here I guess... Will try building the first two again, IF I'll get them to work I'll post it here...

 

[jim digriz]

I was very interested when I saw the schematics for the "Bugging Transmitter" that operates on the POLICE LO BAND. I now have a copy of that book--which is pretty rare. The varactor (SK3126) is an old Phillips model and after some research I found it can be replaced with a MV2109. The book doesn't specify the final frequency, but since it's a VHF LOW BAND (30-50MHz), I presumed that 48MHz--the 3x multiplication for the crystal--would work for the tank circuits. Substituting a 15MHz crystal would put the final freq at 45MHz. And, in fact, the coil as designed would operate well in this range when I checked it with a dip meter. I made them a smaller size by winding on a 3/8" nylon washer with 26ga magnet wire. I etched the board and soldered it all in--it works very nicely. No range checks yet.
Pete
KEØBRS

 

[dr pepper]

Welcome Jim.
Nice pcb.
Didnt sound like the o/p was well into Rf, and I dont think they'll be back, that was 7 years ago.
Operating at a harmonic requires a little tweaking expertise, from my experiences.
I know you replied to a thread, however you'll get better responses from the radio/comms section of this site for this kind of stuff.
Doesnt sound like your in the Uk.

Aside: I've been frequenting this forum since 2008, and rickylee is the first poster I've noticed using profanities, the mods here seem to be sensible.

 

[jim digriz]

Thank you Dr. Pepper. I am not in the UK--but in the USA. I'll post my radio things to the proper section also. In this project, I had to make sure the tank circuit--the coil and variable capacitor combination--resonated at 48MHz. That took a bit of experimenting, but was easy enough to determine. I wound the original as per the instructions, then had to wind other coils around a nylon washer until the values were similar. The variable capacitors range from 9-50MHz. This circuit was originally published in 1979 in a mail-order pamphlet entitled "A portfolio of electronic surveillance devices" but had no author attributed.

 

[DerStrom8]

Aside: I've been frequenting this forum since 2008, and rickylee is the first poster I've noticed using profanities, the mods here seem to be sensible.

Edited.

 

[dr pepper]

Derstrom, thanks for that.

Jim, I'll remember the nylon washer tip, I've routed round for non magnetic stuff a couple of times for that job.

 

[DerStrom8]

Derstrom, thanks for that.

Thanks for pointing it out. I wonder how it slipped through the censors....