Hello Jim,
Am 25.09.2016 13:53, schrieb James Cowburn:
Also
are you okay if I share the excellent spreadsheet you sent me some
years ago? It's really useful
Was it the Excel sheet that i used to calculate the ERP from my kite
vertical antennas? Share it if you like.
The
Wifi is okay, it's the cheaply built BT router that is poorly shielded
and so picks up my 472khz signals through it's paper thin plastic
casing (prob because it has internal antennae) and this plays havoc
with the broadband signals which are in the MF band and superimposed
onto the phone line. I need a better shielded router with external
wifi antennae
Yes, that's an idea. Or, just if you like to know, you could try to
temporarily run the router on batteries to break the common mode
circuit, if this causes the problems. If it is running at 5V by an
external SMPS, replace that by a 12V accu with a 78S05, providing 5 V
DC. If this solves the problem, then you could use the supply together
with a big ferrite core with a high AL value and wind a few dozen turn
on it, using twisted pair cable for example. Before applying that
common mode choke, you could try to measure the common mode current by
using a ferrite current transformer and a scope. Then you see how
effective the common mode choke will be...
I've
tried putting them in shielded earthed metal boxes (biscuit tins!) with
no effect. (biscuits were nice though!). Similarly, stacked ferrite
toroids on the mains inputs and DC power out have had zero impact.
They both have a very bright blue LED on the power cable whereas older
units for my Dell D610/20 series did not have this "bauble" and were
much quieter, but also were lower rated at 60W or 90W as opposed to
these beasts which are around 120W to 150W, and run alarmingly warm at
times!
If it is no common mode
problem with the LAN cable i would try to switch a pi-network in front
of the power supply, on the 230V side. 2x 1 uF (e.g. WIMA MP3-X2
250VAC) and then a iron powder choke (e.g. T106-26) with many turns of
0.5mm cu wire, two windings, "anti-parallel".
I
actusally have a very good quality old mains supply filter unit built
like this, I'll dig that out and try it. I'd assumed it was just the
smpsu part radiating through the plastic casing and undoubtedly having
no filtering applied at the 19.5 output so the power lead to the laptop
acts as a great antenna!! The PSUs are sealed and I don't want to
open it if I can avoid it.
Hm yes, it could be like that. Another source of unwanted currents
could be over the AF cable connected to the soundcard. An isolation
transformer may identify and/or solve the problem. Worth to experiment
with all that stuff :-)
73, GL, Stefan
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