If you're adjusting for Squelch, don't use the RF generator to make a signal for that, it's 1800uV is for signals that are 20 over S9 - you do not need to use the RF generator for that.
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The Squelch pot, VR3 can be set to Mid-point and left alone once you have all your ducks in a row when your tuning is done.
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NB- off
ANL - Off
RFGain - Open all the way full gain
SQUELCH - Fully Counter Clockwise - to OFF
Just remember that you're working with a Radio that has a good effective AGC control - so you will have to exceed the uV limits of your RF generator - DON"T - at least you don't need to - save the trouble and continue to tune using the steps - then go back and tweak VR3...
1,800 uV is like someone parked in front of your house or under your antenna - and you're trying to SQUELCH them out - Remember that AGC is working in the radio AGAINST the Input Gain the Receiver has, so if you can't squelch them out - you already know that with this much signal arriving into your radio - it can do some damage - so why force the Signal Generator to do this step for you?
Here's what I do...it just simpler and easier less hassle because your taking and testing the radio for OEM specs - unless you;ve done a receiver mod, then OEM specs is what you tune and strive for...
- I do it this way, VR3 to minimum, Squelch control to minimum - as in you hear static hiss...
- Turn Squelch control to 1/4 - up from Minimum position - then turn VR3 until Static stops - you've engaged the Squelch control - note "o'clock" setting of the VR3 pot, is it near Noon? Then you're set.
- Else observe the Rotation of VR3 to open Squelch then close it
- - if you find yourself having SQUELCH ENGAGE turn-on BEFORE you reach noon (like say, 9 - or - 10 o'clock position - then something in the RX strip isn't quite right - you may have inadvertently tuned the RX strip for IF carrier - not your AM / SSB signals - so you may have over peaked a section of the Receive, which then affects the later stages PAST the section - recheck settings - retrace your steps and retune.- your Receiver is TOO quiet...
- IF you are finding VR3 has to be turned PAST noon, to say - 3 o'clock position - then the "L12" thru "L15" you need to check LINEARITY of SSB to AM - that may require you to look and observe the S/RF meter for activity in your re-tune session. You may have over peaked SSB to offset AM or vice a versa.
- VR3 being set to Mid-point is pretty much what Cobra wants to see
- - so if you see Squelch engaging sooner than Mid-point - the Receiver is TOO quiet - retune...
- - IF you see SQUELCH engaging LATER - PAST mid point - The Receiver is TOO noisy - potential Birdie or overpeaked IF section
- Remember that RX is finicky -Channel 1 and Channel 40 - tune for best level balance - then recheck on Channel 20
For Best results, remember the AGC is engaged in the radio - so unless you know how to turn it off, best to keep the RF signal Generator and it's RF output, to below 100uV - and worry about VR 3 like above.
Defeating AGC is not for the feint of heart, even Cobra doesn't provide the steps for it - it's not necessary.
If you do this, you are accepting the risks of potential damages to PIN diodes RF front end and FET's used to mix for IF signal processing - DISABLE TX MODE and prevent the Driver and Final from having power to key up - meaning you pull their Bias feeds - before you begin.
Disabling the AGC is not recommended - if you do - you are on your own.
Back to the 148's RX side...
When it's (VR3) at Mid-point , your ok, when it's not, remember to check the level of rotation VR3 needed - to just engage the Squelch when the Squelch control is off it's bottom stop - and ready to engage - you should be able to quiet the receivers own internal noise by just setting VR 3 to mid point, you don't need any more level control than that.
IF VR 3 quiets too soon, you may have missed a coil or over peaked the wrong coils in the wrong mode - reset and retune to rebalance the "hiss" level as well as VR3's action. You have a TOO QUIET Receiver.
IF VR3 needs more turn beyond mid-point before it quiets - then you may have over peaked - you have a noisy receiver and if can be from IF carrier onto unbalanced Bandwidth - tuned too close to Channel 1 or Channel 40.
