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Author Topic: Receiver Protection  (Read 33129 times)
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Pete, WA2CWA
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CQ CQ CONTEST


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« Reply #50 on: September 10, 2012, 12:10:19 AM »

germanium diodes are useless. A good ESD hit will take them out.

Gee, I've been using useless things for 40 years and never lost the front-end of a receiver.  I must be doing something wrong although I have seen one of #47 bulbs flicker during a winter snow storm. I better defer to the pin diode experts.
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
WA1GFZ
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« Reply #51 on: September 10, 2012, 09:05:09 AM »

No airplane in the sky uses piss ant 1n34s or light bulbs for ESD or lightning protection because they are skroteless.
Trust me we test this kind of stuff all the time and have real protection methods rather than JSes
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W3RSW
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Rick & "Roosevelt"


« Reply #52 on: September 10, 2012, 12:59:02 PM »

What do you use in a typical airplane box Frank?
Is it something like this that you mentioned earlier?
Quote
Go to ebay and search on 4X4RB Baruch is selling some nice power pin diodes he removed from boards. You don't bias diodes on because they will load the signal. You back bias them both positive and negative so they clip when the sidnal increases above the bias plus junction voltage. Racal used a nice Microwave Associates diode in many receivers. I think the Trr was around 2us. Not sure if you can still buy them. 1N3379 I think was the HP part but they are low power
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RICK  *W3RSW*
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« Reply #53 on: September 10, 2012, 01:06:56 PM »

Biased transorbes isolated by a fast diodes works very well. The fast diode is reverse biased just below the transorb conduction point. The reverse biased diode adds very little C to the signal line. You need a diode and transorb for each polarity. The transorb could be replaced by a string of diodes if the clamp voltage needs to be low. The deal is you need a low impedance clamp to protect the electronics. A series bulb just adds a little series resistance. This really only reduces current a bit.
 
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WBear2GCR
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« Reply #54 on: September 10, 2012, 11:16:06 PM »

Suggested schematic would be nice?

A concern with bias is that this requires a power supply to be working properly, and/or the unit to be on for protection. Quite frankly I leave my ant connected often with the receiver off... eventually I may pay for this...

                   _-_-bear

I was unable to locate any auctions by 4X4RB on ebay. Sad
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_-_- bear WB2GCR                   http://www.bearlabs.com
Steve - K4HX
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« Reply #55 on: September 11, 2012, 06:56:35 AM »

Quote
My original post was inquiring about protection when operating a receiver while I am transmitting on another HF band. So yes strong RF field.

The question was about protection in strong RF fields  - not ESD, lightning strikes, EMP, flight at 50k feet or any other such nonsense. Nitpickery is not productive. Whining about JS is not productive. Please take that crap elsewhere.
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WA1GFZ
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« Reply #56 on: September 11, 2012, 08:22:15 AM »

It is all the same voltage is voltage 1n34 are 60 year old nonsense
JS is JS
Science is science
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Rob K2CU
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« Reply #57 on: September 11, 2012, 11:24:55 AM »

For virtually all of the above mentioned protective circuits you will loose the desired signal when the protective circuit is shunting away the offending RF. Since you originally described transmitting on 75 while listening on a different band with a different antenna, then you have the classic multi-station contest interference issue. the best solution is to make up a coaxial trap for 75 and place it in the listening receiver's antenna input. An open circuit quarter wavelength (electrical) line T'ed to your input (stub) will get you something like 20+dB of attenuation for the undesired RF. An antenna tuner on the receiver will also help by rejecting some of the 75 meter RF. Many tuner configurations act like low pass filters and will do a good job at rejecting 75 when tuned to 160.

But, stay away from diode or other clipping type of circuit on the receiver as it will generate, and the receiving antenna radiate harmonics of the 75 M RF. It is just like the old rain gutter or wire fence with bad electrical (corroded) joints acting like diodes.
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N1XBM
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« Reply #58 on: September 11, 2012, 11:27:44 AM »

It is all the same voltage is voltage 1n34 are 60 year old nonsense
JS is JS
Science is science

WOW  If my 4-811a homebrew amp can generate as much strap as lighting bolts to a near by receiving antenna, then I must of botched something on the build. I never mentioned 1n34s in my original post.

I've already made my best attempts at lighting protection, but thank you for your input/concern. The original post is about strong RF fields at my home station.

I have a feeling your one of "those guys" who will keep replying for the last word. I'll do it my way and you can do it your way, if it doesn't work you can say " I told you so."

Will that make you happy?
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N1XBM
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« Reply #59 on: September 11, 2012, 11:30:56 AM »

For virtually all of the above mentioned protective circuits you will loose the desired signal when the protective circuit is shunting away the offending RF. Since you originally described transmitting on 75 while listening on a different band with a different antenna, then you have the classic multi-station contest interference issue. the best solution is to make up a coaxial trap for 75 and place it in the listening receiver's antenna input. An open circuit quarter wavelength (electrical) line T'ed to your input (stub) will get you something like 20+dB of attenuation for the undesired RF. An antenna tuner on the receiver will also help by rejecting some of the 75 meter RF. Many tuner configurations act like low pass filters and will do a good job at rejecting 75 when tuned to 160.

But, stay away from diode or other clipping type of circuit on the receiver as it will generate, and the receiving antenna radiate harmonics of the 75 M RF. It is just like the old rain gutter or wire fence with bad electrical (corroded) joints acting like diodes.

Good info here, something to think about and watch out for.
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KF1Z
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Are FETs supposed to glow like that?


« Reply #60 on: September 11, 2012, 11:58:30 AM »

I've always just used a relay to short the antenna input to the receiver during transmit.

Can still monitor my TX , and never lost a front-end yet.

Why over-complicate things?


Even is the RX is on another band... do you really need to monitor it
while you are transmitting?


If so, it seems like proper filtering on the transmitter, and reciever should eliminate any problems.

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KM1H
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« Reply #61 on: September 11, 2012, 06:52:04 PM »

Quote
Since you originally described transmitting on 75 while listening on a different band with a different antenna, then you have the classic multi-station contest interference issue.


Exactly as I tried to refer to it a while back on the thread and got crapped on and was not trying to stir up trouble. Since I often use 2 stations running in NON contest times I thought it was relevant to mention the primary use by many hams and was going to next get into the stubs next which I also use and are currently an active topic elsewhere. I can often be on one radio chasing DX on 160 CW and the other monitoring an AM QSO or looking for a DXpedition on another band/mode.

However they are not applicable in many antenna feeds without a lot of switching so a decision of the various methods suggested has to be made since the OP has several radios and antennas involved.

There are also several articles on bandpass and band reject passive filters for receivers or barefoot transmitters/transceivers. OTOH I doubt if anything will get into or out of the G-50 that would affect HF.

Carl
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Steve - K4HX
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« Reply #62 on: September 11, 2012, 09:02:42 PM »

OK show us some science. I'm sure the crew at PJ2T would love to be educated. Put up or shut up.


It is all the same voltage is voltage 1n34 are 60 year old nonsense
JS is JS
Science is science
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Steve - K4HX
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« Reply #63 on: September 11, 2012, 09:08:24 PM »

Best solution yet.  No PIN diodes or "science" required.  Wink


I've always just used a relay to short the antenna input to the receiver during transmit.

Can still monitor my TX , and never lost a front-end yet.

Why over-complicate things?


Even is the RX is on another band... do you really need to monitor it
while you are transmitting?


If so, it seems like proper filtering on the transmitter, and reciever should eliminate any problems.


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