There are three problems with the use of ultrasonic dishes:
1. They give false negatives. If an arc were taking place on the top of an
insulator, its ultrasonic noise would be blocked in the direction of ground and
thus not heard.
2. They give false positives. Corona discharge rarely causes RFI, but it can
and does generate ultrasonic noise.
3. There is no time-domain correlation between heard ultrasonic noises and
actual RFI to specific stations.
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Don Kirk
Sent: Wednesday, January 17, 2018 8:42 AM
To: Dave Cole (NK7Z)
Cc: RFI
Subject: Re: [RFI] Noise location tools
I agree with Dave, an audio dish would be the last thing I would buy (lowest
priority item). A problem I found while working with the local power company
that had an ultrasonic dish is that we could detect arcing on every pole we
checked, but out of all the poles we checked there was only one pole that was
the root cause of the RFI I was hearing at my house 1.1 miles away.
The most important feature I have found on any of my portable radio direction
finding systems (HF or VHF) that I use for tracking down RFI is the ability to
throw in a lot of attenuation when I get close to the source. If you get close
to the source and the signal is full strength even on the nulls of the antenna,
there is then no way you can do additional direction finding.
Don (wd8dsb)
On Wed, Jan 17, 2018 at 8:23 AM, Dave Cole (NK7Z) <dave@nk7z.net> wrote:
> Hello Mike,
>
> No need for the dish, it just locates arcing, and that is the Power
> companies job. Across the two years I had a dish, I think I used it
> once or twice.
>
> Better you save your bucks and build a loop with the saved cash. You
> will get a lot more use out of the loop than the dish.
>
> 73s and thanks,
> Dave
> NK7Z
> http://www.nk7z.net
>
> On 01/16/2018 08:36 PM, W0MU Mike Fatchett wrote:
>
>> Thanks all!
>>
>> Other than the ultra sonic dish I have most of the other pieces parts.
>>
>> Appreciate all the links and hints too!
>>
>> W0MU
>>
>>
>> On 1/16/2018 9:17 PM, Dave Cole (NK7Z) wrote:
>>
>>> Hi,
>>> See:
>>>
>>> http://nk7z.net/rfi-now-house-cleaning/
>>>
>>> for a three part series on how I managed to calm down my RFI
>>> environment. Also see:
>>>
>>> http://nk7z.net/sdr-rfi-survey-p1/
>>>
>>> for a tool to characterize your RFI.
>>>
>>> 73s and thanks,
>>> Dave
>>> NK7Z
>>> http://www.nk7z.net
>>>
>>> On 01/16/2018 11:39 AM, W0MU Mike Fatchett wrote:
>>>
>>>> What are people using for noise sniffing? I saw the MFJ dish but I
>>>> try to avoid their stuff.
>>>>
>>>> I know there is no one perfect tool.
>>>>
>>>> W0MU
>>>>
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>>>>
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>>
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