Date: Wed, 24 Feb 2010 11:06:16 -0500
From: Paul Gerhardt <phgerhardt@gmail.com>
Subject: Re: [Amps] TX Inhibit on MK-V
Jim thanks for your write up on the Tx Inhibit.
I made a cable using the Acom link below but and the QSK worked fine with my
Alpha 78 but the TX Inhibit did not 'come on' when I plugged the din in. I
had the rig delay set on 20 which seemed to be more than enough.
A lister from the 'MP' list also said that the TX Inhibit does not work!
RE: [FT-1000MP] Re: QSK interface
"At least on the Mark-V, the transmit inhibit does not work even though
the manual say it does. Others have tried and found the same condition.
## here's the scenario. The MK-V has TWO internal resistor's in series,
with that TX inhibit lead. [ forget the values] With a SOLID + 12 vdc
applied to inhibit lead, there is now 7 vdc dropped across 'R1'... and
5vdc dropped across..'R2'. The 5 vdc across 'R2' is then applied
further downstream to do the actual inhibit.
### When a 10 k pull up resistor is used to apply +13.8 vdc to the din
pin, now u have THREE resistor's in series, and of course the 10k has a big
v drop across it, leaving very little left for... 'R2'.
## The fix is to reduce the 10K... down in value... like to 1K, then the TX
WILL be inhibited. With the external grnd applied to the inhibit lead,
now RF will flow. 13.8 / 1000 = .0138 A... or 13.8 Ma = .19 W
### Even with a 500 ohm pull up resistor.. 13.8 /500 =.0276A ..
or 27 ma ... = .38 w
### Clearly 10 k is way too high in value. On the last amp I designed
for a buddy, we used a sped up RJ1-A on the input side of the amp,
and 2 x paralleled [sped up] RJ2B's on output side, + a sped up RJ1-A
for the 100 k cut off bias. It was crucial that the TX inhibit lead actually
works on that amp. Since the input relay is way faster [1.8 msec]
than the slower output relays, [8-9 msec], we used a custom built
external 12 msec delay circuit, in conjunction with the TX inhibit lead.
## It runs flawless. NO qsk, but no hot switching. Smooth fast VOX
cw and ssb.
Alternative:
Check the closing time for the Alpha because they are fast. My 91B is
ready in 2ms (high speed vacuum relays with high voltage close and low
voltage hold). The Mark-V doesn't put RF out until 7-8ms after PTT
output is initiated leaving 5-6ms head room.
## I mentioned this B4. IF the vac relay's in ur amp are FAST..
like 2msec, you don't require the TX inhibit lead function at all
in the MK-V. We use it simply cuz the G2 / RJ2-B/C 's are slow
to begin with [15-18 msecs]... and when sped up, are still only
8-9 msec. That ends up a mess [total disaster if a 1.8 msec relay
used on input]
The folks at Alpha can tell you the closing time if you can't measure it
yourself.
To measure it I used a dual trace 100MHz digital storage scope looking
at the Mark-V's TX-GND jack and the Alpha's output relay.
### You mean the yaesu DIN TX-Gnd....and not the RCA TX-Grnd?
The RCA TX grnd, is via the real slow SPST yaesu mech relay...15 msec
## If it was via the RCA TX jack, then yaesu has used a super fast spst
mech relay. Lemme know if this is the case, since my MK-V's are slow.
The 1000/D is also slow.. 15 msec. Yaesu could have changed to a
faster spst mech relay, during the course of production.
later.... Jim VE7RF
73,
Bob - W6OPO"
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