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Diodes to protect antenna/receiver??

R

Ron G

Jan 1, 1970
0
Hi--

I have read the posts on using NE 51 H's for protecting short wave receivers
from static/lightening on a long wire antenna line.

Since these "fire" at about 70 V, it really seems high.

Would a pair of 1N4004's, back to back in parallel, protect better?

They would go into full conduction at about 0.6 volt, and wired parallel,
reversed, seem to be a better choice.

Is it a matter of RF response time?

Thanks---
Ron
 
H

Herbert Blenner

Jan 1, 1970
0
Subject: Diodes to protect antenna/receiver??
From: "Ron G" [email protected]
Date: 10/22/03 11:22 PM Eastern Daylight Time
Message-id: <[email protected]>

Hi--

I have read the posts on using NE 51 H's for protecting short wave receivers
from static/lightening on a long wire antenna line.

Since these "fire" at about 70 V, it really seems high.

Would a pair of 1N4004's, back to back in parallel, protect better?

Blocking diodes have capacitance and would shunt RF signals.

Herbert
 
R

René

Jan 1, 1970
0
Blocking diodes have capacitance and would shunt RF signals.

Herbert
If it has to be diodes, check the 1N4148, preferrably in the minimelf
incarnation, they have fairly small capacitance.

My outgoing mail is in plain text! :)
 
T

Tim Shoppa

Jan 1, 1970
0
Blocking diodes have capacitance and would shunt RF signals.

Whether this is relevant or not depends on the impedance of the
RF signals. At 15MHz, 10 pF has an impedance of around 1k ohm. That's
negligible if you have a 50-ohm antenna; for a random longwire with a
much higher impedance it may be relevant.

A much more likely problem is intermod caused by nearby large-signal MW AM
broadcasters mixing via the protection diodes.

Sidactors are low-capacitance devices with trip voltages above
forward-biased diodes but less than gas discharge tubes.

The PRIMARY goal of "lightning-arrestor" type devices is to stop the
radio from bursting in flames in case of a nearby lightning hit. From a
safety perspective whether the radio works or not afterwards
doesn't matter much.

Having a good low-impedance ground (bonded to the AC service entrance's ground,
that's vitally important although I didn't know why until recently!) for the
protector is vital. It'll also help radio reception :)

Tim.
 
K

Ken Taylor

Jan 1, 1970
0
Tim Shoppa said:
[email protected] (Herbert Blenner) wrote in message

Whether this is relevant or not depends on the impedance of the
RF signals. At 15MHz, 10 pF has an impedance of around 1k ohm. That's
negligible if you have a 50-ohm antenna; for a random longwire with a
much higher impedance it may be relevant.

A much more likely problem is intermod caused by nearby large-signal MW AM
broadcasters mixing via the protection diodes.

Sidactors are low-capacitance devices with trip voltages above
forward-biased diodes but less than gas discharge tubes.

The PRIMARY goal of "lightning-arrestor" type devices is to stop the
radio from bursting in flames in case of a nearby lightning hit. From a
safety perspective whether the radio works or not afterwards
doesn't matter much.

Which is why these diodes won't do the trick - they'll burst into flames and
not be present to protect the radio, long before the surge current has
dissipated.

Ken
 
M

Michael

Jan 1, 1970
0
Which is why these diodes won't do the trick - they'll burst into flames and
not be present to protect the radio, long before the surge current has
dissipated.

Ken

Great Scott!!!, 1.21 GIGA WATTS!
 
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