>
>
>-----Original Message-----
>From: Tom Rauch <w8ji@akorn.net>
>To: amps <amps@contesting.com>; Steve Thompson <g8gsq@qsl.net>
To: <amps@contesting.com>
>Date: 20 February 2002 01:07
>Subject: Re: [AMPS] Power out indicator
>
>
>>
>>
>>>> much lower working Q and so offer higher efficiency.
>>
>>>I'm wide open to
>>> correction here, but I think If you are matching between two
>>> resitances, the L match has the lowest loaded Q. To get lower, you
>>> have to cascade L matches.
>>
>>Looking at a typical inductor Q=300 and capacitor Q=5000
>>matching 50 ohms to 1000 ohms with 1500 watts on 1.83 MHz:
>>
>>L network Qeff=4.36 C=380pF L=18.96uH and loss = 25.7watts
>>T network Qeff=4.7 C=389(2) L=19.45uH and loss=24.5w
>>Pi Qeff=4.7 C=389(2) L=19.45 and loss=24.5w
>>
>>While the effective operating Q is slightly higher in the T and Pi,
>>loss is lower.
>I agree there's little doubt that the L network rarely has a significant
>advantage compared with the tuning flexibility of the others.
? Advantages of the L-netork are:
1. lowest circulating current through the inductance -- i. e., the
reactance with the most potential for power loss.
2. ideally suited for balanced transmission lines (the balanced L).
3. two controls instead of three or four, so no inappropriate settings
of the inductance is possible.
4. configuration with greatest power handling ability.
5. no ferrite core balun to saturate with typical SWRs on bal.
transmission lines.
? Disadvantages of the L-network are:
1. Unavailable to appliance operators. [sad violin music in background]
2. Requires a SPST switch to match <50? loads. (however, experience
shows that including the low-Z switch in your design virtually guarantees
in writing that a <50? Z will not exist in any Ham-band on your
ladder-line-fed multiband antenna system)
>Correcting a
>previous comment of mine, where there are reactive components to be matched,
>pi/T can have lower loaded Q than L.
>
amen, Steve
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
end
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