And no S/RF indication?
You have RX Green light, but when you switch - Key the mic handset you get to TX - no red light correct?
You have RX Green light, but when you switch - Key the mic handset you get to TX - no red light correct?
-
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Cobra 29 LTD Classic NO RX/TX HELP!!!!!!!!!!!!!
- Thread starter Buzzard78945
- Start date
Another step here to help, plug in the PA speaker in the EXT SP jack - and power up radio - any thunk or sounds from External?
No thud when I turn radio on with speaker plugged in to external speaker... when I work on a radio I pull the speaker cover I usually plug in external speaker
So if we can see about opening the PLL and see if we get LOCK...
Set Channel Selector to Channel 9 ...
Volume 50%
NB/ANL - Off
IF you have a Scope fantastic, but we don't need one at this moment...
You just need the DVM to measure a Test Point - they are simple "standoffs" from the board you can put a regular Test lead (they'll let you know if it's special purpose) and this test is Voltage reading to see if the PLL can send a voltage to tune an oscillator circuit that uses a Varactor.
To Test,
Do you have any Ceramic tip tools? Non Ferrous, Non Metallic - RF transparent type of tuning tools around?
Because you'll need to remove the Wax plug on L22 and around the Test Point Standoff resistors to get a good clean contact as well as ability to tune the slug without breaking it.
In the steps above, they mention an Oscilloscope - unless you had to rework a tuning circuits' bad NPO caps or a leaky Resistor - you can really do this without one for it can add more confusion that you don't need to have thrown at you right now.
We will do this a little differently - we locate the Cans were going to tune - and if needed - take a close up pic of them using your smartphone to help you orient them and remember their initial settings when you started - its' a documentation process step you will find useful in having to go back in and adjust something - at least you'd have a clue as to where you started at. I'm referring to the slug, its' slot - how far down it is in the form - can provide clues as to their condition and if someone tampered with them - they stopped in this position. So as we work thru the and walk thru the tuning - the slugs will play an important role in the start along into the final adjustment stages.
See below this post, there are two attachments - look for the Cobra29 TP2 - and review what I mentioned above.
It may not hurt to use a marker to "score" along the flat of the slug for Alignment. You can also see I labeled the two mentioned in the PLL Alignment Section. The TP2? You can just keep the DVM on that "post" for this entire test.
Why?
Now things will get dangerous. For if you can hear the RX hiss, that also may mean you can TX too - time to put a Dummy load on the Back of that radio to protect the Finals from blowing out due to NOT having any antenna or load connected to accept the power the Finals will put out.
As you adjust, the cans for RX and TX are slightly different to each other - so the radio will shift with an offset to align the frequencies it generates to meet the channel - this may put it out of lock. So be ready to adjust L22 to improve it's output so you can obtain the signal and the PLL can hold a lock again.
I'll stop here...for now... see below for details...
Set Channel Selector to Channel 9 ...
Volume 50%
NB/ANL - Off
IF you have a Scope fantastic, but we don't need one at this moment...
You just need the DVM to measure a Test Point - they are simple "standoffs" from the board you can put a regular Test lead (they'll let you know if it's special purpose) and this test is Voltage reading to see if the PLL can send a voltage to tune an oscillator circuit that uses a Varactor.
To Test,
- you apply the Positive (+) lead to the Open Bare Lead that is folded over to expose your connection point.
- The NEGATIVE lead goes to a simple IF Can Case .
- or if you wish to use one a Bare Wire Strip soldered across the gap between two IF cans can work too. But that type of test jig is only necessary for long test duration problem requiring a known mounting location to help support the test equipment grounding needs.
Do you have any Ceramic tip tools? Non Ferrous, Non Metallic - RF transparent type of tuning tools around?
Because you'll need to remove the Wax plug on L22 and around the Test Point Standoff resistors to get a good clean contact as well as ability to tune the slug without breaking it.
In the steps above, they mention an Oscilloscope - unless you had to rework a tuning circuits' bad NPO caps or a leaky Resistor - you can really do this without one for it can add more confusion that you don't need to have thrown at you right now.
We will do this a little differently - we locate the Cans were going to tune - and if needed - take a close up pic of them using your smartphone to help you orient them and remember their initial settings when you started - its' a documentation process step you will find useful in having to go back in and adjust something - at least you'd have a clue as to where you started at. I'm referring to the slug, its' slot - how far down it is in the form - can provide clues as to their condition and if someone tampered with them - they stopped in this position. So as we work thru the and walk thru the tuning - the slugs will play an important role in the start along into the final adjustment stages.
See below this post, there are two attachments - look for the Cobra29 TP2 - and review what I mentioned above.
It may not hurt to use a marker to "score" along the flat of the slug for Alignment. You can also see I labeled the two mentioned in the PLL Alignment Section. The TP2? You can just keep the DVM on that "post" for this entire test.
Why?
- - as you re-tune L22 - you'll see the DVM readings jump around - once they go steady, you have a lock, you may also hear a "hiss" or air-noise from the speaker - you have a receiver! TX? Don't push it yet....
- - Turn the Channel Selector slowly - you should hear the hiss - if the "hiss" disappears - then you've lost lock - take a moment and "tweak" L22 again to see if you can regain a Lock and the Hiss...
- Once you've got the Hiss again, try changing the Channel Selector to Channel 1 and Channel 40 bounce between the two several times using the Channel Selector clicking back and forth - to ensure the PLL and L22 can Lock on all the channels in between 1 and 40.
- Check your DVM reading on R88 and Change Channel to Channel 1 - note reading and Change to Channel 40 - this Reading should be 3.2 Volts - if not - Locate and Retune L19 until it's says so.
- Check R88 and DVM readings. When the PLL goes "out of Lock" it means it can't track the frequency the Oscillator uses. So the DVM readings are pretty much all over the place in high voltage readings of 6 volts or more or really really low voltage ones... That means it's out of lock and you have to "tweak L22" again to obtain and hold lock. To know you've got lock, is when that voltage stays steady at one set voltage.
- Set Cannel Selector to Channel 40 and Adjust L19 again for 3.2 volts.
Now things will get dangerous. For if you can hear the RX hiss, that also may mean you can TX too - time to put a Dummy load on the Back of that radio to protect the Finals from blowing out due to NOT having any antenna or load connected to accept the power the Finals will put out.
As you adjust, the cans for RX and TX are slightly different to each other - so the radio will shift with an offset to align the frequencies it generates to meet the channel - this may put it out of lock. So be ready to adjust L22 to improve it's output so you can obtain the signal and the PLL can hold a lock again.
I'll stop here...for now... see below for details...
Attachments
Ok! Good to know - nice to have someone like you aboard - willing to make this work - thanks.
Ok, let's see - you have PA but no "thunk" - ok, let's look or jump ahead a little - can you adjust the Squelch control at all? I mean - turn down the knob all the way - and power up then power off - any thunk?
Do the same on it all the way up - same result or do you hear a thunk now?
- IF so it's wires then are reversed - just reverse the header - unsoldering then re-soldering them in the other direction or check the pot itself - and it uses two wires - that go to the knob. can you see the condition of the wires? Make sure they are not disconnected from the Pot.
- There is a Squelch Trimmer pot on the board - VR3 - check it's condition. Tweak it with the volume turned up 70% or so...adjust the Squelch control fully Counter Clock wise for this to see if you hear a hiss.
Trace those wires back to the board - they usually go to a header - look on the bottom side of the board for the headers traces and check their solder condition - reheat them if needed and check for Squelch operation - it needs to be fully counter clockwise to be considered off. Tweak VR3 as needed...
VR 3 is located by and towards the Front panel from the TR23 Regulator.
Ya I can do that shouldn’t be bad... just mark the slug ( so you know where to put it back at... I don’t have a scope or freq. counter )
alligator clip dvm on
Turn slug on each channel until it says at certain voltage
I do have:
Dosy meter
Mfj dummy load
Dvm
I don’t have:
Frequency counter
oscilloscope
Most likely I won’t be able to do till day after tomorrow
like I said PLL HAS ALL the proper voltages
TR23 has proper 8 volts
RX/TX light is green, turns Red when you key mic
PA mode does work with aux speaker
Then until we get some kind of speaker - hmmm...
Have you found Squelch wires? The pair that are from the SQ Pot, down to the board?
Have you found Squelch wires? The pair that are from the SQ Pot, down to the board?
One last suggestion, then I'll call it a night...
Does the Mic cord seem to have any damage?
Un plug it, try a manual short test to see if the socket is ok...
With the radio on, Try Shorting the two bottom pins of the Mic socket the side that has the INDEX Notch, Pins 1 and 4 Together. Those two are the on the (usually bottom) portion of the socket that are by the Index Notch and Pin 1 is on one side lower, Pin 4 is the opposite side lower...across from each other on that Index Notch side...
Why this? To see if the CB/PA switch or Mic Jack is goofy. You may have a bad wire in the Mic cord...OR Mic wire from the socket that is to Pin 4 may have a cold solder joint...
In PA, it would not matter if Pin 4 worked or not, you're using Pin 1 - Ground, Pin 2 - Audio, Pin 3 - when you're in TX Or PA mode - the Speaker is automatically grounded by the CB/PA Switch setting-THRU PA jack. It still uses 4 - but if it's not receiving - as you said, you can talk to yourself all day...
Does the Mic cord seem to have any damage?
Un plug it, try a manual short test to see if the socket is ok...
With the radio on, Try Shorting the two bottom pins of the Mic socket the side that has the INDEX Notch, Pins 1 and 4 Together. Those two are the on the (usually bottom) portion of the socket that are by the Index Notch and Pin 1 is on one side lower, Pin 4 is the opposite side lower...across from each other on that Index Notch side...
Why this? To see if the CB/PA switch or Mic Jack is goofy. You may have a bad wire in the Mic cord...OR Mic wire from the socket that is to Pin 4 may have a cold solder joint...
In PA, it would not matter if Pin 4 worked or not, you're using Pin 1 - Ground, Pin 2 - Audio, Pin 3 - when you're in TX Or PA mode - the Speaker is automatically grounded by the CB/PA Switch setting-THRU PA jack. It still uses 4 - but if it's not receiving - as you said, you can talk to yourself all day...
On a project...
To touch back on the Squelch...
I have encountered bad wiring in the Squelch control circuit. It simply is a design to have high Hysteresis
In simpler terms,
a circuit designed to stay off as a condition,
It uses a Control Signal as the means to turn on and off...
but when a threshold is reached, the circuit turns on - And stays on
until the Control signal has fallen (or risen) past a limit.
In the Grey area in the Graphic above, that region is considered the "Hold-on condition"
even when the control signal varies.
Link to the Article Here
Squelch can be finicky - I'm brining this up even if it's not the CAUSE of your condition, it's simply here to document my thoughts on a previous repair that exhibited, by your description - similar symptoms...
It was from a previous mod done to the radio (not yours a radio I had bought used).
They wanted a variable power carrier - so they attempted to install it using the Squelch Control and the current the mod pushed thru the pot was too great and caused the Squelch control to open - it popped, the resistor substrate that makes the pot variable - opened up on one end. It broke the power flow in the circuit.
For Squelch to work, a current has to flow thru the circuit in such a way as to maintain a balance to oppose another current flow from entering into it.
This Balance make the Squelch circuit work like it does...
In shorter words, I had to replace the Potentiometer - but I had to go thru all of the above to learn that Open lines can be just as hazardous to getting a radio to work as much as a dead short...
Ok, back to you!
To touch back on the Squelch...
I have encountered bad wiring in the Squelch control circuit. It simply is a design to have high Hysteresis
In simpler terms,
a circuit designed to stay off as a condition,
It uses a Control Signal as the means to turn on and off...
but when a threshold is reached, the circuit turns on - And stays on
until the Control signal has fallen (or risen) past a limit.
In the Grey area in the Graphic above, that region is considered the "Hold-on condition"
even when the control signal varies.
Link to the Article Here
Squelch can be finicky - I'm brining this up even if it's not the CAUSE of your condition, it's simply here to document my thoughts on a previous repair that exhibited, by your description - similar symptoms...
It was from a previous mod done to the radio (not yours a radio I had bought used).
They wanted a variable power carrier - so they attempted to install it using the Squelch Control and the current the mod pushed thru the pot was too great and caused the Squelch control to open - it popped, the resistor substrate that makes the pot variable - opened up on one end. It broke the power flow in the circuit.
Basic Example
For Squelch to work, a current has to flow thru the circuit in such a way as to maintain a balance to oppose another current flow from entering into it.
This Balance make the Squelch circuit work like it does...
- - to keep it FROM conducting and stay "Off" - or- to Stay ON and keep working (quieting)...
- the THRESHOLD of when the Circuit is to change state, is designed as like a Trigger the circuit turns on or off is based on two values..
- - when you turn up the squelch knob to quiet the noisy traffic on your radio - you change the way that current flows thru the circuit - you upset the balance and the imbalance turns the Squelch Circuit "On".
- - In the above example - a voltage changes - this action can be considered a Trigger voltage
- Power then flows from a Regulated set voltage to switch the state of another Transistor in the chain - which then changes the Power flow thru another Transistor that can be used to control power flow - turned on - power is sent into the Transistor and into Ground like a Shunt - or in this case - to MUTE an audio signal line.
- - when the Squelch turns back off, it releases the control the Squelch has to QUIET the signal.
- The Squelch setting didn't change, the Power flowing into the Squelch control Network did.
- - The other voltage value used in this circuit is the STRENGTH of the signal arriving into the receiver. When the signal is weak, the flutter and fluctuation of the incoming signal affects this SECOND value to a higher degree. This can make the Squelch control chop or Mute portions of the signal - so the circuit is designed to HOLD squelch in a condition (off) until the ability of the Radios' AGC circuit fails to keep the signal above this second value.
- The Circuit is a high gain switch, but it's supported with capacitance that slowly drains off this trigger voltage but also allows the Trigger voltage to hold the Squelch "Off" for longer period of time of release. But, instead of "fading" out the volume as if its' a linear amp, it's more of a sudden change of state - like a switch.
- There are at least two smaller circuits in the Squelch Control system
- - a buffer amp TR6 that monitors the AGC line and a REFERENCE voltage...
- - TR6 is a Switch biased to be turned on at all times when the SQUELCH knob is set to it's lowest setting.
- This reduces the power to control another circuit to keep it turned off...
- When the knob is turned up - more power flows out of the Network circuit and TR6 tries to turn off...
- - TR7 is a simple amp arranged to await for a control signal from the Buffer, TR6, to turn on, else it is kept off all the time...
- This Transistor TR8 with it being tapped into the Audio Line arriving Before the Audio Amp, is used to take away (Mute) signal before it arrives to that Amp. It uses TR7's output status as this control - when TR7 is biased on, it's control output to TR8 is too low for TR8 to turn on so it stays off and audio signal passes thru into the Audio Amp..
- Using this method of shunting signal effectively quiets the radio because the Squelch Amp switch engages and sends Audio signal into ground only when TR7 stops conducting, and allows the voltage tap for TR8's Base (R26) to rise and turn on TR8's base to send signal to ground. .
- To make this happen, the two references are applied to two different locations in the circuit. AGC is first developed thru a Divider circuit of power thru a Resistor Divider R15 and R16 - With R15 from the Regulated side, and R16 from the AF Detector Rectified carrier signal side.
- Note Diode D5 is oriented towards the source of the AF signal - so power flows OUT of the R15/R16 combination and into the AF Detector circuit when STRONG signals and Signals with Carrier are present - making current become rectified and flow away from the Divider circuit - into the diode ion to the AF detector network,.effectively REDUCING the power available in the AGC line for the Squelch to use. A drop in power available.
- - this is important to have - in order to obtain and use the DIFFERENCES present between the KNOWN reference and the Variable or RECEIVED SIGNAL STRENGTH reference.
- It is designed as a Differential amplifier to offer Control Characteristics for the Squelch to work as the Makers intended.
- The output of the TR6 in graphic uses the Regulated Reference (8 Volts) as a digital on/off signal for TR7 to Toggle on or off. When TR6 turns off, R24 can then flow power into the Base of TR7 - to turn it on.
- However, R93 a very highly ohmic resistor 3.9 Meg-ohms - provides a tiny small level of current flowing thru it between both TR6 and TR7 all the time to change the behavior of Squelch control as a means to Hold Open the squelch for Signals strong enough to break the squelch, and stay off when noise drowns out the signals - per setting by the operator.
- -R93, is arranged to keep the Circuit On and Delay when the Circuit turns off - this affects how TR8 responds
- The Hysteresis of the Circuit is the reason this resistor is placed where it is in the control circuit - to allow the Squelch some lag time between on and off conditions so the Audio signal is not chopped and distorted from the more rapid opening and closing of the Squelch without this Resistor. This design and value - used this way provides Hysteresis and helps to slow the "chopping" effect down.
- - it is applied thru the Base of TR6 thru a high value resistor (680K) and the Squelch Control Adjust Circuit network of R23 (3.3K), VR2 50K Variable and R101 (15K)
- VR 2's adjust arm is fed TR6's Divider voltage and the Squelch is fed the AGC (R15/R16 divider - side control signal and is "trimmed " to a finer degree thru the use of VR3 - a simple trimmer to balance the divider circuits' operational voltage to match the operational "knee" characteristics of the two stage amplifier the Squelch amp is TR6 and TR7
- - being fed by the AGC signal from the AF Detector circuit into the Divider Network the power can be adjusted by VR 2 to finely control when TR6 turns on, that when it does conduct, it removes power from TR7's Base, and turns Off TR7, so that TR8 can Turn On and Operate the Squelch as a Mute function.
- - Power that flows thru the Divider of R92 (680K) (Regulated) and R23 (3.3K) (AGC + Variable) is the input signal power source to make TR6 turn on and flow power thru it from R24 (10K) dropping power thru the resistor which then removes power from the base of TR7.
- TR7's Base has no power to stay on - it stops flowing power thru it's Collector to Emitter junction - stopping the flow of current that kept TR8 from turning on.
- TR8 is biased in a way that when TR7 is on, TR7 keeps power flowing thru itself from R26, TR8 cannot turn on, it's Base power is impeded by R25 - so TR8 stays off and lets signal pass, when TR7 turns Off, power can now flow from R26 thru R25 into TR8 and turn On.
- TR8 can also be used for when the System is unstable unable to function and provide a frequency lock - TR8 can have power applied from the Out Of Lock condition (if the PLL has a means to tell the system it's not able to work properly and outputs a High State line an turn on preventing Audio from being heard so the operator can then take action.
In shorter words, I had to replace the Potentiometer - but I had to go thru all of the above to learn that Open lines can be just as hazardous to getting a radio to work as much as a dead short...
Ok, back to you!
Last edited:
i have lock on all channels and tuned For 3.2v on ch40
i have static now, very poor recieve, i can tell someone is keying but its all jumbled muffled scratchy
still just red light when keying and no power out...
i finished reading through what you sent the other day i get how squelch works now 
... i better under stand the schematic... just to recap... i do have static now!!!! i also did replace the volume/squelch pot. because the volume control was ever so sightly bent... may have been droppped!!!???? then proceeded with your voltage checks/adjust at L22 and L19.... PLL locks now and i have Static...
Note... I didnt plug in my external speaker until was done with voltage checks and adjustments... but at the end of the day we have something coming out of the speaker now! Thanks
also i had my wife transmit from radio in her truck to the shack and i was able to tell someone was keying by the change of static, THE METER NEVER MOVED!, and it was just bla coming out of the speaker not able to understand anything...
i have to call it a night boss lady is getting pissy...
THANKS HANDY ANDY
... i better under stand the schematic... just to recap... i do have static now!!!! i also did replace the volume/squelch pot. because the volume control was ever so sightly bent... may have been droppped!!!???? then proceeded with your voltage checks/adjust at L22 and L19.... PLL locks now and i have Static...Note... I didnt plug in my external speaker until was done with voltage checks and adjustments... but at the end of the day we have something coming out of the speaker now! Thanks
also i had my wife transmit from radio in her truck to the shack and i was able to tell someone was keying by the change of static, THE METER NEVER MOVED!, and it was just bla coming out of the speaker not able to understand anything...
i have to call it a night boss lady is getting pissy...
THANKS HANDY ANDY
Ok, will give it a break for now...
I don't think the radio is SEVERELY damaged, but if the radio has been dropped - we may have more of physical than electrical problem on our hands.
Ok, that may mean you'll have to pull a part or two - you up to it?
This is the Driver and Final section...although I do not think it is bad per-se. It is an area to check for cracks and broken joints. There is a big heat sink panel back there that is bolted to the board but not sure if it survived the jostle / faceplant from the previous owner.
Parts can shift, and boards can crack and solder joints can come undone. IF you're having problems more with garbled weak audio but you have noise - it may be from parts that got shifted...
Note too, this radio is stock virgin - all parts are in place.
The other aspects may be it need a good tune up but right now you seem to have a lot on your hands.
Look above and compare it to your board - should look pretty much the same...
Will talk later...
I don't think the radio is SEVERELY damaged, but if the radio has been dropped - we may have more of physical than electrical problem on our hands.
Ok, that may mean you'll have to pull a part or two - you up to it?
Wanted to give this to you too...This is the Driver and Final section...although I do not think it is bad per-se. It is an area to check for cracks and broken joints. There is a big heat sink panel back there that is bolted to the board but not sure if it survived the jostle / faceplant from the previous owner.
Parts can shift, and boards can crack and solder joints can come undone. IF you're having problems more with garbled weak audio but you have noise - it may be from parts that got shifted...
Note too, this radio is stock virgin - all parts are in place.
The other aspects may be it need a good tune up but right now you seem to have a lot on your hands.
Look above and compare it to your board - should look pretty much the same...
Will talk later...
it’s all stock as far as I can tell... JP36 still in place (no cap installed) factory final still in it ( no mosfet ) cap over by the transformer factory size... D9 in place
Can you tell me more about the operation of the radio?
You said your wife was talking and you couldn't hear her very well or even have any meter movement...
That can mean a failed part in the RX chain - or out of tune can...or even a switch in the Wrong Position.
Set you radio...
You have an LTD - but the above is pretty much the Same panel...
Starting from the LEFT
Set S/RF / SWR / CAL - to S/RF
Set NB / ANL / ANL / OFF - set to OFF
Set CB / PA to CB
Tone (if you have one) To Hi - helps with hearing hiss for RX noise level
Set BRT / DIM to your preference Bright or Dim
RX/TX light - Green for RX, RED on TX...
ANT - Glows RED when you have poor antenna connection or problems with your antenna.
Squelch - Full Counter Clock wise - OFF
Dynamike - Up Clock Wise - ON
RF Gain to MAX
Delta Tune to CENTER (you may be able to feel a detent)
The Radio has a Delta Tune control - it controls the RX FREQUENCY of what you hear as stations tuned into your Receive Frequency - on the channel.
SWR CAL used to CALIBRATE your antennas' POWER for tuning your antenna - you compare Power going to the antenna Forward - against Power Not being Used by the Antenna and is being returned to the Radio (REFLECTED) - this is a ratio - a number - a performance indication of how well your system can be tuned to perform.
Ok, my main concern?
Delta Tune...
In the older days, most radios used Crystal Synthesis - a bank of Crystals that were "mixed" with another bank and when placed thru a tight filter, gave you 23 channels. Now we have 40 but there are still radios out there that are "Fixed" in frequency but slightly off to another radio - you don't hear the differences much, but they can sound distorted. This can happen if you use this radio to talk to another that isn't tuned to your frequency you're receiving. Yes, they are on the same channel, but not the EXACT frequency in the channel band plan.
Check also - the operation of the RF gain control - it has to be fully on - turned fully Clockwise to make the receive have it's highest gain so you can hear distant stations.
Ok, I'm going to stop here and let you play with your radio a little bit I want to know what it is you're dealing with when it comes to not being right...
You said your wife was talking and you couldn't hear her very well or even have any meter movement...
That can mean a failed part in the RX chain - or out of tune can...or even a switch in the Wrong Position.
Set you radio...
You have an LTD - but the above is pretty much the Same panel...
Starting from the LEFT
Set S/RF / SWR / CAL - to S/RF
Set NB / ANL / ANL / OFF - set to OFF
Set CB / PA to CB
Tone (if you have one) To Hi - helps with hearing hiss for RX noise level
Set BRT / DIM to your preference Bright or Dim
RX/TX light - Green for RX, RED on TX...
ANT - Glows RED when you have poor antenna connection or problems with your antenna.
Squelch - Full Counter Clock wise - OFF
Dynamike - Up Clock Wise - ON
RF Gain to MAX
Delta Tune to CENTER (you may be able to feel a detent)
The Radio has a Delta Tune control - it controls the RX FREQUENCY of what you hear as stations tuned into your Receive Frequency - on the channel.
SWR CAL used to CALIBRATE your antennas' POWER for tuning your antenna - you compare Power going to the antenna Forward - against Power Not being Used by the Antenna and is being returned to the Radio (REFLECTED) - this is a ratio - a number - a performance indication of how well your system can be tuned to perform.
Ok, my main concern?
Delta Tune...
In the older days, most radios used Crystal Synthesis - a bank of Crystals that were "mixed" with another bank and when placed thru a tight filter, gave you 23 channels. Now we have 40 but there are still radios out there that are "Fixed" in frequency but slightly off to another radio - you don't hear the differences much, but they can sound distorted. This can happen if you use this radio to talk to another that isn't tuned to your frequency you're receiving. Yes, they are on the same channel, but not the EXACT frequency in the channel band plan.
- - are you checking the operation of the Delta Tune?
- - there is a can "L23" which handles IF fro RX, as well as "L24" - being the main tuning coil for the 10.240 Xtal - the true Heart beater (a Required function) of the radio.
Check also - the operation of the RF gain control - it has to be fully on - turned fully Clockwise to make the receive have it's highest gain so you can hear distant stations.
Ok, I'm going to stop here and let you play with your radio a little bit I want to know what it is you're dealing with when it comes to not being right...