[HomeBrew] Validity of protection from available coaxial surge Protectors?

[Bill Cromwell]

On 04/04/2014 08:38 PM, Ray, W4BYG wrote:
> ** Please do NOT cross-post messages when posting to HOMEBREW **
>
> I would like to open up a conversation on how much receiver front end
> protection is actually afforded with the currently available coaxial surge
> protectors.
>   
> My question to the list:  Is there anyone who is knowledgeable or
> experienced on what kind of thru levels are typically sustainable by today's
> modern receivers/transceivers?  Has there been any research on the subject?
> Or is it all conjecture?
>   
> My quest started out with trying to find out at what level and over what
> period of time commonly available coaxial surge protectors kicked in.
> Numerous brands are available from $25 or so, up to about $90.  With
> multiple antennas and expensive rigs of today, it seems important to be able
> to characterize the level of protection one is buying.
>   
> Technical information is not very well published by the various brands.  I
> haven't seen much published on what is needed.  The protector marketing
> types just say buy ours and you will be protected.  That seems like a bit of
> "snake oil" to me, kind of like days of old, out West.
>   
> Without wanting to reflect poorly on MFJ, I had occasion to query a past
> employee of theirs on the technical details of their coaxial surge
> protectors.  The gentleman genuinely tried to find out the information, but
> was unable to provide any engineering wisdom as to what represents real
> protection.
>   
> Regarding their product he shared they had not done any actual testing of
> the gas surge protectors.  They just trusted the Asian manufacturer's specs.
> Also there was no real information about what does it take to actually
> protect the front end of a receiver or transceiver, from induced surges on
> an antenna.  I understand virtually nothing can protect you from a direct
> lightning hit, but nearby strikes can induce a lot of possibly divertible
> energy.  In response to my query on one MFJ model I got:
>   
> The gas discharge tube in MFJ-272 is SRYG-1000L.
>   
> 1. DC breakdown voltage(100V/s):  800~1200V
> 2. Impulse breakdown voltage(100V/μ s):  1500V
> 3. Max. Withstanding current(8/20μs):  5kA
> 4. Impulse discharge withstanding life( 8/20μs, 100A):  300
> 5. The minimum Insulation resistance at DC100V(GΩ ):  10
> 6. Max. Capacitance(pF):  1.5
>   
> I then replied in part:
>   
> ...The numbers confirm my concern about just how much protection can there
> be letting a several μs pulse up to 1500 volts (in 15μs?) into the front end
> of a transceiver or receiver before the devices fires and shorts out the
> energy to ground.  I don't have any factual insight on this.
>   
> I would appreciate any comments from those that have tested this subject and
> have come to some reasonable resolve.
>   
> I understand the need for a trigger voltage somewhat above what might be
> experienced with a kilowatt transmitter and a moderately high SWR on the TX
> line.  1000 watts of RF at 50 ohms could produce about 223 volts RF.  At 100
> ohms load (2:1 SWR?), there could be about 316 volts of RF, etc.   For
> peak-to-peak voltages, I would multiply both numbers by 2.828 for 630.6 v
> P-P and 893.6 v P-P respectively.
>   
> With such a device as spec'd ... I just wonder if there is any real
> protection of the receiver first active stages other than possible
> protection from fire in the shack?...
>   
> I repeat my question:
> Is there anyone who is knowledgeable or experienced on what kind of thru
> levels are typically sustainable by today's modern receivers/transceivers?
> Has there been any research on the subject?  Where can one find it?  Or, is
> it mostly conjecture?
>   
> Your attention and thoughtfulness is appreciated.
> Ray, W4BYG
>   
>
Hi Ray,

I looked into this some time ago. You aren't going to get a lot of 
protection from "a gas discharge" tube. You really can protect delicate 
equipment form direct light lightning hits. But that requires a system 
approach. $pell that with lot$ of dollar$. I don't know why you need to 
operate when thunderstorms are approaching but I'm just an amateur and I 
don't need to. I elected the much cheaper route of unplugging and 
disconnecting *everything*. I'll see if I can find the name of that 
company and point you at their web site. I think it's something like 
Poly-Phaser. They have the numbers and the info you want. They'll sell 
you as much or as little protection as you want. And yes - they have 
documented cell and trunking sites taking multiple direct hits and 
surviving.