The 148 GTL-DX / 360FM Clarifier cct

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cb4ever104
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The 148 GTL-DX / 360FM Clarifier cct

Post by cb4ever104 »

Hi All .

Feeling generous today , so I just thought I'd share my recent bit of "mod" work with you . I've been taking some of my radios out over the last few weeks and giving them a few hours run time . I was using my mk2 360FM this week . There was some Stateside skip here yesterday and one of the breakers said to go to XX0 . Anyway . I go to the 5 frequency and use the Coarse to go down 5 . Realised that I was just a bit off , and couldn't get him properly . Strange . Anyway . Got the radio on the bench . Here's what I had .

On TP3 . Coarse from full left to full right

AM 10.5Khz
USB 9Khz
LSB 12Khz

Now , to be honest I'm not entirely sure why there should be such a variation between the modes . The Fine/Coarse cct doesn't change between modes . They only change between RX and TX . I'm assuming that it's due to slight mode voltage and component differences in L21 through L26 and the caps in that cct . Anyway . That really wasn't something that I wanted to investigate , although there might be a slight issue in there on the USB line ,so I didn't bother messing about with that . I just wanted an easier , quicker way to get my USB slide to reach -5Khz and-+5Khz . Here's the circuit .

Clarifier.JPG

On RX . The main 8V gets fed through the 1K "Fine" and the output of that (7.2V at centre) gets passed through D85 , and the resulting 6.5V gets fed to one end of the 20K Coarse . The other end of the Coarse has a 3.3K ohm resistor which then gets fed to earth . There's about 1V on the resistor side . So , that means we have a 5.5V swing from left to right (6.5V - 1V) on the output of the Coarse , which goes to the main varicap D40 and which varies the capacitance on the main 15Mhz crystal .

So I needed to get a bit more voltage swing on that line . The easiest way for me was to "play" with R232 . That's a 3.3K ohm . I changed that to a 1K , which brought the voltage down to virtually 0V on that side giving me an extra volt . So now I have a 6.5V left to right swing on the output of the Coarse . Rechecking the Coarse values on TP3 I now have :

AM 12.8Khz
USB 10.8Khz
LSB 14.6Khz

Perfect . Job done . I now have +/-5.4Khz on USB . After changing the resistor you'll need to realign that oscillator stage again and the TX adjust as well .

Sammy

PS Just to add . On TX the RX voltage to the "Fine" gets cut off , and the main TX 8V gets fed through D84 to one end of the Coarse only . That's why the Fine only works on RX . That 8V TX voltage may be slightly different compared to the 8V RX voltage , so that's why you've got VR6 to adjust the voltage to the Coarse on TX to match RX .
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Re: The 148 GTL-DX / 360FM Clarifier cct

Post by 13EL121 »

I had a few SS360FM with the Coarse issue. Always replaced the 3.3k resistor R232 as you did. I used a 1.8k. This did the job. Often the France SS360FM are known for this issue starting seriel numbers 5 or 7.
73 Ralf
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Re: The 148 GTL-DX / 360FM Clarifier cct

Post by 13EL121 »

The issue is well known. But I wouldn't replace the resistor with a wire. This gives to much slide and drift.
IMG_20220206_105643.png
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Re: The 148 GTL-DX / 360FM Clarifier cct

Post by cb4ever104 »

13EL121 wrote: 06 Feb 2022, 09:57 The issue is well known. But I wouldn't replace the resistor with a wire. This gives to much slide and drift.
I'm happy with that Ralf . I'd never seen that article before . Which means that I actually managed to come up with a valid solution myself :)

If I keep going like this I'll be an expert in about a 1000 years :)
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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Re: The 148 GTL-DX / 360FM Clarifier cct

Post by 14CS06 »

Hello

it was already existing on the Super star 3900 R137 1K :thumbup:

@+
Claude
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Re: The 148 GTL-DX / 360FM Clarifier cct

Post by cb4ever104 »

14CS06 wrote: 06 Feb 2022, 12:52 Hello

it was already existing on the Super star 3900 R137 1K :thumbup:

@+
Claude
Merci beaucoup Claude !
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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