eHam

eHam Forums => RFI / EMI => Topic started by: KA4NMA on December 06, 2017, 10:41:28 PM



Title: Anybody know about these(
Post by: KA4NMA on December 06, 2017, 10:41:28 PM
Anybody know about these? Are the good for hf rfi?

 https://www.amazon.com/gp/aw/d/B0757H1SBZ/ref=mp_s_a_1_6?ie=UTF8&qid=1512628652&sr=8-6&pi=AC_SX236_SY340_QL65&keywords=50+ferrite+core+rfi&dpPl=1&dpID=51ANEK3rFRL&ref=plSrch

Or

https://www.amazon.com/gp/aw/d/B01DEYONX8/ref=mp_s_a_1_11?ie=UTF8&qid=1512628652&sr=8-11&pi=AC_SX236_SY340_QL65&keywords=50+ferrite+core+rfi

Randy Ka4nma




Title: RE: Anybody know about these(
Post by: AE5GT on December 07, 2017, 08:05:25 AM
The chart provided shows 65 -90 ohms at upper HF , up to 200 ohms at 100 Mhz .  So based on that i would use these on upper HF to low VHF, Ok  for computer cable suppression , not so great for switch mode supplies operating in the low HF . Probably useless for supplies in the khz region. 


Title: RE: Anybody know about these(
Post by: AB4ZT on December 11, 2017, 02:42:25 PM
Hello Randy.  I assume (perhaps wrongly) that this is a follow-up from your previous post regarding s-8 noise, etc.  Please know that RFI to YOUR receiver must be attacked at the source.  Chokes on your antenna cable will not help.  The exception is a single source of local RFI, in which case an active noise canceler such as the MFJ-1026 may be effective.  But that is neither a cheap solution nor one for multiple offending sources, which sounds like it could be the case given your location:  the church may have any number of noise sources such as cheap switching power supplies, security lights, etc.  This is a roundabout way of saying ferrite beads on your radio cable won't help.  On top of that, the antenna you are using I assume is located either indoors of very near the apartment, right next to the offending devices.  By the way, that antenna is pretty close to the last of the last resorts to get on the air.  So, what can you do?

 - Get a simple wire antenna up as high and far away from the apartment as you can

 - Get the church to cooperate with you, and try and locate the offending devices - maybe there are one or two that are causing most of the problem, and if you fix (change) those, that may make the situation much more tolerable - do you know how to properly substitute switching supplies (by voltage, current, and polarity)?

 - Best scenario - the offending device is in YOUR apartment.  Look around for devices you have (including routers, cable boxes, etc) that are powered by small power supplies.  Unplug them one by one...you may get lucky (I should have listed this first).

Wow, tough news, yes? But the fact is if you do not locate the source of the RFI, your situation is rather bleak.  Success depends on knowledge.  A good starting point is here:

http://www.arrl.org/radio-frequency-interference-rfi (http://www.arrl.org/radio-frequency-interference-rfi)

73,

Richard, AB4ZT