FREQUENCY SHIFT CONTROL

[daverave]

How much frequency shift should there be to help reject interference on a pulse detector using the 555 timer as the oscillator...for say searching on a beach !!! will say a 1k or 2k potentiometer give enough frequency shift ???

[FschJg]

About what machine are you talking?

[daverave]

ive now edited my question.

[kt315]

your choice for bara & surf

2*50 100Hz
4*50 200Hz best pitch for hearing
6*50 300Hz
8*50 400Hz
10*50 500
12*50 600 optimal, but bad pitch ie hight. range of bara and surf frequency.
14*50 no sence, too hight pitch

[daverave]

i want to add an external frequency control to my detector to tune out interference...if say my tx frequency is 3 khz then how much shift would i need like what value potentiometer would i require like 1k...2k..5k so i can frequency shift either side of the 3 khz tx frequency.

[kt315]

seems you do not know what is interferency. what range of shift you want get?
0.1hz? 1hz? 10hz? 100hz? 1000hz?

[daverave]

when im on the beach i get interference from amusement arcades and other detectors if close to me so i want to try and minimise the interference with a control but not sure how much of shift either side of 3 khz that is required...maybe + or - ...250 hz either side of 3 khz ????

[dfbowers]

I have been using a PI designed by Cyril B. Smith named the Manta (similar to Svens Mirage) where he implemented a dual gain front end for faster sampling and a frequency control of 1800 Hz with a 10% adjustment range. I find it to be highly effective at eliminating EMI. Even inside the house I can eliminate almost all noise with careful adjusting. I thought about adding this feature to some of my other PI projects as well.
Don.

[Dave J.]

In general, a shift of +/- 100 Hz is more than enough. When that doesn't do it, the interference is usually broadband and frequency shifting is no help.

[daverave]

ok thanks to you guys for your help much appriciated

[surfdetector]

I have been using a PI designed by Cyril B. Smith named the Manta (similar to Svens Mirage) where he implemented a dual gain front end for faster sampling and a frequency control of 1800 Hz with a 10% adjustment range. I find it to be highly effective at eliminating EMI. Even inside the house I can eliminate almost all noise with careful adjusting. I thought about adding this feature to some of my other PI projects as well.
Don.

Hi Don,
Is this a detector that is available?