A builder of my circuit wrote:
>Hi Tony. Thanx for the new circuit. I used 2N2222's throughout and
>am having difficulty getting it to work. Perf board construction
>is for the birds as I've found numerous soldering probs both logical
>and simply too much solder.
I hope you didn't use all NPN's! The 2N3906 is a PNP transistor and cannot
be substituted for a 2N2222.
>I also find that the xmtr goes into xmit upon cold boot, not on
>a software, 3 finger salute, or push button reset but just when
>I first turn on the computer.
>
>I can't get the PTT to work. BTW, I'm doing this on an FT-1000D,
>and I find 13.5VDC on the PTT line and it can't be sunk to gnd
>by the PTT xsistor. I haven't tried a pull-down resistor yet,
>but will try that next.
Try pulling the PTT to ground with a current meter and we'll see if the
little 2N3904 can do it. You may just have to use a smaller resistor
in the base to give it enough output current.
>I'm also getting hum on both playback & record audio only when
>the Mic Input of the SB is connected. When I disconnect it its fine.
>Do you bring both channels (stereo connectors) for the playback
Yes.
>and record/Mic In lines?
No. CVB seems to record in the monoaural mode.
>Have you experienced hum or RF feedback problems?
Not after I grounded the PC and rig together with a fat hunk of grounding braid.
> Any advice on getting a clean playback?
I am reminded of the four "rules of VHF construction":
1. Ground everything in sight.
2. If it can't be grounded, bypass it.
3. If it can't be grounded or bypassed, sheild it.
4. If it can't be grounded, bypassed, or sheilded, forget it.
>On the FT-1000, there is +9VDC at pin 4 of the DVS DIN plug, not
>12V as you have on the 990. I'm not sure if this is a possible
>cause for my woes.
You may have to increase the base current to pull the lines low. Check with
a voltmeter to see if the PNPs are pulling the lines down to within 1 volt
of ground. They are just the inputs of a 8255 MOS IC, so that is low
enough. If not, decrease the 330 ohm resistors to 100 ohm.
AE0M, Tony Becker - becker@shell.portal.com - Silicon Valley, U.S.A.
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