Burnt DV-Micro is NOT toast!

       RF Gaskets do double duty

As is well known in the industry, Davicom’s remote site management products are robust and designed to handle the harsh RF environments often found at remote transmitter sites. One design feature used to attain this “RF robustness” is our integration of flexible RF gaskets into the chassis design of certain products.

Davicom RF gasket

Photo 1. Sample of RF gasket used in Davicom’s DV-Micro.

Davicom intelligent site management systems RF gasket

Photo 2. Close-up view of RF gasket.

 

The use of these gaskets and other design features allows the DV-Micro to operate reliably in electrical fields of up to 10V/m at frequencies between 30MHz and 1GHz. The flexible metal gasket prevents any RF leakage from being emitted outside the chassis, but more importantly, it also prevents any high RF fields from entering the box and affecting operation of the electronics inside.

 

Who would have thought that these little gaskets would also serve a purpose during a site fire?

On June 4th 2017, a fire destroyed KHCB’s Madisonville, Texas FM transmitter site.  Lightning is the suspected catalyst for the fire.

Transmitters at site after fire

Photo 3. View of transmitters

rack after fire

Photo 4. View of equipment rack

Paul Easter, KHCB’s Technical Director and his engineering team quickly put the site back on the air with a temporary shelter and backup equipment. While cleaning-up the site, Paul noticed his remote-control unit (a Davicom DV-Micro) blackened, but still mounted in its rack. He took it out and brought it back to his Houston headquarters. Even if, on the outside, it didn’t look pretty, Paul decided to try powering-up the unit to see if it was operational. When it did power-up, he decided to try connecting to it and downloading the site’s event log, which he did obtain.

As it happened, I was visiting Houston to do a presentation at the July SBE lunch meeting, so Paul gave me the unit and I brought it back to the Davicom factory for complete tests and a repair estimation.

 

front view DV-Micro after fire

Photo 5. Front panel view of DV-Micro that was in fire

DV-Micro back after fire

Photo 6. Rear panel view of DV-Micro that was in fire

 

Once back at the office, I gave the unit to the production department and asked them to take the unit as it was, and to run the full post-production tests on it, as if it was being shipped out to a customer. Apart from the blackened chassis and semi-melted front faceplate, it passed on every count!

See a video of this unit being powered-up here:


DV-Micro after fire internal view

Photo 7. Internal view. All circuits and parts inside the chassis were clean and operational.

Our theory is that the RF gasket prevented any fire or hot gasses from entering the chassis and destroying the electronics inside. The following pictures show the detail of these gaskets.

 

DV-Micro RF gasket cover

Photo 8. View of one of the 4 RF gaskets used on the chassis of the DV-Micro

 

DV-Micro cover

Photo 9. Close-up view of RF gasket showing burned outside and clean inside

 

All this goes to show that good design costs more, but always adds value, sometimes in unexpected ways!

 

DV-Micro front view with fire

John Ahern

July 2017

Special thanks go to Paul Easter and to the good folks at KHCB for allowing us to use their pictures and to tell the story of this unfortunate event at their Madisonville site.

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