Alinco DX-70 - some more mod ideas...
Joseph Fitter BV/N0IAT
Been happily using the Alinco DX-70 HF + 6 rig for about 6 months now.
Having even run it in a major contest as a spotting rig, I can safely
say that it is holding it's own (with 6 months of guarantee remaining).
I have made all the original wide-band mods, and have been satisfied with
the expanded VHF-low band receive. Additionally, I am surprised at the
sensitivity down in the "lowfer" end of the band. It does a nice job
down there, though synthesizer noise is a bit higher than desired.
Here are some other "mods" that I've done on my rig -- perhaps others out
here in virtual radio world have similar or improved ideas on how to get
the most out of these super little rigs.
1. I found an MFJ CW keyer, based on the infamous curtis 8044abm chip
at a local ham shop. The keyer is designed to be internally mounted
in one of the MFJ QRP rigs. As such, the board for the keyer is
quite tiny. The keyer also seems to work fine on 13.8 VDC which is
a natural match to any mobile power source.
I managed to replace the "speed" pot on the small keyer with a low
profile screwdriver settable circuit board
mountable pot. I also removed the molex power / key connector
jack to save additional room. The resulting circuit board is now
very thin and compact...enough so to mount directly inside the DX70
case. I ran the keyer wires out one of the heatsink holes, and used
a small 3 conductor phono jack for "paddle input". The jack is
connected to the rear heat sink via a small metal "L" bracket and
tiny self-tapping sheet metal screw. I can access the "speed"
control for the keyer thru the bottom side of the chassis near the
ctcss switch bank. I use a "diddle stick" to adjust speed if needed.
While not totally convenient to adjust speed, I ususally leave it at
about 25 WPM and all is fine.
Power is tapped from the "atu" tuner molex plug, from the inside of
the radio to the keyer. I measure about 40 milliamps at 13.8 VDC,
so very little current is required and full funcitonality of the
ATU mechanism should be possible.
2. QSK improvements. Like the IC-706, something HAD to be done to
improve the QSK performance. The relay inside was far too loud.
I have experimented with a reed relay (quiet, high speed) but could
not find one that handles the current. So far anyway, but I have
ordered some higher current reed relays and hope this fixes the QSK.
The relays used only lasted about 3 days each...but did improve
QSK performance up to 45 WPM with great results. The switching
circuitry can handle the speed...just not the TR relay!
3. Filter improvement. I notice the narrow filters are Murata filters.
I have ordered some replacement filters with deeper skirts from
Murata and plan to install them once they arrive. This is some
tricky soldering for a layman like me -- but it's worth a try. The
stock filters are really quite good (for being free and included). I
was insterested in getting 250 Hz CW selectivity. If I cant find
the right filter combination, I suppose DSP is another option.
4. Speaker / Headphones audio. Thanks to a tip from Scott NF3I, I have
found a 1K resistor across the 'phones jack improves the audio
of my "el cheapo" stereo walkman headphones. This eliminates the
annoying low-level audio hiss that is present at very low volume
levels.
5. Cooling: A small low-profile 13.8vdc muffin fan mounted atop the
chassis just above the heatsink "holes" keeps things very cool. In
fact, the fan seldom runs in high speed now since the external fan
is forcing plenty of air onto the heatsink. This was not
necessary, but nice insurance at any rate. Power for the fan is
tapped via the 4 pin ATU molex connector (from the outside) since
I dont have an auto tuner for this rig.
If anyone has figured out how to unlock the receive any further I would
be interested in hearing more. Someone said VHF hi band could be
unlocked too....have not confirmed this or hear any more on the subject.
Thats all for now. Anyone have other ideas? I'd be interested to know
them !
73
Joe
BV/N0IAT Taipei TAIWAN R.O.C.