Point taken. However, as surprising of a performer as it is, I don't think the
Scout classifies as a "competition grade" rig and thus wouldn't be likely to
end up in a multi-multi operation, so the issue is academic in this case ;-)
73, Al
On Tue May 17 2016 12:38:17 am rick@dj0ip.de wrote:
> Clifton never worked as an operator in a multi-multi contest station! ;-)
>
> His description is accurate when describing how it responds to a wanted
> signal.
> However the voltage hitting the diodes will come from the sum of all
> signals hitting the front end of the radio.
> At a multi-multi station, you have 6 stations running 1500w in close
> proximity of each other. In fact it is sometimes 12 (considering you have a
> Run and a S&P on each band). There can be a lot of RF in the air, most of
> the time.
> This can cause these diodes to slightly forward bias, which in turn causes
> IMD in the receiver.
>
> Most people will never find themselves in this situation, so it is pretty
> much a non-issue for most.
> Our contest club tries to avoid radios and amplifiers with pin diode
> switching.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt, Germany)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Al Gulseth
> Sent: Tuesday, May 17, 2016 4:11 AM
> To: tentec@contesting.com
> Cc: Gary J FollettDukes HiFi
> Subject: Re: [TenTec] QSK switching diodes in Scout
>
> Clifton Labs has a writeup which might be of interest in this regard:
>
> <snip> It's commonly understood that the 1N4007 has an special junction
> structure resembling a PIN diode and it has, of course, been widely used as
> a "poor man's PIN diode" in RF power switching. Elecraft, for example, uses
> 1N4007 diodes for transmit/receive switching in both its 10 watt and 100
> watt option K2 transceiver.
>
> Used as a quasi-PIN diode for RF power switching, the 1N4007 takes
> advantage of the lengthy reverse recovery period, which prevents it from
> rectifying the high frequency signal it is switching. (This is because the
> reverse voltage half-cycle period of, say, a 3.5 MHz signal is much shorter
> (140 ns) than the reverse recovery time. Hence, if forward biased with DC,
> any reverse bias from RF negative half-cycles don't last long enough to
> neutralize the 1N4007's excess minority carriers. Hence, the 1N4007 stays
> forward biased and presents a low impedance to the full RF cycle. There's a
> minimum frequency for this effect which we see from the trace below. With a
> bias current in the
> 60 mA range from the 8012B pulse generator, we see the following voltage
> waveform. <snip>
>
> http://www.cliftonlaboratories.com/diode_turn-on_time.htm
>
> 73, Al
>
> On Mon May 16 2016 8:59:45 pm Gary J FollettDukes HiFi wrote:
> > Interesting, i did not know that!
> >
> > Thanks!
> >
> > > On May 16, 2016, at 6:28 PM, Stuart Rohre <rohre@arlut.utexas.edu>
>
> wrote:
> > > The silicon diodes signal path in the Scout are made with die
> > > similar to PIN diodes, or identical.
> > >
> > > -Stuart Rohre
> > > K5KVH
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