[Ham-Mac] RFI getting into computer

[Steve Hellyer]

Hi Richard,

I hope you understand that it will always be a battle with an antenna  
so close to your computer.  Actually I worry more about you own  
personal exposure to such high RF radiation levels over a prolonged  
time!!

Don't kid yourself 30 watts on PSK is a lot.  Typical transceiver  
today has a fairly low duty cycle. PSK, RTTY and digital modes work  
your finals very hard.  I only use 25 watts on my Kenwood which is  
rated for 100w peak.  These digital AFSK mode send without pauses  
which you would find in voice or CW.

Some of the Macs/Apple monitors, but not all, have touch sensitive  
switches.  My old G4 cube had one.  They are more susceptible to  
strong RF than a physical switch.  Like a laptop trackpad they  
measure capacitance changes.  That's how they tell if your finger is  
one them.  Strong RF will change the capacitance field make it think  
you put your finder on the button.  Hence why you Mac turns off or  
goes to sleep (Depending on your systems settings).

iMac G5 and iMac Intel Core Duo have a push button switch.  So you  
should be ok.

Todd is correct. All plastics have an RF "paint" sprayed on them but  
this is to minimize RF getting out of the computer not really design  
to prevent heavy RF getting in.  There is no manufacture of computers  
that test strong RF signal like 30 watts or more at 10 feet away.  
Heck a wireless base station or card uses less than 50 Milliwatts.

RF is getting into all parts of your computer. The amount depends on  
many variables including, as you noted, its position relative to your  
antenna.  At the right TX frequency and TX pattern you could actually  
be interfering with the computer CPU, memory, power supply, hard  
drives, USB hubs and more. I would use a separate ground, if  
possible, for your antenna and liberal use of Ferrite cores on all  
monitor, power and audio cables to reduce RF getting into electrical.  
Would not put them on USB/Firewire as that seems to cause problem  
with their ability to transfer data.

You are going to have to be quite forgiving of all electrical  
equipment in your close proximity and take some time to work it out.  
Even the change in TX frequency, band, SWR of your antenna will have  
different effects.  And again I will stress be careful of your own  
personal exposure to high and prolonged levels RF.

Looking forward to hearing your experiences with the new computer.

Steve
VA3SPH


On 6-Jun-06, at 11:18 AM, Richard Hemingway wrote:

> Thanks to all the replied.  I have ordered the iMac and I guess I  
> will see how it works.  I'm really not grounded at all.  Just an  
> electrical ground to the third wire outlet.  I do have a  
> counterbalance wire on he antenna.
>
> I have moved the antenna as far away as I can and have no other  
> option on that (How I wish I had the tower I had before I retired -  
> with a Sommer seven band antenna)!! I haven't tried to tune on 6  
> meters yet, I will try it.
>
> The LCD studio display (15") does not have a power switch on it.  
> Before I got it positioned pretty well, RF would turn on the Mac G5  
> if it was plugged in.  I don't have that trouble now, especially at  
> low power.
>
> I really appreciate the help.
>
> 73, Duck, N5XRD
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