Jim, Frank and others,
I have read with interest the thread on RF Flooding with interest as I have
had some of the symptoms described: "rise up floor noise
level about 60 khz on each side from main harmonic frequency.".
When listening on the 2nd radio, if I transmit on the first radio the noise
floor rises to the point where strong signals are difficult to copy amid
the increased noise.
I have some questions about debugging a possible RF Flooding scenario:
- The problem for me seems to occur only when using the amplifier. I can
power up to 100W using batteries but do not have a way to turn off the
mains at high power to easily eliminate other household wall warts. Is
there a way to simulate the same effect using lower power? Will closer
spacing or other frequencies reflect the problem more obviously so that I
might find it using 100W?
- Can you recommend any ways to utilize a broadband SDR such as an SDRPlay
to help determine if the issue is RF Flooding or simply typical harmonic
inter-station interference? Or any tips on using a KX2 handheld to walk
around "sniffing" for problematic devices or wall warts?
- Seemingly RF Flooding would not be helped much by stubs or bandpass
filters if the desired transmitted signal is interacting with a wall wart.
Thus it would seem that adding or removing stubs meant to filter the second
harmonic would not be likely to reduce RF flooding from a wall wart that
was being excited by the desired signal. Is this intuition correct?
- How does one differentiate between transmitted broadband phase noise and
RF flooding? Are there signal characteristics that can help differentiate
the two?
- I generally use LMR400 Flex coax in the shack and LMR400 once the coax
gets outside. How much impact is the leakage in the shielding of this coax
likely to have on my inter-station interference? At present, six runs of
it run in a bundle along the ceiling from the output of the amplifier in
the operating position over to the place where the coax leaves the shack.
Once outside the shack, each line has a loop in it and all of the loops
sit adjacent to one another near the box/panel where the coax enters the
building.
Any thoughts or advice would be much appreciated.
73,
Matt NQ6N
On Fri, Sep 15, 2017 at 2:11 PM, Jim Brown <jim@audiosystemsgroup.com>
wrote:
> On 9/15/2017 11:20 AM, donovanf@starpower.net wrote:
>
>> Your 1/2 mile RF flooding RFI experience is similar to mine. I've only
>> been able to resolve a few RF flooding RFI cases from nearby homes.
>> In each case the problem was a wall wart, especially Apple iPhone
>> and iPad wall warts.
>>
>
> In my own home, I've replaced all SMPS wall warts with vintage linear wall
> warts. Those vintage supplies are often found in second hand stores and at
> hamfests for a buck or so each. In the "killing RX Noise" applications
> note, I outline methods for doing this that can be implemented if you can
> first make a survey of the offending home, then return with a suitable
> replacement. An important part of this is to learn how by doing it in your
> own home first.
>
> Also -- ferrite chokes on wiring that receives our TX RF and re-radiates
> the distortion can also help, and are minimally invasive.
>
> And thank you very much for publishing what you've learned on this issue.
> I incorporated your work, with credit, into both the 2-part NCJ article and
> my talks at ham events. Visiting with N6TV at W7RN last fall during the
> last hours of CW SS, I observed the problem in Bob's headphones. Your
> posting of that was key to my identifying it.
>
> One of the worst unresolvable problems is smoke detectors permanently
>> connected to AC power wiring. I can correct them in my own home,
>> but for obvious reasons not in neighboring homes.
>>
>
> The "home security" and aftermarket telephone industries have long been
> among the most backward of all with respect to good engineering practice.
>
> 73, Jim
>
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