something is acting up on my end... my last response came through "blank".
Here's another try: ************************************************************************* There is no unshielded CAT 7/7a... at lower classes the cable/connectors may be chosen as UTP or STP... Cat 7 and above is DOUBLE shielded. Overall shield (braid) and shield per pair (aluminum tape). Any device putting out RFI as common mode are NOT in spec.... Whether they can be "fixed" or not has a lot to do with what "mistake" in design caused the problem in the first place. That has to be determined by device. Depending on the cause of the RF generation, there are a number of ways to mitigate/eliminate the problem... Shielded cable is only ONE possible component in the overall solution. A non-inclusive list of causes: Badly designed and/or shielded switch mode power supply (wall wart OR internal). A wall wart can radiate via the DC cord to the device and/or send the signal into the device via the DC cable and then radiate via the chassis or signal cables.. USUALLY internal PSs are adequately shielded... but poor input filters or none at all can let the bad stuff through. Wireless radios that are improperly designed or shielded can also be the culprit. Not having a separate logical and chassis ground can be a problem... Crappy fans... (best devices have properly designed passive cooling). Lots of ways for a bad design to create noise. Shielded cables work best in my experience when you can create an isolated chassis (or supplemental Faraday cage type superior to the chassis (or internal to a plastic case) where the outer shield of the cable and connector housing can be connected in one continuous shield around the device(s) and the cable, etc, etc... The benefit to CAT 7/7a would be the double shielding and the superior connector termination and housings... make for easier continuous shield external connections to drain/ground, et al. Typically, it would be cheaper/more reliable to buy a properly designed device in the first place... Note: there is a CAT 8 draft spec out now... CAT 7(+) would make an excellent 4 circuit control wire for remotes and the like since it has shield per pair... CAT 7(a) cable, connectors, and tooling is insanely expensive by comparison to 5/5e and even 6(+) ______________________ Clay Autery, KG5LKV MONTAC Enterprises (318) 518-1389 On 3/7/2016 4:48 PM, Jim Brown wrote: > On Mon,3/7/2016 11:07 AM, Clay Autery wrote: >> I'm not sure what the RFI issue would be that would require CAT 7... >> Tell me what you're trying to fix and I can offer more info... > > There are well known issues with equipment using one of the wired > Ethernet standard rates (have forgotten which one) generating carriers > at several frequencies in the HF bands and on 6M. I'm primarily a CW > guy, so the ones I run into are around 14030, 21052, the low end of > 10M, the low end of 6M, and a couple of frequencies on 30M. These > signals are radiated as a common mode signal, and I've been told that > properly terminated shielded CAT5/6/7 eliminates it. Properly > terminated means both in the cable-mounted plug and the > equipment-mounted jack. I've also experienced broadband hash on 2M > with a talkie within a foot or two of unshielded CAT5/6, including > Belden's excellent Mediatwist cable. > > In addition to its use for wired Ethernet, unshielded CAT5/6/7 is > quite useful in noise sensitive circuits because of its high twist > ratio. As with Ethernet, twisted pairs reject noise and crosstalk ONLY > when wired with one pair per circuit -- that is, or and or/blk as a > circuit, bn and bn/blk as a circuit, and so on. > > 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
