[Packet] DCD on MFJ-1270B

[Doug Laidlaw]

Thanks for your further reply Jerry.  I seem to have deleted it, but 
fortunately I printed it out first.

I did have both the rig and the TNC running off the same power supply, but 
switching the TNC to a plugpack made no difference.

I am not the most delicate at soldering, so I inserted a small 1:1 audio 
coupling transformer into the audio line to break the earth loop.  That did 
the trick.  The DCD  LED comes on only over a narrow range of the volume 
control, and I can receive packets.  Thanks again for your help and 73,

Doug VK3KDI.

On Monday 18 March 2002 3:37 pm, you wrote:
> The demodulator input is sensitive to a few millivolts or less. It may
> be that your squelched radio puts out more than that to an open circuit.
> You might try a speaker terminating 4 to 8 ohm resistor, or even a 10 or
> 20 dB attenuator between the radio speaker connector and the TNC. There
> is a DCD mod kit that requires coherent data to be activated. It may
> have some adjustment possible, but shouldn't detect DCD on anything but
> a true data signal.
>
> Part of the DCD mod that is worth while even without the DCD circuit
> board is removing the MF-10 from the demodulator. It was added to
> compensate for a poor frequency response in some radios but causes more
> problems by saturating from excess gain than it solves. Removing the
> MF-10 requires added a capacitor to couple the input audio past it. Its
> been so long since I last did that, that I don't remember the precise
> details, but I could probably find them if I dug deep enough in my
> documents.
>
> 73, Jerry, K0CQ