[NLRS] CQWW VHF AC0RA/R Rover HP

Tue Jul 24 00:11:17 EDT 2018

First of all, congrats to Wyatt and Dave. That is a very good score and one that will stand a long time.

It is good to be concerned about the RF exposure, but it is easy to put that concern to bed with calculations. 

The FCC exposure limits are 1mW/cm^2 averaged over 6 minutes on 50 MHz and 144 MHz. For CW operation a kW at the antenna, probably a bit less in AC0RA’s case, will be about 200W averaged over 6 minutes. CW duty cycle is 40% and in a contest, about 50% is spent transmitting and 50% receiving. So there is 200W average power to the antenna. A 5 element Yagi will have a gain of about 11.5 dBi. If the antenna is 20 ft high and 10 ft horizontally from the antenna, that puts the driver at about 23ft from the antenna.  There are several RF exposure calculators on the web and plugging the above numbers into the calculators, one gets about 0.5mW/cm^2, half of the allowed exposure. The RF calculator calculates the power density in the main beam, the driver is off-axis by quite a bit, plus, teh beam is not always pointed at the driver, so drop these numbers by more. Reflections get complicated, so one really needs to do a detailed computational electromagnetic analysis, one of the NEC or MiniNEC programs is probably adequate for this. The detailed analysis should include the structure of the truck including the roof which provides some shielding, to get more precise values, but I think more precise calculations will still be below the maximum permissible exposure. Wyatt probably has considered all of this. 

The 1mW/cm^2 exposure limit is for controlled exposure (essential to those knowledgeable in RF and the specific installation), the uncontrolled limits are lower, but in most rover locations, including mobile applications there are few RF onlookers. 

One can do the two meter calculations in a similar fashion.  

See you in Wichita. - Duffey KK6MC

James Duffey KK6MC
Cedar Crest NM

> On Jul 23, 2018, at 20:10, Dr. Gerald N. Johnson <geraldj at netins.net> wrote:
> 
> 
> 
> With the small distance to rover antennas without a 40' tower, I'd be concerned that the RF exposure is unhealthy with KW amplifiers.
> 
> Were the roves in Iowa and near Iowa? I didn't turn a rig on during the contest, not being a fan of CQ magazine.
> 
> 73, Jerry, K0CQ
> 
>> On 7/23/2018 9:06 PM, Jon Platt via NLRS wrote:
>> 
>> 
>> 
>> Nice job Wyatt.  KW rovers, yeah!
>> 
>> Looking forward to hearing some war stories !
>> 
>> 73, Jon
>> W0ZQ
>> 
>> 
>> -----Original Message-----
>> From: Wyatt Dirks<dirkswyatt10 at gmail.com>
>> To: nlrs<nlrs at mailman.qth.net>
>> Sent: Mon, Jul 23, 2018 8:38 pm
>> Subject: [NLRS] CQWW VHF AC0RA/R Rover HP
>> 
>> 
>> 
>>                     CQ Worldwide VHF Contest
>> 
>> Call: AC0RA/R
>> Operator(s): AC0RA KG5CCI
>> Station: AC0RA/R
>> 
>> Class: Rover HP
>> QTH:
>> Operating Time (hrs): 26.25
>> 
>> Summary:
>>  Band  QSOs  Mults
>> -------------------
>>     6:  606   350
>>   2:   81    68
>> -------------------
>> Total:  687   418  Total Score = 321,442
>> 
>> Club:
>> 
>> Comments:
>> 
>> Conditions for the contest were great on 6m overall. Saturday 6m opening
>> seemed
>> very wide spread but not many qsos to be had. Sunday when the band opened my
>> best run was 190 qsos in 1 hour and 6 minutes reaching well over 200 rate
>> for a
>> while within that hour. 2m had no enhancement that I noticed and pretty low
>> activity.
>> 
>> Digi qso totals
>> 
>> 36 on 6m msk144
>> 25 on 6m ft8
>> 17 on 2m msk144
>> 
>> Using /r in wsjtx is a major issue. We attempted many many more ft8 qsos on
>> 6m
>> but couldn't complete do to /r. The contest mode issue is minor compared to
>> the
>> /r problem. Interestingly enough we had zero problems with contest mode or
>> using
>> /r on msk144. Obviously this is because guys working msk144 have a clue.
>> 
>> The rover consisted of 5 element 6m yagi at 20ft and 7 element 2m yagi at
>> 18ft.
>> as well as a 3 element 6m yagi at 12ft and 3 element 2m yagi at 10ft. The
>> smaller yagis were going to be used for in motion ops but we more less gave
>> up
>> because ft8 was the only activity and it was far to frustrating to work ft8.
>> Used an IC7300 for 6m and an IC910 for 2m with kw amps on each band. Lots
>> and
>> lots of improvements need to be made with the rover before next years
>> contest.
>> 
>> Also would like to note I didn't sleep the entire contest. I was either
>> driving
>> or operating. Dave slept a little bit while I driving but not much. Our goal
>> going into contest was to give it our best effort to break record which is
>> about
>> 220k. We did go qrt with 45 minutes left of the contest when KC0SKM/r
>> pulled up
>> and we talked till the end of contest.
>> 
>> I'd like to thanks everyone for the qsos and especially Dave, KG5CCI for
>> joining
>> me for this truly amazing contest.
>> 
>> 73 Wyatt
>> AC0RA
>> 
>> 
>> Posted using 3830 Score Submittal Forms at: http://www.3830scores.com/
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