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Author Topic: Coax antenna isolation  (Read 330 times)

IK2HKT

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Coax antenna isolation
« on: February 17, 2021, 08:33:18 AM »

Hello! - I am Stefano IK2HKT from Italy.
I wrote the same post in the "Antennas, Towers and more" section but I think it is also of interest in this section of the forum.

I would like to introduce you the result of a long work during these months of Covid 19 pandemic.
I called him "Antenna Breaker".
You can watch a short video at the following youtube address:

< https://www.youtube.com/watch?v=tSpX53cnlwg >

This device was designed by radio amateurs for radio amateurs based on 20 years of experience designing and operating HAM Radio remote stations.
The main RF features are here thereafter described:
1)   It protects the Radio equipment versus static buildup and to some extent (see note § X.X) versus lighting
      discharges. Up to 6 coaxial cables can be completely disconnected each other both at shield that at pin level.
2)   No common ground connection is employed to avoid static cross-talk.
3)   It avoids the need to manipulate and therefore to disconnect coaxial cables during a critical condition such as a
      thunderstorm or when the access to the coaxial cable is not immediate.
4)   N connectors are used to allow high power handling (up to 5 KW RMS) capability  together with a low insertion
      loss and a negligible mismatch (better than RL <-35dB @ 30 MHz).
5)   Rugged polymethyl metacrylate structure with a high isolation capability up to 40Kv/mm.

Are important key aspects are:
a)   To allow the accuracy required, the structure is realized with a laser cutter machine.
b)   Easy operation between 12 up to 14 Volts.
c)   The mechanical action is performed by a 12V piston linear actuator with internal limit switch. It can be operated in
      manual, semi-auto or auto mode. The auto-mode case is  triggered by the radio  on/off switch.
d)   The whole system is protected by 2 re-settable fuses, one for the 12V line and the other on the auxiliary voltage
      for the auto mode.
e)   The device so far designed, it shall be considered for indoor use
 
see note § X.X
During a direct or even indirect lightning strikes, because of their nature, complete isolation cannot be guaranteed. By the way,  based on our experience it represents a valid solution against lighting mainly indirect and trough ground.
In addition to the use of the Antenna Breaker, it is advisable to insert a contactor on the radio station electrical power system, in order to further protect and isolate your equipment.

This is not a commercial item but if anyone is interested in having it, please, contact me by email.

73 - Stefano
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KH6AQ

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Re: Coax antenna isolation
« Reply #1 on: March 01, 2021, 04:32:07 PM »

Very nice!

I do wonder about the choice of material though. FR-4 is flame resistant and is rated 94V-0. PMMA is not flame resistant, is it?
« Last Edit: March 01, 2021, 04:52:43 PM by KH6AQ »
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IK2HKT

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  • Posts: 6
Re: Coax antenna isolation
« Reply #2 on: March 03, 2021, 09:45:43 AM »

Hi David,
as far as the material is concerned, the FR-4 is certainly more flame resistant but the FR-4 is too flexible compared to PMMA. This device needs a rugged structure for the precision of insertion of the connectors.
 
Also, having regard to my esperience, I  think the flame resistant is not a problem; I have built several Antenna Breaker during last year and,  despite the lightning that fell this summer in Europe, none had problems with overheating and not even with flame.

A further problem is that which I don't think is easy to find FR-4 material in right thickness (unless you do industrial quantities and also regarding the price!). The Antenna Breaker is made with PMMA 4" thick and about 8" thick for the two reinforced connectors panels.

Anyway, I have updated the video with English comment here: https://www.youtube.com/watch?v=iJ0ZAiVUb4E).

I am at your disposal for any other questions and/or suggestions.

73 - Stefano
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IK2HKT

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  • Posts: 6
Re: Coax antenna isolation
« Reply #3 on: March 03, 2021, 10:00:37 AM »

My mistake !

The thick is 0,4" and 0,8 "

 
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