.... I'll explain that noise point:
In order to reduce the intrinsic resistance of the PIN diode, you have -
especially with the BIG high power ones- to pass about 200mA or more through
the receive diode in order to reach 1 ohms or so. With this amount of
current , the junction generates noise which can be seen to raise the noise
at the antenna terminal. In my job I had access to an HP noise figure meter
and found about 0.5 dB increases.
It really isn't much, when considering that an HF radio has a noise figure
of about 10 dB but it's there! In an average location you probably won't
notice it, but it's there.
It also introduces a few tenths of decibel loss (resistive) and that adds
directly to the noise figure of the receiver!
Overall you can expect about 0.8 to 1 dB degradation on receive and that
also what most of them are specified.
73, Alex
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of John/K4WJ
Sent: Wednesday, April 02, 2008 4:51 PM
To: 'amps'
Subject: Re: [Amps] Relays
I use a DEO QSK-1500 for my QSK operations. This is a PIN diode unit
that K8RR and W4TV designed back in the 80s. It was rather expensive
in those days but there are a few of them out there that can be
purchased in the $150 to $200 range. I have two QSK-1500 units, but
one needs repair.
I've discovered that some of the sellers are elderly and have abused
their units to the point that some repair is necessary. However, they
are very easy to trouble shoot and can be repaired rather cheaply
unless the main transmit PIN is damaged. Then it becomes a rather
huge task trying to locate one of these PINs. (It is rare for them to
be damaged.)
I did a poor job of matching my antennas to the transmission line so
I use a TenTec 238 to bring the SWR down to a level that doesn't
bother the QSK-1500. I use the QSK-1500 with a TenTec Omni VI Plus
and either a Ameritron ALS-600 or an old Alpha 77, which is currently
on the fritz.
One plus for using PIN diodes is that they are silent.
I have no idea what Alex is talking about when he mentions that they
operate as a noise diode. I can't tell the difference in the received
signal between having the QSK-1500 in the transmission path or
by-passed. I can copy the weakest DX signals. However, I've never
taken any noise measurements with the unit in or out of the receive
path, I'm only going by what my ears tell me.
I LOVE my QSK-1500s.
73..de John/K4WJ
At 02:41 AM 4/2/2008, Alex wrote:
>Hi guys:
>It so happens that during the last 2 years or so I worked on high power
>amplifiers in the kilowatt range .
>PIN diodes are made by very few manufacturers, coming and going all the
>time. They can run In the 300$ dollars range, are susceptible to burn out
at
>mediocre SWR,s and require back bias voltage approximately 3 times the PTP
>RF voltage involved. They also require a forward current of a few hundreds
>of mA to conduct well when open. This adds directly to the input noise
>because they operate as a noise diode would.
>In short, if you don't need fast switching speeds, don't mess with them.
>They also have only a poor isolation of around 30 dB. In QRO use the
>leftover power at the receiver port is still to much so that you need some
>additional switching after the main diode with associated driving circuits.
>In short, drop it!!!
>73 and all the best:
>Alex 4Z5KS
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>Behalf Of Kim Elmore
>Sent: Wednesday, April 02, 2008 4:48 AM
>To: amps
>Subject: Re: [Amps] Relays
>
>Thanks, Vic! Makes perfect sense. Yes, the PIN diodes are quite
>expensive, especially for ones capable of handling much power.
>
>73,
>
>Kim N5OP
>At 06:28 PM 4/1/2008, you wrote:
> >Kim Elmore wrote:
> >
> > > But, this does lead to a question: are PIN diodes avoided simply
> > > because using them is far more complex than relays, or is there some
> > > other reason they aren't often used?
> >
> >The cost of the diodes and associated circuitry is more than a cheap
> >relay. And they are susceptible to damage from lightning-created
>transients.
> >
> >I had an Alpha 86 with pin-diode switching that worked great. Never any
> >problems. But a lot of Alpha users did have problems and at some point
> >they started using vacuum relays. Someone who can afford a newer Alpha
> >can tell us if they still do!
> >--
> >73,
> >Vic, K2VCO
> >Fresno CA
> >http://www.qsl.net/k2vco
> >_______________________________________________
> >Amps mailing list
> >Amps@contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
>
>_______________________________________________
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73..de John/K4WJ
ex K8PXG 18 Jun 1959 to 11 Feb 1997
K8WJ 12 Feb 1997 to 08 Apr 1997
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