In article <4dub0i$12t@florence.scotnet.co.uk> GW0ACH@lordjohn.celtic.co.uk (L
ord John) writes:
>Does anyone know if there are any mods for the IC706 especially one
>for extended receive transmit. I would particularly like to be able to
>use the rig on 70MHz and  27MHz

Removing D59 and resetting the processor will open up transmit for
HF through 60 MHz. I don't know the regulations in your lordship's
country, but here in the States use of this radio over the air on 
27 MHz would be forbidden since the radio is not type accepted for 
that service. (Driving a transverter with it would be fine however.)

There is no known mod to allow transmit on 70 MHz as yet. There are a 
number of people trying to get expanded VHF transmit coverage from the 
unit, but no one seems to have found the right combination to make that 
happen, and it looks like that if anyone does it will only open it up 
for 118 MHz to 172 MHz, and not the 70 MHz band. That's because T8 is 
only asserted in the 118-172 area of VHF, T8 controls the TR relay. 
(Note, most uses, aside from MARS/CAP, of the unit over that range 
would also be forbidden under US rules, yours may be different.)

The radio is an interesting puzzle, but I don't intend to leave any
out of amateur band transmit mods in mine after I finish exploring
the puzzle. I don't want the possibility of accidentally transmitting 
out of band to exist in the radio, and I certainly wouldn't condone 
deliberate transmission out of band. 

I am concerned about better out of band reception, however. There 
is the so called yellow wire mod which improves VHF reception 
somewhat outside the 2 meter amateur band, but that mod doesn't 
give the full coverage the radio is capable of supplying. I've 
discovered a change to the 60-200 MHz bandpass filter that
offers a marked improvement in sensitivity across that range, but
I've been cautioned that it may make the radio very susceptable
to intermod when used on 2 meters. So far I haven't experienced
this (I'm in a suburban area not overly plagued with strong
pager transmitters), but a bit of caution is advised until this 
is researched more carefully. 

It appears that any problem of this nature would be the result of 
excessive leakage signals around D6 and D7, the bandpass filter 
switching diodes. It should be possible to solve that, perhaps by 
driving the switches harder via a resistor change, or by using
diodes with better isolation characteristics. I'm refurbishing 
an old General Radio unit oscillator to serve as a pager simulator 
to test this theory.

Gary
-- 
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
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