RF Clipper Diode Design


Bill Alpert
 

I’m looking for an inline device that will protect my SDRs from adjacent transmitter antennas. DXE sells such a device but it’s almost $100. Any tips appreciated. I’m not much of a builder.
--
73 de Bill / KG6NRV


Simon Brown
 

$100 is a bit much 😊

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Bill Alpert
Sent: 30 January 2020 16:08
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] RF Clipper Diode Design

 

I’m looking for an inline device that will protect my SDRs from adjacent transmitter antennas. DXE sells such a device but it’s almost $100. Any tips appreciated. I’m not much of a builder.
--
73 de Bill / KG6NRV


Kriss Kliegle KA1GJU
 

   When you say "local transmitters" am I safe to assume you mean yours?
  
   I use a simple DPDT relay that disconnects the antenna from the SDR, and grounds the SDR input.
The relay is energized via the 13.8Vdc available on pins 3 & 4 of the local Icom's Auto Tuner port.
I have two Icoms, one in shack and one remote in the repeater shed. With diodes to protect back
feeding the Icom not in use, if either radio is turned on, my SDR server antenna(s) get disconnected.
Parts all from junk box, aka FREE. Old UPS's have relays and plenty of diodes for the taking. Don't forget the
diode across the relay coil, and mind the polarity! 

  Works with Kenwood rigs too on their auto tuner port, which only goes 'hot' when rig is powered up.

   One could have it only energize during TX, via one of the rear connections that goes high or low (watch the maximum rated current and voltage!), but I don't want to take a chance of RF sneaking in while the relay is in transit! Plus it would be more complicated due to the low maximum allowed current through the internal port. I have two relays one in shack and one in shed 120' away, both feeding numerous SDR's and servers. Once I move the servers to the far opposite end of property, then the RF overload will not damage them during local TX. Have to run some figures for operating the 1200 watt linear though, but at 100 watts, no issues.

   If you are not good with a soldering iron, I suggest you look for the following devices on a table at your local ham flea market:


They are easy to pick out on a sellers table due to their ugly shape, but typically here in NH I pay ~$25 for them. They can have BNC, N, or UHF connectors on them. Obviously the less adapters inline, the less for things to go wrong and fail. New they are ~$100 +/- !

Here's the link to see more:
https://www.google.com/search?rlz=1C1DVJR_enUS838US839&tbm=isch&sxsrf=ACYBGNQdRoSwucTl3_4p14Q-JNIuB7JfGA%3A1580406878990&sa=1&ei=XhgzXpj9O8aOggf8rpWYAw&q=Coaxial+relay&oq=Coaxial+relay&gs_l=img.3..0i67l2j0i5i30j0i24.75346.78164..78415...1.0..0.97.1173.14......0....1..gws-wiz-img.....10..35i39j35i362i39j0j0i131j0i3j0i8i30.Gs1-y-sxrVs&ved=0ahUKEwiYpP208qvnAhVGh-AKHXxXBTMQ4dUDCAc&uact=5#imgdii=dQfC6LOO7r_r3M:&imgrc=rpAIpk0MZiuMEM:


73 Kriss KA1GJU



Tracey Gardner
 

 
How about a Mini-Circuits RF Limiter?
This one is half the price of the DXE one.
 
 
73s Tracey G5VU
 
 
 

----- Original Message -----
From: Simon Brown <simon@...>
Reply-To: <main@SDR-Radio.groups.io>
To: <main@SDR-Radio.groups.io>
Sent: 30/01/2020 16:10:36
Subject: Re: [SDR-Radio] RF Clipper Diode Design

$100 is a bit much 😊

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Bill Alpert
Sent: 30 January 2020 16:08
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] RF Clipper Diode Design

 

I’m looking for an inline device that will protect my SDRs from adjacent transmitter antennas. DXE sells such a device but it’s almost $100. Any tips appreciated. I’m not much of a builder.
--
73 de Bill / KG6NRV


john@...
 

Array Solutions sells one for $69.

https://www.arraysolutions.com/as-rxfep

 

73, John W1JA

 

From: main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of Tracey Gardner via Groups.Io
Sent: Thursday, January 30, 2020 1:10 PM
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] RF Clipper Diode Design

 

 

How about a Mini-Circuits RF Limiter?

This one is half the price of the DXE one.

 

 

73s Tracey G5VU

 

 

 

----- Original Message -----

From: Simon Brown <simon@...>

Reply-To: <main@SDR-Radio.groups.io>

To: <main@SDR-Radio.groups.io>

Sent: 30/01/2020 16:10:36

Subject: Re: [SDR-Radio] RF Clipper Diode Design


$100 is a bit much 😊

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Bill Alpert
Sent: 30 January 2020 16:08
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] RF Clipper Diode Design

 

I’m looking for an inline device that will protect my SDRs from adjacent transmitter antennas. DXE sells such a device but it’s almost $100. Any tips appreciated. I’m not much of a builder.
--
73 de Bill / KG6NRV


Roger Need
 

There are basically three ways to protect your SDR receivers

- A manual switch which switches your antenna from the transceiver to the SDR (you need about 50-60 dB of isolation for 100 W Tx)
- An automatic switch which shorts the Rx input to ground when transmitting. There are several vendors (Elad, Heros, DXE, MFJ) in different price ranges but they all switch based on the Send line on the transceiver or by RF sensing
- An inline RF limiter protection box on the SDR antenna input.  You can easily build your own in a metal box with a couple of connectors and some basic circuitry.  Or you can buy them from a number of companies (Array Solutions, DXE, Cross Country Wireless, DEO, Chinese on eBay)

Each method has advantages and disadvantages.  One thing to note about  the inline RF limiters.  Just about all of them use diodes to limit the input power and this can cause some minor degradation in high-end receiver performance due to unwanted mixing in the diodes (even well below safe power levels) .

Roger


d9aplus
 

For reference,
RF signal sharing and protection of two receivers. 
Diodes are 1N4148.
In use since 2015. recently sustained one near strike, Sony ICF 2001D was on one port and
SDRPlay RSP1 on another... no damage.



Stephen Matthias
 

what frequencies are you broadcasting on and what power will you use?


On Thu, Jan 30, 2020 at 11:08 AM Bill Alpert <billalpert@...> wrote:
I’m looking for an inline device that will protect my SDRs from adjacent transmitter antennas. DXE sells such a device but it’s almost $100. Any tips appreciated. I’m not much of a builder.
--
73 de Bill / KG6NRV


Bill Alpert
 

100 watts max, 80 - 10 meters, most of my activity is on 40. Thanks
--
73 de Bill / KG6NRV


Martin
 

For simplicity, when used in a 50 Ohm circuit, a pair of back to back 1N4148 diodes across the signal path is hard to beat.

They limit the maximum RF level at around +10dBm, which is typically a safe level for most receivers, but is still high enough a value to avoid significant contribution to intermodulation distortion when used in most amateur receive systems.

If you wish make it even safer add a low wattage (typically 100mW) light bulb on the antenna side (not the radio side as the diodes will conduct before the bulb lights) of the diodes. If enough current is flowing to make the bulb light up, its DC resistance will increase and provide even further protection, and if the RF level is excessive the bulb will blow and act as a fuse before the diodes burn out.

Regards,

Martin - G8JNJ

 






jdow
 

1N4148 diodes are fairly slow and have a small sustained power rating. At HF they may work OK, though, if you do not feed sustained high power through them.

{o.o}

On 20200201 09:35:55, Martin via Groups.Io wrote:
For simplicity, when used in a 50 Ohm circuit, a pair of back to back 1N4148 diodes across the signal path is hard to beat.
They limit the maximum RF level at around +10dBm, which is typically a safe level for most receivers, but is still high enough a value to avoid significant contribution to intermodulation distortion when used in most amateur receive systems.
If you wish make it even safer add a low wattage (typically 100mW) light bulb on the antenna side (not the radio side as the diodes will conduct before the bulb lights) of the diodes. If enough current is flowing to make the bulb light up, its DC resistance will increase and provide even further protection, and if the RF level is excessive the bulb will blow and act as a fuse before the diodes burn out.
Regards,
Martin - G8JNJ


goscickiw
 

What if I want to protect my device from everything stronger than 0dBm, or maybe even -5dBm? I don't think 1N4148's forward voltage is that low. What would you suggest? Schottky? Germanium?


MVS Sarma
 

4148 will withstand 75v on reverse. Schottkey or germanium  i dint think they can. However  4148 two pieces in reverse parallel  should do your job.

All th best
Sarma  vu3zmv

On Sun, 2 Feb 2020, 2:20 pm goscickiw, <goscickiw@...> wrote:
What if I want to protect my device from everything stronger than 0dBm, or maybe even -5dBm? I don't think 1N4148's forward voltage is that low. What would you suggest? Schottky? Germanium?




jdow
 

A PTT relay switching high attenuation?
Really - the lower your protection power that leaks through the worse your IMD performance will become. It's a nasty tradeoff - but - it's the physics of reality.
{^_^}

On 20200202 00:50:50, goscickiw wrote:
What if I want to protect my device from everything stronger than 0dBm, or maybe even -5dBm? I don't think 1N4148's forward voltage is that low. What would you suggest? Schottky? Germanium?


jdow
 

Their problem is power dissipation. If it is protecting you from 10 watts coming in on the feedline then that has to go somewhere, like into the diodes. Pretty soon little puffs of magic blue smoke will appear and the magical electronics will not longer work their magic.

{^_^}

On 20200202 01:18:57, MVS Sarma wrote:
4148 will withstand 75v on reverse. Schottkey or germanium  i dint think they can. However  4148 two pieces in reverse parallel  should do your job.
All th best
Sarma  vu3zmv
On Sun, 2 Feb 2020, 2:20 pm goscickiw, <goscickiw@... <mailto:goscickiw@...>> wrote:
What if I want to protect my device from everything stronger than 0dBm, or
maybe even -5dBm? I don't think 1N4148's forward voltage is that low. What
would you suggest? Schottky? Germanium?


goscickiw
 

I don't think there will ever be a situation where I put 75V on the input of my SDR - unless I do something ultra stupid. I won't put transmitters on the same line. I just want to protect my HackRF (notorious for getting damaged by strong signals) from a big broadcast transmitter 3km away.


MVS Sarma
 

Yoy need a trap for the bc transmitter fewuency. May be two such traps in series . The traps and later sections should all be in shielded enlosure. 
Even the rx devicecshould be in shielded snd grounded with shortest path.

On Sun, 2 Feb 2020, 3:18 pm goscickiw, <goscickiw@...> wrote:
I don't think there will ever be a situation where I put 75V on the input of my SDR - unless I do something ultra stupid. I won't put transmitters on the same line. I just want to protect my HackRF (notorious for getting damaged by strong signals) from a big broadcast transmitter 3km away.


jdow
 

If you put the diodes in parallel back to back the 75v reverse voltage limit is academic. It will never go above 1V until the other diode gives up its magic blue smoke.

{^_^}

On 20200202 01:48:23, goscickiw wrote:
I don't think there will ever be a situation where I put 75V on the input of my SDR - unless I do something ultra stupid. I won't put transmitters on the same line. I just want to protect my HackRF (notorious for getting damaged by strong signals) from a big broadcast transmitter <https://en.wikipedia.org/wiki/FM-_and_TV-mast_Olsztyn-Pieczewo> 3km away.


jdow
 

Hm, that's a big one. You can expect "volts" on your antenna. The best solution is, indeed, traps. A set of series LC filters shunting the transmission line is probably the best solution. You'd want one for every frequency. For the wide band (>1MHz)signals you probably want filters that reject the whole band of frequencies. Off hand I don't know a good source for anything other than FM band rejection.

The back to back diodes would protect nicely. But they would probably generate spurious signals all over the spectrum. (Nonetheless, it's worth a try. Your particular horse might learn to sing.)

{^_^}

On 20200202 01:58:13, MVS Sarma wrote:
Yoy need a trap for the bc transmitter fewuency. May be two such traps in series . The traps and later sections should all be in shielded enlosure.
Even the rx devicecshould be in shielded snd grounded with shortest path.
On Sun, 2 Feb 2020, 3:18 pm goscickiw, <goscickiw@... <mailto:goscickiw@...>> wrote:
I don't think there will ever be a situation where I put 75V on the input of
my SDR - unless I do something ultra stupid. I won't put transmitters on the
same line. I just want to protect my HackRF (notorious for getting damaged
by strong signals) from a big broadcast transmitter
<https://en.wikipedia.org/wiki/FM-_and_TV-mast_Olsztyn-Pieczewo> 3km away.


MVS Sarma
 

I  understood thatvyoucarectrying to clip the signal. Local broad cast signal cant be killed like that. You have to have band stop  filteŕs in tandem 


On Sun, 2 Feb 2020, 3:44 pm jdow, <jdow@...> wrote:
Hm, that's a big one. You can expect "volts" on your antenna. The best solution
is, indeed, traps. A set of series LC filters shunting the transmission line is
probably the best solution. You'd want one for every frequency. For the wide
band (>1MHz)signals you probably want filters that reject the whole band of
frequencies. Off hand I don't know a good source for anything other than FM band
rejection.

The back to back diodes would protect nicely. But they would probably generate
spurious signals all over the spectrum. (Nonetheless, it's worth a try. Your
particular horse might learn to sing.)

{^_^}

On 20200202 01:58:13, MVS Sarma wrote:
> Yoy need a trap for the bc transmitter fewuency. May be two such traps in series
> . The traps and later sections should all be in shielded enlosure.
> Even the rx devicecshould be in shielded snd grounded with shortest path.
>
> On Sun, 2 Feb 2020, 3:18 pm goscickiw, <goscickiw@...
> <mailto:goscickiw@...>> wrote:
>
>     I don't think there will ever be a situation where I put 75V on the input of
>     my SDR - unless I do something ultra stupid. I won't put transmitters on the
>     same line. I just want to protect my HackRF (notorious for getting damaged
>     by strong signals) from a big broadcast transmitter
>     <https://en.wikipedia.org/wiki/FM-_and_TV-mast_Olsztyn-Pieczewo> 3km away.
>
>