Subject: W8JI FT1000D Key Click Mod-My Experience
To: <topband@contesting.com>
Date: Fri, 20 Jun 2003 10:12:54 -0700
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Many of you might be interested in what I found while doing this keying mod.
When the transceiver is in receive, there is -8.13 VDC on Pin 2 of J3024.
This comes from J2008 pin 4 on the IF board and turns off diode D3009. This
means there is negative voltage on C3243 which is a 1.0uF electrolytic cap.
Don't know how that escaped the engineers in the initial design but when I
measured the
cap it still read 0.85uF. Anyway, I replaced it with a monolithic 1.0uF cap
just to be safe. At key down the voltage at pin 2 of J 3024 goes to +7.9 VDC.
I installed the mod on a small copper clad board using a 15K resistor, a 1uF
monolithic cap, and a MMBT3904 (all surface mount) instead of the 1.5K and
10uF electrolytic that was originally called out. I turned on the rig and
sent a series of dits about 50 WPM into a 150 watt, 30 db attenuator that
was followed by a crystal detector.
The detected RF showed a total risetime of about 10 mS and a fall time of 3
mS on
the scope. I went back and changed the 15K to a 7.5K and the risetime
now measured about 5 mS and the fall time was 3 mS. I stopped there as I
thought 5 mS and 3 mS were good enough. (The original risetime was about 10
uS! This mod does not seem to affect the fall time of the keying waveform.)
Since I had to remove the audio board to change C3243, I placed the board
next to C3243. There is plenty of room for it without having to clip the
wire on the J3024 connector.
I have not done the bandwidth test yet. I only wish I had a digital scope
so I could
record and post the waveforms.
73 Hardy N7RT
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