Spot on, Kelly-
That's why in the microwave radio world, for frequencies above 18GHz, we
built radios with the transmitter output bolted right onto the back of the
antenna feedhorn for zero transmission line losses. Of course the RX low
noise amp was at the same location.
73,
Steve
N6SJ
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
ve4xt@mymts.net
Sent: Monday, September 26, 2016 8:39 AM
To: jimlux
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Legal Power measurement Discussion
Further to Jim's point,
Even if you accept that you must measure at the output connector of your
amp, the rules certainly do not mandate an accepted norm of station
construction.
Just because most people have their amps beside their radios doesn't mean
you can't put your amp as close to the feedpoint as possible.
If you figure you have combined system losses of, say, 3dB between the shack
and base of the tower, and run an amp that takes 50 watts drive to reach
1,500 watts, what's to stop you from running 100 watts drive inside the
shack to have 50 watts appear at the amp input? And thus, 1,500 watts going
up the tower.
What if you could engineer a box that bolts a 1,500-watt amp to the tower
five feet from your 6-el 20m yagi? A 10-foot run of coax will have minimal
loss.
You might be an alligator, but are you breaking any law? (For the purposes
of discussion, let's set aside practicality issues, given it's largely
academic at this point.)
What if that same box equalized the advantage on receive, preamplifying
enough to overcome feedline losses on receive? Or maybe that amp is feeding
is a 4-el 80, and you're using beverages for receive anyway.
73, kelly, ve4xt
Sent from my iPad
> On Sep 26, 2016, at 10:04 AM, jimlux <jimlux@earthlink.net> wrote:
>
>> On 9/26/16 7:33 AM, James Wolf wrote:
>> So, if I removed the output connector on my amplifier and wired the
>> coax directly to the output relay inside, does the coax now become
>> part of the amplifier?
>>
>
> It could be.. consider an absurd straw man - you've got your transmitter
and coax inside a long airconditioning duct out to the antenna, so the only
"connector" is a the end of the duct. Your transmitter "box" is 2x2x100 ft.
>
> What about coax inside a metal raceway (conduit).
>
> So you get into this rats nest of "where is the boundary line?"... Part 97
is silent on this essential detail.
>
> Ultimately, I suspect that if you're not "radiating" too much power, the
FCC cares not where you draw the line - they show up outside your property
with a field strength meter, not a magic probe that can see inside the coax.
>
> For another oddball case: consider a resonant compact loop with the loop
being part of the PA tank. This is real common in consumer equipment.. the
L in the tank is also the radiator.
>
>
>> Jim - KR9U
>>
>>>>> Jim's right: it's not clear at all what Part 97.313 really means.
>>>>> It
>> provides no standard for measurement and no indication where the
>> measurements should be taken. You can't really say "Well, it's
>> obvious they mean at the transmitter."
>>
>>
>>
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>>
>>
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