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Scratchy, tiny sounding receive on SSB

Galaxyflyer1

Member
Mar 4, 2019
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For the lack of better words, that's what my Washington and 142gtl sound like. Both radios have been recapped and aligned. They perform very well and have great sensitivity. However, the receive has a very high treble with signals sounding a bit crackly, especially on the stronger signals. Even a decent external speaker doesn't help a whole lot.
So what can this be? The I.F., band pass, crystal filter? Or is it just the nature of the beast? I
Thanks!
 

The frequencies of the LSB/USB/AM carrier injection may not be properly
positioned on the slope of the I.F. filter. This can affect both the receive and transmit
audio response to a great degree. Telltale signs of this are not having the same audio
response on USB and LSB, and reduced CW power output when using the CW filter.
It is relatively easy to tell if the USB/LSB carrier insertion points aren’t placed
equidistant from the center of the I.F. filter passband. After the rig reaches a stable
operating temperature (1/2 hour) disconnect any antenna and peak for
maximum receiver gain. Next turn up the volume control to a slightly higher than normal level and listen closely to the hiss coming from the speaker. Then switch to the opposite sideband. The pitch of the receiver background noise should be the same if the USB & LSB carriers are both placed equidistant from the filter center frequency.

If the carrier oscillator frequency is placed too far from the filter passband, the receive
and transmit signals will lack “lows” but the opposite sideband rejection will be high. If
the carrier oscillator frequency is placed too close to the filter center frequency, the
receive and transmit signals will have excessive “lows” and the opposite sideband
rejection and carrier suppression will suffer. Balance is the key.

The "frequencies" given in the service manual assume that the the crystal filter has "nominal" specifications. I have never known this to be true in a 30 year old radio :)
 
@Handy Andy had a graph of this some years ago (may have been the other forum. )
Picture worth a thousand words as it were.

Your problem with the 2K sounds like incorrect mic jack wiring rather than carrier insertion points.

Again , simple test. Turn the audio up on a dead frequency (or antenna disconnected) and switch between USB and LSB . If the static changes pitch between the two something is not right.
 
@Handy Andy had a graph of this some years ago (may have been the other forum. )

Wizardsearching.jpg

Picture worth a thousand words as it were.

Your problem with the 2K sounds like incorrect mic jack wiring rather than carrier insertion points.

Again , simple test. Turn the audio up on a dead frequency (or antenna disconnected) and switch between USB and LSB . If the static changes pitch between the two something is not right.

You mean this one?
USBLSBAMPRimer.png
You may also have another condition...

High-frequency rolloff issues - @Robalo - had found a Hi-Frequency Cut filter some time ago...

But, that's for ALL audio - you seem to have more of a CENTERING issue around the IF versus BFO detect being sent to convert directly into Audio.

If you use a 148/Grant XL or even a 142 type chassis - L13 and L14 versus the 7.8MHz BASE detected off of L14 COMPARED TO X1 - X1? It's your 7.3450MHz onboard fixed reference to decode what exists off the differences between it and the 7.8MHz (455kHz) (AM) Somewhere between the L13 and L14 -(In SSB) your 7.8 BASE reference and your IF reference (from X4) - it may be why you seem to have high - frequency "Shrill" sounding audio.

Since you can't re-tune X1 unless you replace it - not recommended - you Retune L50, L22 and L23 to re-center the PLL's references - this skips the Audio side to make your radio tune BFO directly into the midrange - but in doing so, you have to retune CT2 L30 and L31 side also - just to bring the Shrill sound of the SSB modes - into the more Alto or Midrange you'd expect to hear.

You can always place a 0.01uF (103) Disc cap one on the hot side, and ACROSS to Shield can ground somewhere along the way (these radios have a Hi/Lo Tone switch for this) the Audio Out line to the Volume control and if they "Tuned" using the Lo side of the TONE switch - they overdid the tune.

PC122VCOOverlay.png
In a PC 122 you can do a similar trick to "average out" the Hiss in-between modes. But that requires you to know how and what references to use...
  • Lower Side Band - referring to LOWER side of the Channel center frequency - you SLOW DOWN PLL Side and SPEED UP the Audio side (The one that goes to the AN612 or Deconversion IF)
  • This shifts Audio Passband to BASS region
So that means the IF Frequency Counter may show LOWER than expected - which to me is why I'd just rather run the CLARIFIER and do all the AUDIO adjustments and leave the Frequency counter off - just focus on the QSO
  • Upper Side Band = referring to HIGHER than the center of the Channel Frequency - YOU SPEED UP PLL side and SLOW DOWN the Audio side of the IF to obtain those lower BASS tones. The AN612 and Deconversion IF sections respond accordingly.
  • This is shifting the Passband - again, to LOWER BASS tones.
Why does this work this way?
Because of the issue of the Beat Frequency Oscillations - your BFO., Clarifier, Voice Lock - That Galaxy KNOB that says COARSE and FINE.

Heterodyne.gif

Look up Heterodyne and understand the concepts of mixing two frequencies to make a third - derived from the difference between the other two.

Then the SSB centering will come easier and you're less likely to say - you're 1kHz off the rest of us.

You just tune to it and once set - forget it and just chat...Just like Dobie Gray, and Drift away...
 
Thanks Kop & Andy , Let's put it this way , some I understand some ..... ? This Is why I bookmarked Andy's Response , printed it out & I will let my Ham Buddy more adapted to this check it out . I'm one of those guy's I'm learning & wire my mic's ( sometimes ) but when that cover comes off the radio , " Leo No Touchy ":LOL: Thanks again for your help , till then , I can deal with it w/ no problems . 73 & God Bless , Leo
 
If you run those MB8719 chassis like the 148, 142 GTL or 2000 - all from Cobra, they usually offer a "Tone switch" to compensate for that shrill "fingernails on chalkboard" sound.
  • IF any of you ever had to listen to the "Domestic Discussions" that used to occur between Husband and Wife or Girlfriend to Boyfriend - you can understand the reference. For if someone raises their voice or inflections change to something more "Anxious" - you can easily see why hi-cut filters are a necessity - not just for car engine whine and spark noise - but to save our hearing from the tinnitus and rining of the ears that would occur after the discussion settled down.
Now if they USED to have it ON all the time (say for example you wanted a 10kHz (10kC) switch - you can use "TONE" switch for that purpose.

In Fact, Lou Franklin used to promote the IDEA of; if you needed real estate for that such a means to obtain channels - you can make the TONE switch your go-to. You can solder in the cap to make it more permanent. Else if the speaker needed more high-fidelity tone - you can take out that cap - remove it.

So this shrill sound is from a peaked (prolly' more for wattage than a working fidelity issue) set of coils and although you can EQ compensate thru the use of EMPHASIS filtering - you may not get the best results from the TYPE or ELEMENT the microphone passes into the radio.

Whether the Mic is a Dynamic or Ceramic or Electret - onto anything in between - they should remember that if you use a high-pitched or "trebley-tinny sounding" element to SEND out your signal - they usually would TUNE THE COILS for that purpose to maximize the audio BANDPASS that mic element has in frequency response.

So, that "Tinny shrill" sound, may be from the mic they used to tune the radio up with. If it was Bassy to begin with, I can see where they may have over-peaked the tuning to offset the effect to bring up the tone of the mic to a level that makes them understandable.

IN the effort of sending out a signal - you need the TONE switch due to the nature of the Mic Elements frequency response. You can't just "tweak" it away - for it receives and transmits the save frequency range - so if the Mic was Bassy and they needed to "sharpen" it's audio up remember the tuning method - because your hearing this event in the receive.
  • ("Sharpen" may indicate overmod, or they are placing too much audio into the AN612.
  • This extra audio drive can generate a muddy distortion effect that forces them to do the same thing - like clipper compression echo circuits you can install - they just tuned the IF used to offset to the higher end of the passband to cut off the lower bassy response and use the normal hi-treble sharper cut the IF Xtal filters provide for the Treble side - it narrows down the effort, and the audio coming from that radio will sound like dynamite to the ears of other listeners - but you get a very "narrow" and nearly mono-tone sound to the audio you receive..)
There's a lot to be said about microphones and SSB...
 

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