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FT-847 frequency drift fix



Hi,

Many have noted the tendency of the FT-847 to drift excessively, especially
during transmitting periods.  OZ1PIF came up with a simple and cheap
modification which dramatically improves the situation.  It involves
attaching a simple thermostatically controlled heater to the main xtal, and
insulating it from the cooling fan draft.  You can see the mod at
http://home24.inet.tele.dk/oz1pif/QH40A.htm and order the QH40A directly
from Kuhn http://www.kuhne-electronic.de/english/special/crystalheater.htm
or SSB Electronics at http://www.ssbusa.com/  I got mine from Kuhne
directly, promptly, and no hassle.

The working voltage range is given as 8-12 volts, and I installed mine using
the 8 volt regulated buss.  There is a MUCH easier way to make the
connections than OZ1PF used.  Message me off list if interested.

Gene, W4IMT, who is longtime AMSAT member, but not very active on the birds
these days, attached his to the 13.8 volt FT-847 input, before the power
switching.  As he uses the PS for other parts of his station, it is usually
on, and means there is no warm up period.  It has tolerated the 13.8 volt
for many months with no smoke.  I got the following report which has some
quantitative data.

====================================

One of the local hams, who lives about ten miles north, and I have 
been experimenting with Chip64.  First we wanted to learn to use the 
program by QSOing on 2 meter SSB.  (HF QSOs are hard to find.  So far 
none.)  I noticed a stable line on the receive waterfall and when I 
finished transmitting it would drift about 20 Hz.  No problem here, 
but it is a chance to measure the warm up characteristic.

Our room temp in the mornings is about 65 F.  Recall my xtal heater 
is wired in front of the power switch.  With the power on for a long 
time before turning on the radio, the drift is smooth and about 40 
Hz.  Time: about one minute.  Not bad at all!  But if the power 
supply is off overnight and I turn it and the radio on at once, the 
drift is an S shape and changes about 250 Hz in 2-3 minutes.

So  the xtal heater really does a nice job.

====================================

I have no financial interest here, but wanted to pass along a nice way to
improve the rig's performance.  It is not as good as an oven, or a
GPS-locked standard, but considering the cost and simplicity you get a lot
of bang for the buck.  I ordered a few, all of which are going into things
like my mode-L TX converter, and possibly the mode-S RX converter.  (The
knuckleheads soldered the xtal case directly to the PC board to provide a
heat sink!)

Alan
WA4SCA
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