Receiver Protection

[N1XBM]

Maybe I haven't search right, but as a practice I always disconnect all antennas to any other equipment I am not using if I am on the air. My thought is to protect the front ends of my radios.

My question is if I did want to leave a receiver up and running to monitor another band or a shortwave broadcast, is there something I can build to protect my receiver from high levels of RF.

[Pete, WA2CWA]

A lot depends on whether it's tube or solid-state receivers. Same band, different bands, how close the antennas, power levels, etc. Contest stations do it all the time.

[ke7trp]

So you want to have one radio and antenna receiving while you are transmitting on another radio on a different band?

Or are you talking about just a protection device for the front end for static, nearby lightning?

C

[W3RSW]

After the usual gap lightning protector or modern gas ionization model,  Phil, N8VB, recommends the following at the input of a receiver to prevent overload from nearby transmitters, etc. :

Ant input BNC (or whatever) to a 6.3v 150ma G-3/12 minature fuse style bulb (Mouser part #560-GF550)

Thence to a split of a 0.1uf/50 volt min. cap to receiver input terminal and
other side of split to a 1.0uf/50v. in series with back to back 1n4148 diodes (Mouser part 512-1n4148) to ground.  The diodes at time of pub. were in packs of 25 at $.02 each.

The bulb mounts in a Littlefuse holder, Mouser no. 576-03540101ZXGY

[ke7trp]

Thats a neat idea. 

I found another one that uses a simple Coax T.  You use SIX diodes.  Three one way and three the other way from Center of the unused T to the shield side of T.   Then you just plug it inline.

That device was intended to protect R390/A recievers from failed Coax relays and Static hits.

[N1XBM]

Ya I'm talking about a receiver on its own antenna listening to another band. A typical example for me is I am transmitting on 75m with 100 watts of carrier into my loop. I would like to be able to monitor 160 or a shortwave frequency on my R-392 or my softrock. Those receivers run on a separate dipole about 20 feet away from my loop.

Another example would be me transmitting on 75m with 100 watts of carrier and monitoring 6m with my G-50 with a halo about 30 feet away.

[WA3VJB]

The R-392 needs less protection than the Softrock.

At least three people on here will remember a time we were in a QSO on 75 meters, when suddenly a station on 1885 "appeared" in the QSO.  None of us let on that we heard the interloper, except one guy who was first to mention it.  

We almost had him convinced he had an image, or that the interloper had a spur.

Turns out, while one of us was transmitting, a receiver on the other band mistakenly was fed through the transmit chain on the other band. Conditions were so good, it sounded indeed like the other station had broken in and was just randomly talking to himself. Well not randomly, he was replying with a full page of notes.

The erroneous receiver was an R390A.

Poor guy who commented may have stared at his bottle, then the receiver, then the bottle again.

[The Slab Bacon]

The R-392 needs less protection than the Softrock.

At least three people on here will remember a time we were in a QSO on 75 meters, when suddenly a station on 1885 "appeared" in the QSO.  None of us let on that we heard the interloper, except one guy who was first to mention it.  

We almost had him convinced he had an image, or that the interloper had a spur.

Turns out, while one of us was transmitting, a receiver on the other band mistakenly was fed through the transmit chain on the other band. Conditions were so good, it sounded indeed like the other station had broken in and was just randomly talking to himself. Well not randomly, he was replying with a full page of notes.

The erroneous receiver was an R390A.

Poor guy who commented may have stared at his bottle, then the receiver, then the bottle again.

During the days of the Friday and Saturday evening break-in sessions, ya never qiute knew what was gonna happen or who would pop in.     

[Steve - K4HX]

Lots of people use this or similar on their receiving antennas (Beverages, etc) for receiver protection. You can build it yourself.

http://www.qsl.net/n/n1eu//topband/rxprot.htm

[WA1GFZ]

Steve that type of clipper can produce lots of IMD. I suggest the diodes be changed to pin diodes. Trr should be nice and slow maybe greater than 500ns for 160m

[Steve - K4HX]

IMD when receiving?

[WA1GFZ]

any strong local signal that can drive the diodes into conduction can produce IMD

[WBear2GCR]

Speaking of PIN diodes, where are sources for them??

                     _-_-bear

[Pete, WA2CWA]

Speaking of PIN diodes, where are sources for them??

                     _-_-bear

The first 3 hits on Google: Buying PIN diodes

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[Steve - K4HX]

It would have to be so strong as to cause damage to the receiver. I can't think of any real world situation like this unless you live next to a BC station.

any strong local signal that can drive the diodes into conduction can produce IMD

[kb3ouk]

Or you have an antenna changeover sequencing problem and accidentally feed something like a kw carrier right in to the receiver.

[Steve - K4HX]

All bets are off then.  

Here's another one where the diode can be switched in or out.

http://pvrc.org/~n4zr/Articles/Simple%20Protection%20for%20the%20Fledgling%20SO2R%20Station.pdf

[WA1GFZ]

The Racal RA6830 can handle 20 watts input. The limiter is 2 banks of 1N4148 diodes biased with voltage regulators. It is a high level clipper. and generates some distortion but saves the front end.

[ke7trp]

The FT101 has survived since the 70s with a simple bulb like the one that was mentioned.  I use one on low power 160 meter AM (my friend is 10 miles away).  I found the bulb popped a few times now.  I left the 101 on the inverted L and fired up the 304TL rig on the inverted V. 

So maybe that is all he needs?  Lots of good ideas so far!

C

[kb3ouk]

The FT-901 uses a really low milliamp fuse, and that thing won't blow, it glows. I've fired up a rig into one antenna while the 901 is hooked to another, and it lights up like a nightlight.

[Bill, KD0HG]

The FT-901 uses a really low milliamp fuse, and that thing won't blow, it glows. I've fired up a rig into one antenna while the 901 is hooked to another, and it lights up like a nightlight.

When I worked on military radios, the R-1051 receiver (to this day) used a 6BZ6 and 6AN5 in the front end. The rest of the receiver all transistor. Simply because hollow state is inherently robust. A spark or overload won't kill a 6BZ6, and it's simple enough to pop a new one in if you need to.

Bill

[ke7trp]

Good point Bill. I worry about coils.  We have an SX28A that was dead.  We found an RF coil blown open. That super small wire was a PAIN to fix.  Not sure if a diode device would have saved her or not.

C

[W3RSW]

Everything is a risk and a set of compromises if the standard of protection is set too high.
A direct lightning hit will fry diodes, hard switches, jump the gap of fuses and probably blow everything in the shack, maybe even the house, .... so pick your poison.

Try real hard not to get too fancy with multiple switched rigs on the same or multiple antennae too. Maybe a start menu similar to an aircraft pilot's would help. 

...sooner or later. 

SWL 's have  1/4 the problem (inverse square). 

[WD5JKO]

Everything is a risk and a set of compromises if the standard of protection is set too high.
A direct lightning hit will fry diodes, hard switches, jump the gap of fuses and probably blow everything in the shack, maybe even the house, .... so pick your poison.

  I took a direct hit here a few years back. My neighbor saw the lightning bolt dancing to the tip of my antenna mast. I insulate the mast, and it is part of an antenna. I usually have a knife switch thrown outside, but this time not. I did have a coax switch in the shack thrown which grounded the antenna, and diverted my shack ham stuff to a 50 ohm dummy load. The next coax switch had my Icom R75 in line.

  The result? None of my ham equipment was damaged! But all around the house there was dead bisquets including: AC Programmable thermostat, AC ventilator control PCB, 1 garage door opener, and every HDMI port in the house. The HDMI ports were in multiple TV/GAME/Computer boxes. If a cable was plugged into the port, the port was fried.

   So one thing we can do, as a single layer of protection, would be to have a relay box in the shack that grounds the incoming antenna feed, and terminates the shack side into a dummy load whenever the shack power strip is powered OFF. So when that unexpected storm pops up suddenly, and your away and you forgot to disconnect things, at least there is 1 layer of protection in place.

Jim
WD5JKO

[ke7trp]

My shack is setup to ground everything when I turn the light off and leave the room.  The light switch controls a lamp socket pair.  Hooked to that is the power supply for my grounding antenna switch.  The feeders go to ground and the radios go to dummy loads all when I walk out of the room and turn off the light.   If I forget to turn out the light, then all bets are off..

C