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Re: [RFI] Recommend a Small Low-RFI Inverter?

To: Jim Brown <jim@audiosystemsgroup.com>
Subject: Re: [RFI] Recommend a Small Low-RFI Inverter?
From: "Kenneth G. Gordon" <kgordon2006@frontier.com>
Date: Sat, 30 Sep 2017 18:26:08 -0700
List-post: <mailto:rfi@contesting.com>
On 30 Sep 2017 at 16:53, Jim Brown wrote:

> On 9/30/2017 11:46 AM, Kenneth G. Gordon wrote:
> > Samlex, pure-sine-wave inverter. Get the model(s) which are specified as 
> > low or no RFI. I bought a 300 watt version (don't have the model number 
> > handy) and am very pleased with it.
> Hi Ken,
> I do NOT share your experience with these inverters. I bought Samlex's 
> smallest PST-series unit to power the logging computer for our 7QP 
> county mobile operation. I was able to make it quiet enough, but it 
> needed a LOT of ferrite cores  to do it.

I am amazed! In our case, we could have used the case of our Samlex for an 
antenna the 
noise output was so low. I wonder if the age of our respective units has 
anything to do with 

> Another member of our team 
> bought one of the bigger PST units, (maybe the 300W version) and we were 
> not able to make it quiet enough. The thing that makes it hard is that 
> the antennas are VERY close to the inverter, and any trash on the power 
> wiring roars into the antenna.

We also used my PST-300-12 for the past two Field Days, and none of us have 
ever even 
noticed whether or not it was on, but our antennas are a LONG ways from where 
it was 
being used too.

> Slide # 213 in the link below
> http://k9yc.com/KillingRXNoiseVisalia.pdf
> shows what I had to do to make the PST-120-12 quiet enough to use in the 
> mobile with a hamstick on the back. The top two chokes (the largest 
> ones) were not needed for 20M/40M in the mobile, but were needed to keep 
> the noise out of the 160M vertical about 30 ft from my operating desk at 
> home. The smaller chokes with 4-5 turns are for 40 and 20, the 
> single-turn clamp-ons are for 2M.

As I said, I am amazed. Truly. Our experiences with the Samlex are far 
different from yours. 
I wonder why?

> Noise is, of course, a matter of degree. We were operating from very 
> quiet places in the middle of nowhere, where the local noise is S1. If 
> you're using the inverter in an urban environment (or in a noisy 
> vehicle) where the noise level is S9+, you're less likely to hear the 
> noise from the inverter.

Our noise level at our FD sites was below S-1. 

I have personally only used it in a mobile to power some DF equipment. There 
was zero 
change in the noise level as measured by the NM-20B whether running on the 
Samlex or on 

When I would take my noise measurements, the car would be turned off, so that 
was not a 

I wonder what the difference is?

I'll contact the fellow here who made some exacting measurements and get his 
records to 
post here as soon as I can. The figure -76 dB is yeasting around in my memory, 
but I don't 
remember, at all, to what that applies.

As I said, twice, I am amazed at your results. Those are entirely strange in my 

Have you contacted Samlex about this? As I mentioned previously, they are 
designed to be used in ambulances, so they HAVE to be RFI-quiet.

It sounds to me as though further research is in order here.


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