# Band Pass Filter CF 3395.4MHz Design Help

#### W7NUK

Joined Mar 12, 2017
17

Thanks

#### BR-549

Joined Sep 22, 2013
4,938
That's 3395.4 KHz, not MHz. I would suggest restoring to original specs with the supplied options.

Then get a breadboard and start experimenting with active filter op-amps. You can put a CW filter in line with your headphones.

#### MrAl

Joined Jun 17, 2014
6,642
Hi,

I thought my eyes were going bad when i saw something around 4GHz.
I had to look and re-look at that several times
4 MHz is doable for hobby radio guys.

#### W7NUK

Joined Mar 12, 2017
17
Yea sorry about the mistyping. Everything in the manual reads as 3395.4 and I'm thinking MHz as I read it written in KHz. Two lines of thought lead me wrong. So I may have to try getting a few parts and see what I can build. I will have to undig my signal generator. Got half my stuff packed up! Wrong time to work on projects as the house is on the market.

Would be cool to build my own but seeing the parts needed makes me a little worried. Some capacitors are 0.0028pf some inductors are 0.00ish uh. Seems like stray cap/inductance of wire but if I do it as wire I think it will short everything out. Could be wrong.

Just don't know really how to start on this. Never did anything like this before! I would try a filter for headphones, if I had some. But I also don't know what frequency CW comes through the speakers as when zero beat properly. Well I guess it's about time to learn anyways. Time to experiment!

#### BR-549

Joined Sep 22, 2013
4,938

They all take normal common cheap parts.

#### MrChips

Joined Oct 2, 2009
19,415
I am not sure I understand what you are trying to do.

This is basically an adjustable oscillator close to the intermediate frequency (IF).
If the BFO frequency is exactly tuned to the IF you hear nothing. You have to shift the BFO frequency so that you will hear the difference between the BFO frequency and the IF.

Hence if you want to hear the CW as a 400Hz tone, you set the BFO to either 400Hz below or above the IF.

You can also use the BFO to recover single side-band (SSB) voice transmission.

#### BR-549

Joined Sep 22, 2013
4,938
The radio does that in cw mode. he gets the cw tone.......but with a wide noisy bandwidth.

AN active filter can center.....500....300....100 Hz around that tone. If he likes 400 hz tone...set main tuning for 400 note. I prefer 700-800 myself. So I built my filter for that.

#### W7NUK

Joined Mar 12, 2017
17
T

They all take normal common cheap parts.
Thanks for the info on that. I'm looking at it online. And don't worry. Whenever I modify my equipment I like to make them as easly reversible as possible. I highly believe in preserving vintage equipment. But why not enjoy it too? As long as it can be reversed easly I don't have a problem. So no drilling holes unless it's a simple easly replaced part.

What I thought for the filter would just be a plug in type unit in place of where the original CW filter would go with minimal mods to the radio itself. But since your idea is much easier and better. So if I could figure out how to implement it into the rig and use the original filter switch to bring it in and out that will be cool. Implement the filter inline with both the speaker and headphones would be perfect. Then either one would could use it. Might be tricky but somehow it could be done.

More research is needed but an idea is nearly there! By the end of the weekend I should know how and what I need to do with it. Then just have to learn CW! Well need to build it first

#### BR-549

Joined Sep 22, 2013
4,938

#### MrChips

Joined Oct 2, 2009
19,415
This is what worked for me in learning code.
Of course, sending is easy. Receiving is the difficult part.

Get yourself a practice key and oscillator.
Record yourself on a tape recorder (if they still exist). Start off with random T, E, then add A, I, M, N.
When you have mastered receiving those, move on to random D, G, K, O, R, S, U, W mixed in with the previous set.

Finally, add the remaining longer letters and numerals.