Subject: TW4000 mod notes
I just looked over schematics for the Kenwood TW-4000-A/T/W dual bander (yes,
I'm actually doing the schematics I've received - but I have a couple of BIG
boxes full, so be patient if yours is in there!), and it looks like a very
good candidate for 9600 baud. Filters look good, although digitally optimized
filters such as MuRata SFG-455D or SFH-455D would allow a tighter passband; and
it uses a separate transmit oscillator common to both 144 and 430 MHz for
generating FM. This uses a crystal, inductor, and varactor to produce nice,
linear FM, and heterodynes up from there to the respective bands. This is
exactly as I've described in my 9600 baud manual as the "ideal" 9600 rig.
The "mods" I've come up with are:
TXA:Tack a 6.8k resistor to the cathode of D-16 (junction of C125-R95-D16)
RXA:Tack a 4.7k resistor to IC-1 pin 17
If the received eye pattern from a known good transmitter is jittery, try
changing C-155 (associated with Q19) from .01 to something like .005 - .001.
It also might be necessary to change C125 from .0022 to .001 if the transmit
waveform is jittery.
I've not tested this, so would appreciate feedback from anyone trying this.
So far, I've received precious little in the way of feedback, so I have no
idea whether these mods work or not.
73, Mike Curtis wd6ehr
SOURCE: The QRZ Windows Ham Radio CDROM |
