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T4XC problem

 
Edited

Good evening!?

I need to pick the brains of the drake GURUs

I have recently acquired a R4C (25657) and T4XC (27010). I have purchased proper interconnect cables. I have gone through alignment and cleanup of the R4C with minimal issues. I found a 25.1MHz xtal that was off frequency. I replaced with one purchased on eBay that was closer in frequency. Mostly all is well with the R4C except a strange noise that is noticeable when switching from USB to LSB which may be a bad cap that I haven't tracked down yet.

Here's the issue I'm having with the T4XC. Going through the "carrier oscillator, filter match and balance modulator" (5-9) alignment in the manual I cannot get things sounding correct on LSB. I have gone through this section several times with the same results: crappy sounding audio on LSB and decent audio on USB. Section "D" mentions to adjust C6 for exactly 5645 kHz. When I do this and switch to LSB I see a drop in oscillator frequency of 450-500 Hz. If I try to adjust C6 to 5645 Hz while in LSB mode, there is little change to oscillator frequency and I can completely remove trimmer screw. I have tried doing this alignment both connected to and disconnected from the R4C.

I am thinking this frequency shift is the reason the LSB audio is not making it properly through the filter and sounding like crap but I have no idea where to go from here.?

I am not an expert radio tech by any means but i do have some knowledge and a few decent pieces of test equipment.

PLEASE HELP! I want to put these twins back on the air where they belong

Chris Faas
W5CUY
 

Chris,
The T-4XC carrier frequency should not change between sidebands.? Yes, you are probably correct, that is the problem.

The carrier oscillator and the filter selection are isolated by the IF amp so even a bad filter shouldn't cause the frequency change.
I would measure the supply voltage (zener CR1) during switching.? And/or disconnect the RTTY line and CW line, those do change the
frequency (but not due to sideband).
Strange problem.
73,
Gary
WB6OGD

?
 

I¡¯m thinking that the key will be found in the mode switching. For some reason, the transmitter is shifting as if it¡¯s in CW mode.?

I agree that it probably isn¡¯t a bad filter.?

73,

Steve Wedge, W1ES/4

Time flies like an arrow. Fruit flies like a banana.


Sent from Proton Mail for iOS


On Wed, Apr 5, 2023 at 11:46, wb6ogd <garywinblad@...> wrote:

Chris,
The T-4XC carrier frequency should not change between sidebands.? Yes, you are probably correct, that is the problem.

The carrier oscillator and the filter selection are isolated by the IF amp so even a bad filter shouldn't cause the frequency change.
I would measure the supply voltage (zener CR1) during switching.? And/or disconnect the RTTY line and CW line, those do change the
frequency (but not due to sideband).
Strange problem.
73,
Gary
WB6OGD

?
 

Measured voltage at CR1 while switching:

USB 13.47
LSB 13.41

will try the rest of your suggestion when I have a little more time.?


thanks!
 

Ok, well that isn't the problem...
Steve suggested the Function switch since it does change the freq for CW but you are not
switching that switch when you change sidebands...
Strange problem!
73,
Gary
WB6OGD

On 04/06/2023 12:58 PM radiow5cuy@... wrote:


Measured voltage at CR1 while switching:

USB 13.47
LSB 13.41

will try the rest of your suggestion when I have a little more time.?


thanks!
 

Ok, figured it out.?

?

Q4 (the RTTY transistor) was bad. I don¡¯t plan to run RTTY or any other digital modes on this setup so I just left Q4 disconnected.?

Now the carrier oscillator frequency is stable while switching between side bands. Now LSB and USB both sound great! Thanks for the help!

Hopefully my schedule will allow me to check in to the next net.

?

73

Chris - W5CUY

1st rule of intelligent tinkering - save all the parts.

--?Source Unknown
 

Chris,
Great work.
You can still run RTTY and digital modes, they use audio signals now.? Old fashioned FSK really isn't used anymore anyway.
73,
Gary
WB6OGD
 

Nice catch, Chris!

73,

Steve Wedge, W1ES/4

Time flies like an arrow. Fruit flies like a banana.


Sent from Proton Mail for iOS


On Tue, Apr 11, 2023 at 23:11, wb6ogd <garywinblad@...> wrote:

Chris,
Great work.
You can still run RTTY and digital modes, they use audio signals now.? Old fashioned FSK really isn't used anymore anyway.
73,
Gary
WB6OGD
Jim W7RY
 

¿ªÔÆÌåÓý

Says who?? You? Better check your facts....

That's all I use for RTTY.

Jim W7RY



On 4/11/2023 10:11 PM, wb6ogd wrote:

Chris,
Great work.
You can still run RTTY and digital modes, they use audio signals now.? Old fashioned FSK really isn't used anymore anyway.
73,
Gary
WB6OGD


--
Thanks and 73, Jim W7RY
 

Ok Jim,
I am not up on the latest vintage trends I guess, hi hi.
I don't know how to hook my computer to the FSK jack.
73,
Gary
WB6OGD
Rick WA6III
 

Back in the mid 70's I had a Model-19 teletype set up complete with the cabinet and tape reader/puncher just like the one in the following You-toob? Mine had the sound-deadening cover so it didn't drive me out of the room!

https://www.youtube.com/watch?v=jxkygWI-Wfs

When I got my new C-Line, I connected the TNC to the T-4XC so I could do FSK (there is a really simple minor mod to make it work)

While AFSK would (still) work, the "real" RTTY users didn't do it that way.?? FSK isn't really "old fashioned", it' is the correct & accurate description of the mode.? AFSK is actually the "compromise" method of creating a frequency shifted signal.

It's also similar to the CW generated by a Collins KWM-2 or other S-Line transmitter.? They used an audio tone generator "through" the ssb balanced modulator to "generate" the CW.? The problem doing this is you're "tied" to the radio's opposite sideband? and carrier suppression specs (while adequate, it's not "perfect")?

AFSK does seem to work ok for today's appliances. The manufacturers have made it pretty simple to do RTTY.? My ICOM IC-705 has RTTY completely built in!? It's so easy now, there's not much point in even doing it!
--

73/Rick

WA6III
*Every post is created using Linux

 

Rick,
Yup, we were back in the dinosaur days too.

See attached photo of my dad at his (our family) station circa 1969.
Model 19 and model 14.? 75S-3B transceiving FSK with my dads homemade 32S-3, 1KW military xmtr (from MARS).

Computers and AFSK make it so much easier now a days!? Not to mention save a lot of paper, hi hi...
73,
Gary
WB6OGD

?

W6FFY.jpg

 

Now THAT's a groovy station!

Barry - N4BUQ

From: "wb6ogd" <garywinblad@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Wednesday, April 12, 2023 4:00:30 PM
Subject: Re: [DRAKE-RADIO] T4XC problem

Rick,
Yup, we were back in the dinosaur days too.

See attached photo of my dad at his (our family) station circa 1969.
Model 19 and model 14.? 75S-3B transceiving FSK with my dads homemade 32S-3, 1KW military xmtr (from MARS).

Computers and AFSK make it so much easier now a days!? Not to mention save a lot of paper, hi hi...
73,
Gary
WB6OGD

?
Rick WA6III
 

That is REAL Ham Radio!
--

73/Rick

WA6III
*Every post is created using Linux

 

I believe most modern transceivers have data FSK in/out lines. I know the Kenwood TS590 does. Not saying it is better but depending on the interface you are using it may very well be wired for FSK as well as AFSK. The only real drawback of AFSK is the spotting frequency is not correct while with FSK it is. There are various menu settings on the TS590 to control shift, polarity, etc. Some transceivers even decode the RTTY to the screen.
--
Doug, WA3DSP
 

Oh how I remember Gary's family shack...we went to high school/college together and I was always just overwhelmed and envious at the wonderful operating position they had...one reason I've always tried to emulate it! ?Great memories from the late 60's! ?73 - Dino KL?S (ex WB6FZN)

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