HH Opt.1 (Vco) vs. Opt.2 (non Vco)

[Stefano]

Hi all.
I've just changed my Opt.1 Vco version of HH (version B3 pcb) to opt.2 non Vco including the last changes of the C version pcb, because I found a bit annoying the click sound level in the earphones.
Now the audio is probably more suitable for a long search since the threshold level can be set very low, but I noticed a decrement in sensitivity.

What I didn't expect is also that the pitch changes by changing the pulse width. Is that normal? Could it be avoided ?

It would be very interesting in my opinion, have an audio signal with both amplitude and frequency increments. May be I like this form of audio because I own a Minelab Sov. so I'm used to it, but I think targets would be more easily recognized and ears woudn't suffer when no target is present. Do you think such modification would be possible for the HH?

Thanks
Happy New Year

Stefano - Italy

[Carl-NC]

Yes, in standard (non-VCO) audio, the audio frequency is the same as the pulse rate. This option was an afterthought, and had I given it a little bit of effort, I could used the VCO 555 chip to generate an independent audio.

However, the audio pulses can interfere with the signal sampling, and one of the reasons for using the main clock for the audio, is to make the interference coherent and somewhat controllable. So keeping the audio on the main clock is best.

I had not noticed a decrease in sensitivity using the standard audio, but I really have never used it much... just enough to test it out. I agree, a more flexible audio would be nice, and would be fairly easy to do, possibly without much change to the existing design.

- Carl

[Stefano]

I agree, a more flexible audio would be nice, and would be fairly easy to do, possibly without much change to the existing design.
- Carl

Thanks for answering Carl.
Well, I hope to see the electrical drawing of this simple modification in the forum in a near future...

Again, Happy New Year !

Stefano