Hi Jeff,
Micro arcing can be excited by just a few volts of RF. While micro arcing
probably is n't a fire risk, micro arcing radiates low level phase noise
on transmitted signals. This is can cause a serious interference
problem to nearby receivers such as neighboring hams or co-located
receivers such an in-band receiver in a contest station.
I personally experienced these problems with megawatt transmitters.
In one instance, a massive radial system for a one mile long of array of
HF phased verticals had to be completely replaced because it generated an
elevated noise floor that degraded the performance of the HF over the
horizon radar. In another case a poorly engineered, badly installed and
inadequately maintained radial system for a 500 kw VLF system caused
severe television interference to neighbors that forced premature site closure.
73
Frank
W3LPL
----- Original Message -----
From: "Jeff Blaine" <KeepWalking188@ac0c.com>
To: topband@contesting.com
Sent: Saturday, November 7, 2020 5:43:25 AM
Subject: Re: Topband: OT - Bonding Radials at Intersections
I of course defer to Frank's expertise here. But after thinking about
this for a couple of hours, I'm trying to wrap my head around this arc
risk concept as well. It's interesting and I toss this comment out
because my two sets of 4sq don't have a single cross-bonded wire
anywhere - all the ground structure is ground mounted, with overlapping
wires literally all over the place. And despite that, the do seem to
work more or less OK, as far as I can tell.
I guess my thinking is list this... All those radial wires are laying
out on the ground. So they are at least connected at some point, at a
DC level, assuming your talking about something conventional like a 4SQ.
Of course, we are talking about AC here, so I will agree that maybe the
conditions could exist where - with just the right configuration between
the two radials - that some larger than expected voltage differential
may be present. Given how low Q a 4SQ is, how current is split between
multiple elements, my gut feeling is that the excitation voltages are
pretty mild even if you have your 1500W source right there at the 4SQ
input.
And on top of that, the wires are laying on the ground, right? The
radials are in more or less intimate contact with the ground, so I would
expect there to exist leakage resistance between adjacent conductors (if
they are bare). And if they are perfectly insulated, this being AC,
that means there is going to be some amount of cap coupling between
adjacent wires and to the ground. With all of that R&C spread out all
over the field, I would certainly think this conspires to work against
the probability that any two optimally aligned individual crossing
conductors would provide a condition sufficient to support an arc, and
that if so, it would survive long enough to cause a fire.
It's very very very dry here in the summer and again in the winter. So
fire risk is something we keep a real close eye on. Then again, out here
in the Midwest some of us do a lot of IL-advised things because they
seem to work and of course because laziness is a BIG part of the
calculation. ha ha. Maybe we have been taking a walk on the wild side
without realizing it. Hope not because I sure don't want to go try to
rectify this poor decision 3 years post installation! Say it ain't so!
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 11/6/20 10:59 PM, donovanf@erols.com wrote:
> Always beware of any communication that begins "with all due respect"
>
> ----- Original Message -----
>
> From: "Wes" <wes_n7ws@triconet.org>
> To: topband@contesting.com
> Sent: Saturday, November 7, 2020 4:49:23 AM
> Subject: Re: Topband: OT - Bonding Radials at Intersections
>
> With all due respect, I must ask, how many megawatts are you guys running?
>
> Wes N7WS
>
>
> On 11/6/2020 3:26 PM, donovanf@erols.com wrote:
>> Hi Carl,
>>
>>
>> If the insulation breaks down they will arc, potentially causing a fire
>>
>>
>> 73
>> Frank
>> W3LPL
>>
>> On 11/6/2020 4:27 PM, Richard (Rick) Karlquist wrote:
>>> On 11/6/2020 1:10 PM, Carl Clawson wrote:
>>>> Frank,
>>>>
>>>> “Must” is a strong word. What goes wrong if you cross them?
>>>>
>>>> 73, Carl WS7L
>>>>
>>> Also, if insulated wires are used for radials that cross
>>> over each other, is that to be treated differently than bare
>>> metal wires that cross over each other and touch
>>> so as to have electrical connectivity?
>>>
>>> Does it matter if cross over radials are soldered at the
>>> crossovers, so as to prevent parasitic "diodes".
>>>
>>> For whatever weird reason, the price of insulated wire is
>>> nearly always lower than the equivalent bare wire. And
>>> Romex sells for less than the equivalent individual wires.
>>>
>>> Rick N6RK
>>> _________________
>>> Searchable Archives:http://www.contesting.com/_topband - Topband
>>> Reflector
>
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