Ramaey SS70C tuning??

[206]

Hey all....I got a ss70 descambler kit from Ramsey elect. and built it yesterday(man my soldering skills have faded) Felt like a kid again in electronics class.

Anyone tell me If and How I could tune this little unit?

I never realized til it arrived there is no adjustments on it?

It actually does unscramble transmitions but they still sound really hi-pitched(like they sucking helium balloons)

Any suggestions?

Thanks

 

[kb2vxa]

OK, without seeing a schematic I can't be specific so I hope this rather vague instruction helps. Locate the pilot tone oscillator and modify the R half of the RC feedback circuit by adding a Trimpot (r) and lowering the fixed value accordingly. By varying the frequency you vary the tone of the unscrambled audio just like tuning a BFO on an SSB receiver to clarify the audio. This is why it's called a "clarifyer" on an SSB CB set.

Alternately you can disable the oscillator and inject the pilot tone from an external source such as an audio generator if you have one lying around on your test bench. The tone is always near the middle of the standard 300~ to 3KHz audio range, usually between 1500 and 2500Hz.

Here's another clue for you all, the walrus is Paul. Looking through a glass onion; the unscrambler is a balanced demodulator quite similar to an SSB product detector only instead of operating at the receiver's IF it operates in the audio range.

"they still sound really hi-pitched(like they sucking helium balloons)"

Maybe they are.
"Let's GOOF on 'em!"
Wakko Warner

 

[mancow]

If adjusted properly the audio should be almost indistinguishable from normal unscrambled audio.



They may have changed the design since MX-COM went out of business (I think) but when I bought one it was based on the MX118 chip. The short answer is that mine was based on a 4.433 Mhz Mhz crystal oscillator.

The bizarre thing is that I came across my MX-COM product manual just this weekend and I'm staring at the pages for the MX118. The book says the MX118 is a full duplex scrambler for cordless telephones. The audio paths are enabled independently of each other. It features a 10th order low pass filter cut off at 3.1 kHz, balanced modulator with high baseband and carrier rejection, 3.3 kHz inversion carrier, 14th order band pass filter for (300-3000 Hz), input op-amps with adjustable gain.

It operates from a single supply from 3.0 - 5 V.

The inversion frequency and and filter switching clock are generated on-chip using and external 4.433619 MHz crystal or clock input.

So, I guess you could try some small trimmer caps at the crystal to vary it slightly or you may try other crystal frequencies. 4 MHz should be easy to find as well as a 3.579545 TV colorburst crystal.