Subject: Icom IC-706 Extended RX mod
From: pjka@kanto.cc.jyu.fi (Pertti Karppinen)


Here's the mod I promised for You (it can be found with a
picture pointing out the capcitors at 
http://www.jyu.fi/~pjka/IC-706/ic-706rx.html):
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                         Icom IC-706 Extended RX mod
                                 From OH6LGM
Disclaimer:

I'm not responsible for any damage that may result following these
instructions. Remember also, that this modification voids Your warranty.
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Icom 706 doesn't out of stock listen to frequencies over 148MHz, although
that is advertised. At Least mine didn't.

Studying the schematics I noticed a front-end filter, that should be
operating in the range of 60MHz - 200MHz. I studied the filter with a
program and noticed, that the passband was 60MHz - 140MHz !! The upper end
was blocked out.

I changed the circuit in a way that enables the radio to work as advertised
by removing Capacitors C53 and C153. Now the filters upper edge is around
230MHz.

This modification doesn't affect 2m RX in anyway, because 2m has its' own,
thight front-end, that is used instead of the modified filter, when in 2m
band. HF and 6m aren't affected either.

The Capacitors are found in the PA UNIT board, behind the external speaker
connector in a relatively easy place.

The job requires cautiousness because the components dislike static and
excessive heat.

This modification works, if the radio isn't already modified with the
modification, which puts 2m front-end in use in frequencies above 144MHz.

At Least My unit worked well with this modification.
Measured from my IC-706:
Frequency                Sensitivity (microvolts /20dB SINAD)
60-140                   0.14
144-148                  0.12
150                      0.18
155                      0.15
160                      0.2
165                      0.3
170                      0.4
175                      0.6
180                      1.5
185                      1.5
190                      >100mV -- deaf!
195                      5
200                      29

OH6LGM@OH6RBW.#JKL.FIN.EU
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--
\begin{stquote}
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Because you are intelligent, wise and quite correct.
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--
|Pertti Karppinen, Student of Computer Science,           |'Bridge Players |
|Mathematics department, University of Jyvaskyla, Finland |      Do        |
|Email: pjka@jyu.fi URL: http://www.jyu.fi/~pjka/         |      It        |
|HAM: OH6KTR QTH: KP22UF                                  | on the Table'  |