Some more items for Jim's list:
The main cause of "RF in the shack" is probably not the power amplifier
in its shielded enclosure, but faulty shielding in RF patch cables and
incorrect "ground" bonding between the major items of equipment
(transceiver, PA, ATU) on the operating desk.
So take this opportunity to give your station a thorough health check,
too.
7. Bond together the ground terminals of all the major items on the
operating desk. The important thing here is bonding them TOGETHER.
(Bonding to a safety ground is important too, but bonding them TOGETHER
should come first.)
8. Build or buy a clamp-on RF current meter, and USE it to verify that
various cables in the shack are not carrying undue levels of common-mode
RF current.
Easy home construction projects:
<http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm>
Product reviews - a 'Good Buy' and a 'Don't Buy' from MFJ:
<www.ifwtech.co.uk/g3sek/clamp-on/mfj-reviews.pdf>
As a very rough guide to levels of common-mode RF currents in the shack,
1-10mA is probably OK but levels approaching 100mA should be
investigated - not because such levels are dangerous, but because they
indicate some kind of fault.
The first time you do this, check EVERY cable in the shack, including
those that you wouldn't imagine to be carrying high levels of RF
current. You may be surprised!
9. Bad shield connections in PL259s are by far the most common source of
failures, so inspect every PL259 in the entire station. Check the solder
joints in classic (MIL-pattern) PL259s, and re-work or replace any that
have been assembled using short-cut methods. For guaranteed shielding
integrity, trust only PL259s that have been properly soldered with a big
iron - or better still, move toward replacing them with modern crimp or
compression-sleeve variants. Crimp connectors can be very reliable, but
*only* if assembled using the correct cable prep and crimp tooling.
10. Investigate any other cable on which you can see unduly high levels
of common-mode RF current, and work toward eliminating those currents
using SERIOUS ferrite chokes - see (www.k9yc.com ,
www.karinya.net/g3txq/chokes and < http://tinyurl.com/rfchokes>. Don't
waste time with ineffective chokes using unknown ferrite cores, short
strings of beads, dust-iron cores (the wrong material for chokes) or
coils of cable with no ferrite at all.
After that thorough check, you may also find that you're hearing weak
signals better, and that your station is "healthier" than it has been
for a long time.
73 from Ian GM3SEK
>-----Original Message-----
>From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim
>Brown
>Sent: 02 August 2014 18:49
>To: amps@contesting.com
>Subject: Re: [Amps] Experience with Heart Pacemakers?
>
>On 8/2/2014 10:28 AM, George wrote:
>> What Pacemakers do best with most amps?
>
>I know nothing about Pacemakers or their RF susceptibility, but I do
>know a bit about RFI. As far as I know, there are two issues. One is
the
>leakage magnetic flux from the power transformer. The other is radiated
>RF. Unless the amp is a poorly shielded POS, all the RF gets radiated
by
>your antennas, with some possible leakage from el-cheapo coax and
>connectors, and connectors poorly installed.
>
>So the key issues are:
>
>1) locate the power supply as far from where you will operate as
>possible. This may mean using a different power amp.
>
>2) eliminate the use of any antennas that put a lot of RF in your
shack.
>This generally means use only well-behaved beams and dipoles fed with
>coax, again as far from the shack as practical.
>
>3) go through EVERYTHING in the RF path between your power amp and
>your
>antennas and make sure that it is well shielded, all the coax has a
>beefy copper braid shield, that all connectors are first quality
>Amphenols, all are properly installed, and there are no el-cheapo junk
>connectors, barrels, adapters, etc. in line.
>
>4) study the construction of your power amp to verify that it is,
>indeed, well shielded. Are all cables either shielded or properly
>bypassed? Do shields go directly to the chassis where they enter the
>amp? (They must for shielding to work).
>
>5) Find out from the manufacturer of the pacemaker the specific range
of
>frequencies to which it has sensitivity.
>
>73, Jim K9YC
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