Oh, you are absolutely correct.
PIN diodes definitely have their place in our hobby, but some people highly
overestimate what all they can do.
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 7:00 PM
To: rick@dj0ip.de
Cc: 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] QSK switching diodes in Scout
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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> >
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