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Strange drop in sensitivity on V6 #ubitxv6

 

Hey all!

I am having a rather strange drop in sensitivity on my V6 after carrying it up to the cabin.? The unit was well padded in a cardboard box riding in the cab of the truck so it wasn't bounced around a lot.? After hooking it up I noted that the background noise was all but gone and there was no reading on the S-meter.? When a very strong signal was received I would get an S2-S3 reading and I am having to turn up the volume control much higher.? I compared some signal levels against my Yaesu FT-707 and today the background noise on 40M was at S9 and 0 on the BITX S-meter (from the AGC board) using the Nextion with Ian's 1.2 firmware.? I also compared some signals that were about S7 on the BITX and they measured +20 on the Yaesu.? Radios are using the same antenna with a switch so I can immediately switch and compare signal levels.? I feel the AGC board is still working since a very strong signal would be overwhelming if switched off.

I am up here in the middle of nowhere with only an antique 30 MHz analog scope and a meter so I'm looking for suggestions as to where to look or if I should just re-calibrate the S-meter.? I have removed the cover and checked for anything that might have jarred loose during the trip and lightly flexed the PCB and found nothing. I can still make contacts and carry on QSOs but the "quietness" disturbs me...? I have bought a used West Mountain Radio CLRdsp (should be here Monday) in my quest to kill/fight the "birdies" produced by my solar charge controllers and it also contains an amplifier so that will get my volume back up but it is more of a band-aid.

73,

Justin B.
KI5GKD
 

If you can make contacts, the. Digital board, the RF coils and crystal filter etc are all working perfectly. I would think the volume control is busted. What happens if you touch the detector diode with a screw driver. It should be an uncomfortably loud sound. If not, check around the audio preamp.
Next touch pin 2 of the LM386. Loud noise?
- f

On Fri 14 May, 2021, 9:36 AM Justin Bowser - KI5GKD, <justin.bowser@...> wrote:
Hey all!

I am having a rather strange drop in sensitivity on my V6 after carrying it up to the cabin.? The unit was well padded in a cardboard box riding in the cab of the truck so it wasn't bounced around a lot.? After hooking it up I noted that the background noise was all but gone and there was no reading on the S-meter.? When a very strong signal was received I would get an S2-S3 reading and I am having to turn up the volume control much higher.? I compared some signal levels against my Yaesu FT-707 and today the background noise on 40M was at S9 and 0 on the BITX S-meter (from the AGC board) using the Nextion with Ian's 1.2 firmware.? I also compared some signals that were about S7 on the BITX and they measured +20 on the Yaesu.? Radios are using the same antenna with a switch so I can immediately switch and compare signal levels.? I feel the AGC board is still working since a very strong signal would be overwhelming if switched off.

I am up here in the middle of nowhere with only an antique 30 MHz analog scope and a meter so I'm looking for suggestions as to where to look or if I should just re-calibrate the S-meter.? I have removed the cover and checked for anything that might have jarred loose during the trip and lightly flexed the PCB and found nothing. I can still make contacts and carry on QSOs but the "quietness" disturbs me...? I have bought a used West Mountain Radio CLRdsp (should be here Monday) in my quest to kill/fight the "birdies" produced by my solar charge controllers and it also contains an amplifier so that will get my volume back up but it is more of a band-aid.

73,

Justin B.
KI5GKD

 

On Thu, May 13, 2021, at 11:06 PM, Justin Bowser - KI5GKD wrote:
West Mountain Radio CLRdsp
Hi Justin,

Can you provide a little more detail on the AGC used?? Also, what happens when you turn off the AGC?

As to S readings, at best they are relative and very unique to any given radio.? There is not a true standard to "calibrate" to it.? There are tools in both the Nextion display and the Memory Manager software that do not require any other tools.? Here is a screenshot of the section of the ?BITX Memory Manager software.



You can use the "S Meter Assistant" to help in the setup.?


Note that the different "Samples" are different curves that the Assistant uses to set each of the 8 different S meter points.? To use it you find a clear frequency and press the Min Value Read from button, then find a strong signal and press the Max Value Read from button.? I then adjust the Max value to get what I think is correct based on another radio.? You can select the different Samples to get the curve you like.? I used the Sample3 setting.

Do not forget to save your settings using the Memory Manager before and after each adjustment.? I always save what is in the radio first, adjust the settings, save the new settings to a new file, and then try them out.

In case you do not have the Memory Manager SW it is here:


Have fun in the Low Noise environment, I am jealous :-)
73
Evan
AC9TU

 

Ashhar -?Thanks for the suggestions, I will try them later today and report the results.? I hadn't considered the pot due to it's ability to vary the volume coupled with the lack of S-meter reading.

Evan - It is the board supplied by kit-projects based on the ND6T design.? Last evening I played with the AGC and verified that while listening to a QSO containing weak and strong if I turned off the AGC the "strong" signal blasted obnoxiously and the "weak" signal remained about the same.

73,

Justin B.
KI5GKD
 

On Fri, May 14, 2021 at 10:07 AM, Justin Bowser - KI5GKD wrote:
Evan - It is the board supplied by kit-projects based on the ND6T design.? Last evening I played with the AGC and verified that while listening to a QSO containing weak and strong if I turned off the AGC the "strong" signal blasted obnoxiously and the "weak" signal remained about the same.
Justin,
I worked on a v6 for a friend and found that the S meter signal off of the ND6T design varied with fast and slow response settings, with no signal on-off.? I ultimately went to a separate feed off of the audio header with an LM358 amp, 2 resistors, and diode as KD8CEC built for the first one.? I used a perf board, 8 pin socket and a header soldered to the edge of the perf board.? Here is a picture of the prototype board:
 

Ashhar - Touching pin 2 of the LM366 does nothing, touching pin 3 produces a bit of a squeal but not overly loud.? I'm not sure which is the detector diode, could you give me a part callout?

73,

Justin B.
KI5GKD
 

Evan - I have built the circuit for the S-meter but it is about 300 miles away!? I woukd have thought nothing about the S level response if the volume hadn't dropped at the same time.? It used to be that when I had the volume pot turned to full loud the sound was very loud and distorted, now it's not.

Justin B.
KI5GKD
 

Justin,
I believe that Ashhar Farhan is referring to D5 in the product detector stage.? That goes through the preamp Q70.

Where did you tap into the audio chain to get the signal for the AGC?? Could that be causing a load on the audio sections?? Did you install the RF attenuation variable resistor (I highly recommend doing that as decreasing the RF can make the signal distinction better.? That is one of the contesting suggestions for all rigs.)??

Based on what you have stated so far, I do not believe that you have an issue with sensitivity, rather you are in a quieter setting and the S meter response is different.?

Just my thoughts.
73
Evan
AC9TU
 

Justin,

The fact that you are away from AC power lines (I am assuming that is the reason for the solar panels) would mean that any tests that rely on AC hum may not work.? The loud "squeal" when you touch pin 3 (Ashhar Farhan got the pins backward) could be from the loudest noise source in your cabin: the solar panel controllers.? The solar panels could drown out any of the 60 cycle fields from the inverters.?

The fact that you can transmit and receive means that it is working.? The reduction in receive signal may be from the AGC losing connection.? Try jumpering around the AGC, or better yet is to remove and jumper to see if the signal goes up.

73
Evan
AC9TU
 

Even and Ashhar - The middle leg of D5 produces a small "squeal" (about the same level as that of pin 3 of the amp) as well so maybe everything is OK.? As soon as I find my USB cable I'll re-calibrate the S-meter and consider it done.? Not really set up to do any fine soldering up here so any testing that requires soldering on the board will have to wait until this fall when I'm back in civilization! :-)

Thanks for the help and sanity check.

73,

Justin B.
KI5GKD
 

Evan,

The AGC board I installed is at this link which shows how it is conjnected to the uBITX PCB.



73,

Justin B.
KI5GKD
 

... connected...

Man, I hate this laptop keyboard...
 

Justin,

That is the same way that I connected the AGC for my friend's ?BITX.? Was not sure if you did the connection to the board or the volume control.

I complain about keyboards and spellcheckers all the time!? Of course, it isn't my typing skills that are at issue ;-)

73
Evan
AC9TU
 

I understand exactly where you're coming from!

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