[UK-CONTEST] Power Limitations

Mon Jan 30 02:58:18 PST 2012

Hi Bob,

I think this discussion should go off-list if it goes further, but just 
to clarify a couple of points briefly:

Maybe my description was unclear - my suggestion was that you used the 
halo on transmit BUT a beam on receive. So you get all the receive gain 
you previously had on a 5-ele beam, but you don't use the gain of the 
beam when calculating your ERP, since you transmit through the halo 
instead, and make up for the lost TX gain with power. You very much 
don't take the beam down - you keep that up for receive, and add a halo 
just for transmit. This means the receive setup is absolutely identical 
to before, you've just added a separate transmit chain.

600w amps on 6m are quite common already - many HF linears (Yaesu 
Quadra, Icom PW1, Expert 1K-FA, Acom 1000, Elecraft KPA-500, ...) 
already cover 6m. Sure, I'd prefer not to have to cart one along to the 
contest site every week, but if it gave us an advantage within the 
rules, I'd do it in a moment.

My choice of band was of course not accidental; 6m is the easiest one to 
make the numbers work, but on 2m it's not vastly different - a 9-ele 2m 
F9FT beam is only 3dB more than a 5-ele 6m YU7EF, and you can actually 
feed a bit more in at the bottom whilst still arriving at 400w at the 
top (even more so when you get to the higher bands, of course).

I'm not sure the argument that "people have a typical setup they will 
always use" stands: I'd imagine anyone for whom contesting is a major 
part of their operation will optimise their station for the rules of the 
contests they enter. If the rules change, so will the stations!

73,
Rob

On 30/01/2012 10:21, Rob Harrison wrote:
> Hi Rob,
>
> Ok you've picked a particular scenerio, one that's highly unlikely, 
> but you may have got your tongue stuck in your cheek :0)
>
> For starters who's going to go a buy a 600W amp, one expense, and two, 
> potential RFI problems if you decide to throw the halo in the bin for 
> a better antenna, as the halo compromises your RX capability. Plus if 
> you've got 3dB loss in the coax/connextors on 6M you are doing 
> something wrong or have a massive tower and extended feeder run, again 
> unlikely. Maybe a little more eduction is needed to show that antenna 
> gain works on RX as well as TX, making a beam much more attractive.
>
> Most entrants already have a set up they use for everyday use, a few 
> may modify that for a particular contest, but the majority will use 
> their day to day set up. That will most likely involve a beam of some 
> sort, why would you take that down to put up a halo? Granted if you 
> are portable, as you have no fixed set up, you can go with what you 
> want, but your scenerio is unlikely and if it did occur it would be in 
> very very small numbers.
> As you go up in frequency the scenerio gets even more unlikely, so a 
> good choice of band for your example.
>
> Your point is valid re the ethics of spraying your RF through 360, but 
> is that very much different to the current practice of multiple 
> antenna groups pointing in different directions, not necessarily in 
> UKAC though.
>
> 73
>
> Bob G8HGN
>
>
>
>
> ------ Original Message ----- From: "Robert Chipperfield" 
> <robert at syxis.co.uk>
> To: "Paul Selwood" <g3ydy at blueyonder.co.uk>
> Cc: <uk-contest at contesting.com>
> Sent: Sunday, January 29, 2012 10:16 PM
> Subject: Re: [UK-CONTEST] Power Limitations
>
>
>> Hi Paul (and others!),
>>
>> My concern - as I've mentioned before - is that ERP section limits
>> incentivise adding TX power rather than antenna gain. Of course this
>> doesn't apply to receive, so in that case let me present my
>> (potentially) winning strategy for 6m UKACs if we changed to ERP limits:
>>
>> Let's assume the "restricted" (AR) section was set at an EIRP of 500w.
>> That corresponds roughly to 100w at the TX (remembering the current
>> power rules for the restricted category /are/ at the transmitter, not
>> the antenna, 3dB of coax and connector loss, and a 5-ele beam having
>> gain 10dBi (source: YU7EF EF0605).
>>
>> In that case, my new station will be 600w out of an amp to a Halo (~2dBi
>> gain? Can't find a reference on that, tweak TX power accordingly...),
>> giving an EIRP of ~500w (remembering we now do take coax loss into
>> account, and the license limit of 400w applies at the antenna) on
>> transmit, and the old 5-ele beam on receive.
>>
>> My transmit performance is now identical to the current 100w section,
>> and so is my receive. But I do better, because my transmit power is
>> equal to its current maximum but in all directions simultaneously! How
>> cool is that! I can spin the beam 360 degrees within about 2 seconds
>> (armstrong rotation), which is probably quick enough to cover all
>> geographies of interest within the time it takes someone to say their
>> callsign, so I probably won't miss too many callers.
>>
>> Why is this a bad thing? Because now, rather than me consuming 3kHz of
>> spectrum in a relatively narrow beam, I do so in all directions, all the
>> time. Great for keeping my channel clear, but in my opinion not so great
>> ethically.
>>
>> We're already seeing very significant congestion during UKACs on the
>> more popular bands - encouraging setups such as the one above surely
>> isn't what we want to be doing?
>>
>> I don't think the above is too much of a contrived example - it uses
>> reasonable kit that most stations have available (except, perhaps, a
>> 600w linear, but they're not so rare), and reasonable numbers. If UKAC
>> AR become a 500w EIRP limit, I'm not sure why you wouldn't do it.
>>
>> Unless, of course, you kept the limit on single antenna working in AR.
>> At which point, I think, Bob would still be upset! :-)
>>
>> 73,
>> Rob, M0VFC
>>
>> On 29/01/2012 21:21, Paul Selwood wrote:
>>> Currently not having much time for amateur radio it is interesting 
>>> to review
>>> loads of emails on this reflector covering one subject in the space 
>>> of a few
>>> minutes, especially this one on changing the sections in VHF 
>>> contests in
>>> general or just UKAC to relate to ERP rather than purely Power. I 
>>> leave the
>>> point of measurement  vague on purpose as there had been discussion 
>>> as to
>>> where the power is measured at the antenna or at the transmitter 
>>> output. I
>>> stress that I believe that Bob (G8HGN) is only referring contests 
>>> for VHF
>>> and above.
>>>
>>> Bob  (G8HGN) has stated his case well with 100W to dipole and 100W to a
>>> large beam giving wildly different ERP being fired into the ether. 
>>> His point
>>> is that the sections in a contest should be set up around ERP, and not
>>> merely the transmitter power. It is up to the legislating authority to
>>> decide the sections and limits. They can also come up with guideline 
>>> figures
>>> for antenna gain thus leaving the vagaries of manufactures' 
>>> specifications
>>> out of it. Site cannot be taken into account either. Some contest 
>>> groups do
>>> rather well operating from non-elevated sites.
>>>
>>> Ray (G3HRH) raises some valid points regarding measurement gain of 
>>> antennas,
>>> this also applies to the measurement accuracy of RF Power. Even with 
>>> the
>>> Bird 43 attached to the end of feeder from a "Typical"  yagi will 
>>> only  a
>>> +/-10%   measurement uncertainty at best if  you are lucky.
>>>
>>> In these days when the catch phrase is a "level playing field" let's 
>>> ask the
>>> CC to consider this one. They did in the case of the M5 rule that has
>>> supposed to have levelled the field regarding geographical location. 
>>> Now
>>> let's go for it in the case of power fired into the ether e.g. ERP.
>>>
>>> Paul
>>> G3YDY
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> UK-Contest mailing list
>>> UK-Contest at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/uk-contest
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