I use a pin diode switch at the antenna to switch the pre-amp in and out
during TX and RX cycles. I supply RF (lots of it) and 12VDC. This is in
a 50 ohm VHF circuit running "legal limit" so to speak. The preamp has a nf
of something like 0.3dB and a gain of 20 dB.
I don't see the problem or concern in a 50 ohm application. As to switching
at a PA Z.......forget it.
73
Bob, K4TAX
----- Original Message -----
From: "2" <2@vc.net>
To: "Steve Katz" <stevek@jmr.com>; "Mark" <wb8jkr@juno.com>; "AMPS"
<amps@contesting.com>
Cc: <on4kj@skynet.be>; "AMPS" <amps@contesting.com>
Sent: Thursday, June 19, 2003 11:07 AM
Subject: RE: [Amps] electronic switching
> >
> >> > One problem with PIN's is if the RF voltage
> >> >the PIN is subjected to in its "off" state exceeds the
> >> >bias applied to the PIN to turn it off, the RF voltage will
> >> >attemp to turn the PIN back on.
> >> > In the limited ampunt of PIN diode work I've done here
> >> >it seems the PIN "off bias" should be at least twice the
> >> >applied RF voltage if any sort of SWR may be
> >> >present. So in a 50 ohm circuit at 1500 watts you'd need
> >> >about 5-600 volts reverse bias.
> >>
> >> ** 1500W into 50-ohms =s c. 775v p-p. To prevent a PIN diode from
> >> conducting at any point during the cycle, at least 800v of reverse bias
> >> is needed, provided the SWR was 1 to 1, otherwise the PIN diode could
> >> short.
> >>
> > //Guys, this doesn't really happen. You only need to reverse bias the
PIN
> > when it is intentionally switched OFF, for isolation.
>
> **
> As seen on an oscilloscope, with 1500W-pep into 50-ohms, the peak to peak
> V measures a bit over 750v.
> - There is more than one PIN diode in a T/R switch. During receive, one
> of the PIN diodes connects the transceiver to the antenna jack. During
> transmit, this PIN diode must isolate the transceiver from the antenna
> jack of the amplifier . In order to do this, it would seem that enough V
> to keep this PIN diode reverse biased at all points on the 775V-peak to
> peak sinewave is needed. Is this not so?
>
> >When a PIN is
> > switched ON, to pass RF current, it only requires forward biasing
CURRENT,
> > which doesn't take a lot of voltage. Remember, due to the intrinsic
layer
> > between the P and N materials, this is a device that behaves as a
> > current-controlled resistor, not a rectifier. It is true that a PIN in
> > its OFF state must be reverse biased with more DC voltage than the RF
> > envelope peak it is trying to block, which is problematical for very
high
> > power applications....but then, I'm not sure where the "10KW" and beyond
> > discussion started. Because a properly biased PIN is very linear, they
> > are also commonly used as low-distortion modulators and
current-controlled
> > attenuators in L, T and pi configurations.....WB2WIK/6
> >>
> >>
> >>
> >> >. In a Hi-Z cicuit such
> >> >as a plate tank I.E. 2000 ohms, you'd need about 3500 volts.
> >> >Thats a tall order.
> >> >
> >> ** indeed, Mark.
> >> >
> >> >
> >> >On Wed, 18 Jun 03 13:10:12 -0700 2 <2@vc.net> writes:
> >> >> >Hi Rich,
> >> >> >
> >> >> >PINs are readily available to 1000Vpk and of course can be placed
> >> >> in series
> >> >> >for higher voltage applications.
> >> >>
> >> >> ** Hello, Steve -- For 10kW @ 50-ohms, a minimum piv of 2000v is
> >> >> needed.
> >> >>
> >> >> >Remember, a PIN is not a P-N junction
> >> >> >device and doesn't really have a "PIV" rating...when biased OFF,
> >> >> its a large
> >> >> >value resistor and when biased ON, it's a small value
> >> >> resistor....using
> >> >> >power devices that can be biased ON with amperes of current, that
> >> >> resistor
> >> >> >can become *really* small......-WB2WIK/6
> >> >> >
> >> >> >"Success is the ability to go from failure to failure with no loss
> >> >> of
> >> >> >enthusiasm." -Winston Churchill
> >> >> >
> >> >> >> -----Original Message-----
> >> >> >> From: 2 [SMTP:2@vc.net]
> >> >> >> Sent: Tuesday, June 17, 2003 7:15 AM
> >> >> >> To: Dr. William J. Schmidt, II; on4kj; AMPS
> >> >> >> Subject: Re: [Amps] electronic switching
> >> >> >>
> >> >> >> >Well, we do..... there are diodes that will handle as much as
> >> >> 10kW....
> >> >> >> but
> >> >> >> >they are expensive. Harris uses them in their gear...
> >> >> >> >
> >> >> >> ** What is the piv rating of such diodes, William?
> >> >> >>
> >> >> >> >Sincerely,
> >> >> >> >
> >> >> >> >Dr. William J. Schmidt, II K9HZ
> >> >> >> >
> >> >> >> >"Collector of Edison Wind-up Phonographs... Do you have one for
> >> >> me?"
> >> >> >> >Email: bill@wjschmidt.com
> >> >> >> >Alternate Email: wmschmidt@charter.net
> >> >> >> >WebPage: www.wjschmidt.com
> >> >> >> >
> >> >> >> >
> >> >> >> >
> >> >> >> >----- Original Message -----
> >> >> >> >From: "on4kj" <on4kj@skynet.be>
> >> >> >> >To: <amps@contesting.com>
> >> >> >> >Sent: Sunday, June 15, 2003 2:44 PM
> >> >> >> >Subject: [Amps] electronic switching
> >> >> >> >
> >> >> >> >
> >> >> >> >> Hello Folks,
> >> >> >> >>
> >> >> >> >> About steatite wafers used for band switching.
> >> >> >> >> Why dont we see switching systems based on pindiode, for input
> >> >> ( 100 w
> >> >> >> )
> >> >> >> >> must be possible nowadays. Even for high output power !!
> >> >> >> >> What say ?
> >> >> >> >>
> >> >> >> >> Jos on4kj
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> ----- Original Message -----
> >> >> >> >> From: "Osten B Magnusson" <sm5dqc@algonet.se>
> >> >> >> >> To: <amps@contesting.com>
> >> >> >> >> Sent: Saturday, June 14, 2003 10:35 AM
> >> >> >> >> Subject: [Amps] 572B's WARNING
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> >
> >> >> >> >> > STAY AWAY FROM RICHARDSON ELECTRONICS, ENGLAND
> >> >> www.rell.com
> >> >> >> >> >
> >> >> >> >> > 572B's are sold here in Europe by different dealers, the
> >> >> tubes are
> >> >> >> >> distributed by Richardson Electronics in England, and they
> >> >> claim that
> >> >> >> it's
> >> >> >> >> Cetron tubes manufactured for National. Sorry to tell, but it
> >> >> isn't the
> >> >> >> >> truth - it's newly produced Chinese tubes re-badged by
> >> >> Richardsons as
> >> >> >> >> National and also have ''Made in USA'' printed on them. So be
> >> >> careful,
> >> >> >> >> before buying. I have been offered, not by Richardsons, but by
> >> >> the
> >> >> >> >> distributor to get a full refund if sending the tubes back.
> >> >> Richardsons
> >> >> >> >does
> >> >> >> >> not even answer e-mails...
> >> >> >> >> >
> >> >> >> >> > This is part of an e-mail from a serious distributor in
> >> >> England:
> >> >> >> >> >
> >> >> >> >> > >>Hello Osten,
> >> >> >> >> > >>Taylor is a brand name for RF parts but these can be
> >> >> re-badged
> >> >> >> >any
> >> >> >> >> type!
> >> >> >> >> > >>We have National 572B which are badged by Richardsons
> >> >> which is
> >> >> >> >the
> >> >> >> >> main
> >> >> >> >> > >>outlet for Eimac, but need not be Eimac !
> >> >> >> >> >
> >> >> >> >> > There are original Cetron NOS 572B's available here in
> >> >> Europe, have a
> >> >> >> >look
> >> >> >> >> at www.clhi-fi.it It's in Italian, but click on
> >> >> ''Surplus'' and
> >> >> >> than
> >> >> >> >> ''avanti'' to go to page four. There are no prices on the WEB,
> >> >> but in
> >> >> >> an
> >> >> >> >> e-mail they asked 500 ''euros'' for a matched pair, plus
> >> >> postage.
> >> >> >> That's
> >> >> >> >> totally USD 645 for a matched pair!!! I know that there are
> >> >> also NOS
> >> >> >> >> Cetron 572B's available in USA, but unfortunately we have to
> >> >> pay more
> >> >> >> >> postage, customs, 25 percent VAT etc. so here we always try to
> >> >> buy from
> >> >> >> a
> >> >> >> >> European Community country, this was no customs and other
> >> >> extra charges
> >> >> >> to
> >> >> >> >> pay.
> >> >> >> >> >
> >> >> >> >> > Probably time to get all ''glass tubes'' amplifiers marked
> >> >> ''junk''
> >> >> >> and
> >> >> >> >in
> >> >> >> >> the future only get amplifiers with ceramic tubes!
> >> >> >> >> >
> >> >> >> >> > 73 de Osten SM5DQC e-mail: sm5dqc@algonet.se
> >> >
> >> >
> >> >________________________________________________________________
> >> >The best thing to hit the internet in years - Juno SpeedBand!
> >> >Surf the web up to FIVE TIMES FASTER!
> >> >Only $14.95/ month - visit www.juno.com to sign up today!
> >> >
> >>
> >>
> >> Rich, AG6K, 805-386-3734, www.vcnet.com/measures
> >
>
>
> Rich, AG6K, 805-386-3734, www.vcnet.com/measures
>
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