Howard,
Since your use of a quote from my posting on power supplies started the
whole ladder line thread, I thought I should weigh in with a few comments.
First, we must keep in mind that "lower emissions" does not mean "NO
emissions". I still maintain that the SS-30 series of power supplies is
an excellent performer with respect to EMI, as reported by ARRL lab
testing. But, like anything else in the techncial realm, there are many
variables and you found a major one with your station setup using the
ladder line. Just curious: how close was the power supply to the line?
Now, here is where the fire and flames will begin. Howard, you kept the
ladder line and changed out the power supply. I would have trashed the
line and kept the supply. Here's why:
1. Retaining use of ladder line still leaves you vulnerable to other
noise sources. Jim Brown's (K9YC) postings clearly discuss the issues
with the use of open line from an RFI perspective.
2. Retaining use of ladder line (or any other form of open wire feeders)
leaves you very vulnerable to lightning damage of the worst kind. It even
raises the issue of personal safety. Let me ask: How many people on this
reflector who use wire feeders of any type have any form of lightning
protection on those feeders?
Thanks to E-Pay, I do have a pair of lightning protectors for wire
feeders. They are US Gov't surplus (NOS) and were once part of a rhombic
antenna kit. I myself do not use any wire feeders at this time, but I am
thinking about erecting a 132 foot flat top in the near future. It will
be fed with wire feeders and those protectors will be at the bottom end of
those feeders - right above the remotely located tuner that will be used
with that antenna. There will be coax between my shack and that tuner.
(Fixed rule in my shack: no unprotected lines shall enter or leave the
shack. All RF transmission shall be via coaxial cable only. Rotator and
remote switch lines shall be protected with appropriate devices made for
the task. The same is true for telephone and video lines.)
I love classic rigs and accessories, and the Johnson Matchbox tuner is
truly one of those. I own the smaller (275 watt) Matchbox, but its only
use for me is Field Day or portable operations. It will never see wire
feeders in my shack. Anyway, before lighting off the flares and rockets
in my direction, please consider what could happen if your antenna and/or
wire feeders were to take a direct lightning attachment. Can you envision
your shack resembling the contents of a bag of Kingsford's product? As
someone who took 2 direct hits in 2 years (and have the scorched and
exploded antennas, "modified" coax, and welded remote switch relays to
prove it), that thought enters my mind a lot.
If you do not have lightning protection on your open feeders, then I
suggest, at a minimum, you have some sort of reliable scheme for hard
grounding them when not in use and/or disconnecting them from the entry to
the shack, when not in use. If you don't want to run around and mess with
lots of big clips to make "kluge" connections, consider use of Kilovac (or
equivalent) high voltage relays to handle the switching chores for you.
Finally, someone else has already said this, but it bears repeating:
virtually every electronic device today uses a switching power supply in
one way or another. That's because linear power supplies can not meet the
"Green" efficiency requirements and also because iron core transfomers
wound with lots of copper wire are too expensive. Those of you on the
list who have not had RFI problems from switchers should consider
yourselves as fortunate. However, your luck may not last forever. Note
that practitioners of the EMC art, such as W1RFI and K9YC, make frequent
mention (and use) of common mode chokes and balancing of wire pairs to
minimize RFI effects. It is very difficult to do those tricks with wire
feeders (especially the common mode choking), so keep all of that in mind
when laying out your station plan. I operate 160m thru 70cm, with plans
to expand into the 902 MHz and 1290 MHz bands soon. Examination of
current coax cable catalogs will show you that the manufacturers have come
a long way in reducing cable losses. I presently have 250 feet of LMR-400
in service on MF and HF, with more than 100 feet per run of either LMR-400
or LMR-600 for 6m, 2m, 1.25m, and 70cm applications. I will be going to
hardline as I move above 70cm. Take a look at RG-6/U coax as used by the
CATV industry. Yes, It has plenty of loss up at 700 MHz (with TV channel
51, now the "top" over-the-air channel in many markets, being just below
700 MHz), but that loss is easily compensated for by use of inexpensive
pre-amps or line amplifiers.
Putting on the Nomex suit ...
73, Dale
WA9ENA
Howard Lester <howard220@gmail.com>
Sent by: rfi-bounces@contesting.com
10/19/2010 10:35 AM
To
RFI List <rfi@contesting.com>
cc
Subject
Re: [RFI] Noisy or Quiet Power Supplies?
On Sat, Oct 16, 2010 at 9:54 PM, Dale Svetanoff
<svetanoff@earthlink.net>wrote:
> I have been running the Astron SS-30M for several years now with NO
> problems whatever. (See QST back in 2002 - can't recall the issue - for
a
> review of the Astron, and other, switching power supplies. The ARRL did
an
> excellent job of testing several popular models - most of which are
still
> available. Read the reviews then buy. That's why I bought the Astron;
it
> was the lowest noise unit they tested.)
>
> Based on that QST review I bought the same SS-30M for my new FT-950. I
was
hearing noise every so-many KHz up and down all the bands and wondered if
it
was the power supply. I phoned the dealer (KJI Electronics), and Gene
right
off asked me if I was feeding my antenna with ladder line. I replied "Yes,
and it runs through the wall and connects directly to the transmatch on my
desk." He said that was the problem. If I was running coax, he said, I
wouldn't have that noise. So I exchanged it for the old fashioned
heavyweight RM-35M and I have no noise issues with it.
Howard N7SO
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