View Full Version : mobile bug

10-03-2010, 06:37 PM
i want to make mobile bug

i found these lines which i am unable to understand ::

""The lead length of the disk capacitor is fixed as 18 mm with a spacing of 8 mm between the leads to get the desired frequency. ""

you may check at

is these lines convey , that we have to adjust the spacing & lead length of capacitor
HEY , i want to know is there any capacitor whose spacing & lead length can we adjusted

if am wrong please me out.

10-03-2010, 08:55 PM
lead length : means length of metalic wire attached to capacitor itself.
8 mm between the leads : means these wire should solder on board contacts with drill hole 8mm apart.

10-04-2010, 08:32 AM
thanks for your help

i want to know
if we use a capacitor with 8mm ,4mm etc apart in board, is this make any difference in capacitor behavior

what the use of drill them 8mm apart , as spacing of a capacitor is constant which is made during manufacturing
then how can we change spacing

10-08-2010, 01:01 PM
The .22 disc ceramic capacitor is used as a LC tuned circuit; with the leg lengths of 18mm spaced 8mm spacing and stray capacitance , it will act as a high gain tuned circuit at the Mobile phone transmitting frequency ( 900MHz - 3Ghz ).
A 1nH inductor and a 1pf Capacitance will resonate at 3.55GHz. It will produce more Voltage (& current) at this frequency and may shunt or choke voltages @ other frequencies.

The original authors' explanation of this ' acting like an antenna' is not correct as I see it. The antenna as such , is the part that extends from the top most part from C1 the 22pf Capacitor.
any change in the given dimensions will detune the LC ratio and hence the Resonant frequency . This will lead to the circuits failure as it may 'ground' the signal instead of enhancing it.

10-10-2010, 12:42 PM

You can buy the kit here.

10-10-2010, 01:18 PM

You can buy the kit here.

This guy is trying to MAKE it himself, for a change ......
What good is a Ready-made link ?? It may discourage self learning and enterprise..... a foundation for the likes of Diwaker Vyas ;);)

10-10-2010, 02:00 PM
The kit will just provide him with components and circuit print out.He still has to make it himself.I know he'll learn more even in the process of finding components but i don't want him to leave this project just because of small component or doubt.The kit will atleast solve his capacitor problem :) :)

10-13-2010, 09:36 PM
i understood, all concept you guys explained

but i have still a doubt

i want to know that, we have to use normal ceramic capacitor whose leg length is 18mm,and have to drill in pcb at 8mm apart

10-14-2010, 08:21 AM
Youre right. Make sure the Capacitor is vertical.