IC451.1


        LOW NOISE FRONT END FOR ICOM IC-451
        
A very simple mod, no re-aligning necessary, more gain, lower noise, cheap to
do.
The front-end transistor on the ICOM-451E is a fairly noisy 3SK48. This mod
replaces it with a BF981; results are very much better and avoid the need for
(and cross mod due to) a preamp.
Select a "standard" signal, e.g. a repeater, which is fairly predictable, and
strong enough without being too strong; say S6 or so. Remember that strength.
Disconnect mains lead. Remove top cover. Remove all plugs on left hand board
(rig is front towards you). Remove the board. Locate Q9, a TO-18 can soldered
between two R.F. transformer cans. Unsolder it; you may need two irons for
this. On the underside of the board, solder the new device in. The long lead
points away from the input socket, and the device has the part number visible
through the hole left by the old FET. Some shortening of leads will be
necessary. Replace board, connect all (ALL) plugs, reconnect mains, try rig
out.
1) If any problem has occurred, disconnect mains and look for wrong FET
   connection and/or solder short - its small in there!
2) If all is well, rig appears slightly noisier, but signals are much
   stronger. Try your reference signal. It should be noticably higher on the
   S meter.
3) If you feel that you must, tweak the cores of the adjacent filters. Only
   the adjacent ones, and don't move them far.
Finally, you should get a gain improvement of around 10dB (estimated) with a
reduction in noise figure to about 2.5dB overall.
73 Peter G8EUX