[TowerTalk] 4 square for 80

Mon Sep 26 08:19:05 EDT 2016

It can often be easy to forget that ultimately, the only arbiter of law that counts is the Supreme Court.

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." 

Interestingly, here's the Canadian rule on the matter:

The holder of an Amateur Radio Operator Certificate with Advanced Qualification is limited to a maximum transmitting power of:

(a) where expressed as direct-current input power, 1,000 W to the anode or collector circuit of the transmitter stage that supplies radio frequency energy to the antenna; or
(b) where expressed as radio frequency output power measured across an impedance-matched load,
(i) 2,250 W peak envelope power for transmitters that produce any type of single sideband emission, or
(ii) 750 W carrier power for transmitters that produce any other type of emission.

Notice how it doesn't force you to choose one measurement scheme over another? So we in Canada could choose (b), measure at the feedpoint (across an impedance-matched load), and be within the rules if we pumped down the feedline however much power it took to get a 750-watt carrier or 2,250-watt PEP SSB to the feedpoint.

73, kelly, ve4xt 

Sent from my iPad

> On Sep 26, 2016, at 6:03 AM, jimlux <jimlux at earthlink.net> wrote:
> 
>> On 9/25/16 10:38 PM, Guy Olinger K2AV wrote:
>> Tom, W8JI, put this up in an email, simply reading part 97. Note the
>> term "transmitter power". Power would be measured at the output of the
>> final amplifying stage. A transceiver and an amp would be considered a
>> two part transmitter.
> 
> 
> SO that's Tom's opinion, which I value and respect, but it's also not a statement from the FCC. Technology advances, interpretation of regulations changes as the technology changes. An active phased array with multiple transmitters into a combining/distributing network doesn't really fit the basic Part 97 model of "transmitter" to "antenna".
> 
> It's not like there's one place with a nice 50 ohm impedance to put a Bird power meter in the line.
> 
> And even then, if you had a transmitter with a output tuning network feeding a weird impedance antenna, measuring power could be challenging.
> 
> Or consider a system using Chierex or other clever schemes that use multiple transmitters to improve efficiency.
> 
> If I had a 4 square, and the FCC asked about my power, I'd be comfortable summing the powers at the 4 feed points as my answer.  I suspect that when it all gets right down to it, the FCC cares about ERP - that's what the interference issue would be from.
> 
> 
>> 
>> I know that someone once posted the result of a call to an FCC field
>> office with this question, but I can't find it. I remember that the
>> answer was "at the transmitter." Tom's logic below seems conclusive
>> based on the literal wording in part 97.
>> 
>> ------------------------------------------------
>> 
>> peter gerba wrote:
>> 
>>> Where is the 1500 watts we are limited to measured from ?  The output of
>>> the Amp ?
>> 
>> Section 97.313b covers this. "No station may transmit with a transmitter
>> power exceeding 1500 watts PEP."
>> 
>> Transmitter power. Not common point or feedline power.
>> 
>> Broadcast stations are assigned an ERP power, usually limited by field
>> strength in a direction(s) that bothers another station(s).
>> 
>> That seems clear.
>> 
>> 73 Tom
>> 
>> http://lists.contesting.com/pipermail/amps/1997-April/000735.html
>> 
>> -------------------------------------------------
>> 
>> 
>> 73, Guy K2AV
>> 
>>> On Sun, Sep 25, 2016 at 11:59 PM, jimlux <jimlux at earthlink.net> wrote:
>>>> On 9/25/16 5:53 PM, Guy Olinger wrote:
>>>> 
>>>> The 1.5 kW PEP is at the amplifier output.
>>>> 
>>>> That has been clarified with the FCC multiple times. Tuner, feedline,
>>>> antenna system losses are your problem. You are diminished by those
>>>> losses unless you either have no losses, or run illegally.
>>> 
>>> Interesting, can you point to an opinion letter or enforcement action that
>>> says this?
>>> 
>>>> The commercial measurement scheme does not apply to the amateur service
>>>> except for a couple bands where that particular band references
>>>> effective radiated power. 1.5 kW is not allowed on those amateur bands.
>>>> 
>>>> 73, Guy K2AV.
>>>> 
>>>> On Sun, Sep 25, 2016 at 7:07 PM, jimlux <jimlux at earthlink.net
>>>> <mailto:jimlux at earthlink.net>> wrote:
>>>> 
>>>>    On 9/25/16 12:05 PM, Guy Olinger wrote:
>>>> 
>>>>        On Sun, Sep 25, 2016 at 12:25 PM, Jim Brown
>>>>        <jim at audiosystemsgroup.com <mailto:jim at audiosystemsgroup.com>>
>>>> 
>>>>        wrote:
>>>> 
>>>>            On Sun,9/25/2016 6:49 AM, Steve London wrote:
>>>> 
>>>>            What problem(s) are we attempting to solve with chokes on
>>>>            the 4-square
>>>> 
>>>>                feedlines ?
>>>> 
>>>>                Noise.
>>>> 
>>>> 
>>>> 
>>>>        Noise, yes. Gotta give you that one, but the main reason for the
>>>>        4 square
>>>>        was TX gain, right? You do have listening antennas for 160 and
>>>>        80? So we
>>>>        have to worry about *loss*. Loss eats up gain from patterns.
>>>>        Loss eats up
>>>>        amplifier output. Your *system* gain past your transceiver is
>>>>        antenna gain
>>>>        + amplifier gain *** minus LOSSES ***.
>>>> 
>>>>        Diversion of power to miscellaneous conductor paths is almost
>>>>        universally
>>>>        lossy and never in directions and modes desired in our attempts at
>>>>        directional arrays.
>>>> 
>>>> 
>>>>    So measure your output power at the system interface to the
>>>>    "antenna".. put 1500 watts (total) into your 4 antennas: sum the
>>>>    powers at each element (including if you have phased them so you
>>>>    have a negative element).  That's what commercial broadcasters do,
>>>>    isn't it?
>>>> 
>>>>    The regulations don't say "amplifier output", they say
>>>>    "PEP (peak envelope power). The average power supplied to the antenna
>>>>    transmission line by a transmitter during one RF cycle at the crest of
>>>>    the modulation envelope taken under normal operating conditions. "
>>>>    "(b) No station may transmit with a transmitter power exceeding 1.5
>>>>    kW PEP. "
>>>> 
>>>>    If I define my "antenna transmission line" reference plane at the
>>>>    antenna feed points, I think that works.
>>>> 
>>>> 
>>>> 
>>>>    _______________________________________________
>>>> 
>>>> 
>>>> 
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