[RFI] RFI suppression cores for 147 MHz

[Dale]

Cortland,

Thank you for the kind words AND for pointing out that the Switch or Router is a Class A device.  I missed that part.  Yes, it was good to see you in the lab when you visited a few years ago.  

Jeff, I have to ask: Do you really need all of those ports on the Netgear box?  If not, I'd opt for one with fewer ports and a Class B rating.  Do not forget to cover all unused ports with conductive material that is in contact with the chassis.

Options for correcting the 2m interference issue are getting a bit thin.  If the measures described are not sufficient. try applying the ferrite materials.  If those fail, then you really are down to choosing one of two paths:

1.  Get the entire LAN wiring system farther away from the 2m system and/or its antennas, as separation distance between source and victim helps to the tune of the inverse square principle.

2.  Prepare to spend a lot of time and money on modifying the LAN hardware to greatly lower its emissions.  This has been done when necessray to get commercial equipment to meet aerospace specs.  The net result is larger and more bulky than the original equipment, it usually needs to be repackaged. and the starting point is a total changing of interconnect cabling to either hard wiring or the use of proper metal connectors with back shells.  Cost on those will be aomewhere around $10 to $15 per connector times the number of cables times 2 (one such connector at each end of each cable).  It is not a pretty sight.

Cortland talks about connectors using Quadrax inserts.  Those are very costly and difficult to terminate without having special tools, but sure do work well for emission reduction.  Jeff, I hope your situation is not so bad as to need those!

Good luck.  I hope that the relatively simple initial techniques are adequate for the task.  

73, Dale
WA9ENA 

   


-----Original Message-----
>From: Cortland Richmond <ka5s at earthlink.net>
>Sent: Mar 3, 2013 4:11 AM
>To: rfi at contesting.com
>Subject: Re: [RFI] RFI suppression cores for 147 MHz
>
>Listen to Dale; I've been to his shop (when he was still there) in Cedar 
>Rapids. Interesting days.
>
>The connector is typical of its type.  Be sure it is actually making 
>contact in the shielded receptacle and that the foil shield (you won't 
>find braid in a civilian product) all the way around and to a conductive 
>surface of the braid; I've seen off-the-shelf cable with connectors 
>assembled to the insulated side of a Mylar-aluminum shield.
>
>FWIW department; military stuff is orders of magnitude harder to do than 
>civilian. A military product I worked on a few years ago someone had 
>fondly and optimistically designed with Ethernet routed on 
>multi-conductor connectors (though using an otherwise well shielded 
>quadraxial cable).  They were repeatedly told not to -- and not just by me.
>
>The design had to be changed to shielded quadrax all the way down to the 
>card level, and the connector to MIL-38999 with quadrax inserts  
>(example: 
>http://eccochicago.com/wp-content/inventory_images/Amphenol%20Quadrax%20Contacts.png 
>).  Be warned.
>
>The router is another problem.  That one is a Class A device and 
>certified at an RF level three times higher than a Class B device meant 
>for residential use. Reference to "for residential use" in the 
>installation istructions is contradicted by the class for which it is 
>certifed both in the FCC-required wording and the EN 55022 Declatation 
>of COnfromity.
>
> From the installation instructions at
>ftp://downloads.netgear.com/files/FS116_IGprt_16Dec09.pdf :
>
>*Federal Communications Commission (FCC) Compliance Notice: Radio 
>Frequency Notice*
>This device complies with part 15 of the FCC Rules. Operation is subject 
>to the following two conditions:
>.  This device may not cause harmful interference.
>.  This device must accept any interference received, including 
>interference that may cause undesired operation.
>Note:  This equipment has been tested and found to comply with the 
>limits for a Class A digital device, pursuant to
>Part 15 of the FCC Rules.  These limits are designed to provide 
>reasonable protection against harmful interferences in
>a residential installation....
>
>*EN 55 022 Declaration of Conformance*
>This is to certify that the NETGEAR Model ProSafe^(TM) 16 Port 10/100 
>Switch with 8 Port PoE FS116P is shielded
>against the generation of radio interference in accordance with the 
>application of Council Directive 89/336/EEC,
>Article 4a.  Conformity is declared by the application of EN35 022 Class 
>A (CISPR 22).
>
>Cortland Richmond
>KA5S
>
>On 3/2/2013 1820, Jeff Stevens wrote:
>> Thanks to everyone who has contributed to the discussion on the use of
>> shielded twisted pair.  I'm interested in what folks think about connection
>> of the following devices in regard to providing a circumferential shield.
>> They are a fairly good representation of what is easily available 'off the
>> shelf' (and at reasonable cost) to the home user.
>
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