>
>> > 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
>> >
>> >
>> >________________________________________________________________
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>> >
>>
>>
>> Rich, AG6K, 805-386-3734, www.vcnet.com/measures
>
Rich, AG6K, 805-386-3734, www.vcnet.com/measures
|