Re: [TowerTalk] Grounding, portable generators, field day

[Jim Lux <jimlux@earthlink.net>]

At 04:13 PM 1/20/2005, K8RI on Tower Talk wrote:



> > At 12:18 PM 1/20/2005, Keith Dutson wrote:
> > > To me, the answer to your question(s) is simple.  FD grounds should be for
> > > RF.  It would be nice to have a safety grounding system with SPG,
> >
> > I don't think you need SPG in this application..
> >
> > And, I can't see why you should operate unsafely, with respect to AC 
> > power distribution. Just because you're at field day doesn't mean you 
> > don't have to meet various and sundry safety rules (such as RF exposure).
>
> When you can safely get within a few feet of a 75 or 40 meter dipole 
> running a KW safely and you might be running a tribander at 30 feet with a 
> 100 watts it's going to be pretty difficult to exceed any RF safety limits.

I think the RF safety issue might be more of a problem with VHF and UHF 
rigs.  There's that picture in QST last year with the whip antenna on the 
picnic table next to the operator, for instance.

There have also been people who run 4-squares at field day (that one had a 
picture on their website with plastic net fencing around the antennas for 
RF safety).

Since the typical field day station will have more than 1 transmitter 
operating simultaneously. I don't think the typical field day setup is 
going to fall into what the FCC calls "categorically exempt from routine 
station evaluation". The "safe harbor" values in OET65B page 3 probably 
assume single transmitter at a time.  If you're running 100W on 10 or 15, 
you'd also have to do an evaluation.

Another example is whether contesting operation can legitimately apply  the 
20% duty factor for "Conversational SSB" in Table 2, Page 14. (Especially 
if you fall asleep with your finger on the parrot <grin>)

Another antenna that might need some analysis (since it's not in the OET65B 
list) would be an inverted V for 80/75.  At FD, you might have the 
vertex/feed up at 40 feet but the ends of the dipole (where the E field is 
highest) might only be 10 feet off the ground.

So... the analysis for any of these antennas might be trivial, but you 
still have to do it, and you have to have the "artifact" to show that you 
did.  It might just be a worksheet in the back of OET65B or piece of paper 
with the (trivial) analysis on it (worst casing from the tables in OET65B, 
for instance), documenting the assumptions on duty factor and power.  If 
you spend more than 15 minutes on it, it's probably overkill.

Actually, though, I think electrical safety is more of an issue at field 
day than RF safety.  The comment about RF safety was more that just because 
you're at field day doesn't relieve you of all the usual safety rules.


By the way, as far as the assumption of field day running 100W goes (or 
even 5W), it's rumored that some big FD ops use a "specially calibrated" 
power meter. 


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