[DSP-10] SR105 diode question

[Bozidar Benc]

Bob,

Thanks a lot for the reply.

I've read that text a while ago, but then forgot about it. :-)

BTW, I'm very surprised how building this kit goes smoothly. With good
tools, soldering SMD components is faster and easier than soldering
through-the-hole components.
I hope I'll do the first smoke test tomorrow. :-)

73, Bole, 9A3RR


> Hi Bole,
>
> I just finished building my DSP-10 and had the same problem the
> documentation does not show the location of the diode. I decided that it
> is best for mechanical stability as the leads of the diode are heavy to
> solder the cathode to the center lead of Q106 gate (which is connected to
> Q104 collector) and the anode to the right side of R131 that is connected
> to R130 this connects for Q103 Base.
>
> The information below was obtained from
> http://www.proaxis.com/~boblark/dsp10.htm
>
> "SR105" Diode When the DSP program is first started and before the PC
> program is run, the DSP-10 can come up with BOTH transmit and receive
> turned on. This sets up a loop that oscillates at full power! Very bad.
> My DSP-10 shows about +16 or +17 dBm out. The happens because the shift
> registers (U107, U108) come up uninitialized. The eventual solution will
> be to program an EPROM that includes the setting of the shift registers
> at DSP startup. Here is a work-around until you have an EPROM version:
> Acquire a Schottky diode and solder the cathode (bar end) to the junction
> of R132 and Q104-collector. Solder the anode (non-bar) end to the
> junction of R130 & R131 (base of Q103). It must be a low barrier voltage
> diode like the Schottky, but it can be either a rectifier or small-signal
> type. I used a SR105 from Digi-Key, but I notice that Radio Shack has
> 1N5817-1N5819 or 1N5820-1N5822 on special order status. W7LHL suggested
> that a 1N34 type of germanium could work also. This work-around prevents
> the 'transmit' from being enabled when 'receive' is enabled. (Added 5
> Sept
> 01, based on 27 Jan 00 reflector posting.)
>
> 73,
> GL
>
> Bob Johansen WB2SRF
>
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