[TowerTalk] from towers to shack
glhuber at msn.com
Tue Dec 10 00:00:59 EST 2013
Here's another MOV solution;
http://www.arraysolutions.com/images/SurgeSupressorManual_1.pdf ..... simply
(8 or 16) 65 volt MOVs in a NEMA box. I mounted the 16 terminal version at
the ground window and cable entrance of my shack. The ground window is
bonded to the tower ground system on the outside and is also bonded to the
supplemental and primary system electrical ground systems in accordance with
the National Electrical Code. For coaxial cables, I use bulkhead connectors
to penetrate the ground window (aluminum plate , Plexiglas / plastic ,
aluminum plate sandwich) with ICE co-axial protectors;
73 ES DX,
Gary -- AB9M
From: Roger (K8RI) on TT
Sent: Monday, December 09, 2013 10:08 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] from towers to shack
On 12/9/2013 10:35 PM, john at kk9a.com wrote:
> I wonder why transorbs and gas discharge tubes are not commonly used to
> protect control lines in ham radio installations? The $135 Polyphaser
> IS-RCT just has eight inexpensive MOVs inside. I used GDTs on one rotator
> where I got tired of replacing leaky MOVs and it has worked fine for over
> year and though one direct lightning strike.
Gas discharge tubes have too high a breakover voltage to protect most
solid state devices.
They are fine for most rotator controls.
> John KK9A
> To:towertalk at contesting.com
> Subject:Re: [TowerTalk] from towers to shack
> From:Jim Lux <jimlux at earthlink.net>
> Date:Mon, 09 Dec 2013 06:58:08 -0800
> List-post:<towertalk at contesting.com">mailto:towertalk at contesting.com>
> On 12/9/13 6:23 AM, john at kk9a.com wrote:
> Polyphaser rotator protectors are very expensive. I would not wait too
> long to protect your system. You can purchase MOVs for very little cost.
> I would suggest using TranZorb type devices (basically back to back
> as clamps rather than MOVs, or even better, some sort of 4 layer device
> a Diac.
> Mouser has them in a variety of voltages and ratings.. about $1-2 each
> MOVs die a little each time they take a hit, with the leakage current
> increasing. Their only big advantage is that in large quantities they are
> very cheap and a loose tolerance part to manufacture, so consumer plug
> strips which need to sell for a few bucks can afford them. They're cheap
> make physically large, too, which helps with the energy dissipation.
> A clamp works the same every time. The disadvantage of a Zener type clamp
> that the voltage drop is constant, so if there's significant current, the
> power dissipation can be high. For a short duration transient this may not
> be an issue, or one can put series impedance in the system to limit the
> transient current. An LC low pass filter probably wouldn't be a bad idea
> a rotor control line, since it's not like you're trying to pass RF.
> 4 layer negative resistance devices (Diacs), or even neon bulbs (NE2) or
> even better, Vacuum Spark gaps, are nice because once they breakdown, the
> voltage drops dramatically, reducing the power dissipation.
> Here's a typical gas tube type TVS
> Mouser has tons of these from various mfrs, and they run about a 50 cents
> buck each. Look for "Gas Discharge Tubes" The lowest voltage is typically
> around 70V, so they're good for protecting 24VAC circuits (about twice the
> peak V), but not so good for circuits that directly touch ICs, where you
> need the 5-10V zener type clamps.
> The challenge with a spark gap (in air) is that the minimum breakdown
> voltage is around 300V. That's fine for a coax line running power, but not
> so great for a 12 or 24VDC line. So what I would do is combine the spark
> (which will clamp to 300-400 V) with some other device to take it the rest
> of the way (with some current limiting component between spark gap and
> device) (Gas Discharge Tubes use some gas like Argon at low pressure with
> lower minimum sparking voltage)
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