[Amps] How to read the 3-500Z spec sheet?

[Carl]

If the average ham simply reduced the power of his ricebox to 75-80% of its 
ratings he would pick up a 3-6dB IMD improvement at least. Then he can use a 
decent amp instead of operating in GIGO mode.

Carl
KM1H


----- Original Message ----- 
From: "Joe Subich, W4TV" <lists at subich.com>
To: <amps at contesting.com>
Sent: Sunday, May 23, 2010 4:10 PM
Subject: Re: [Amps] How to read the 3-500Z spec sheet?


>
>> For the average ham, it's far better to measure PO1dB (1 dB output
>> power compression level) and always operate linear modes below that
>> point. That guarantees the best compromise between power out and
>> linearity on any amplifier with minimal test equipment and
>> experience.
>
> The average ham has even less ability to accurately measure the
> 1 dB compression point on an amplifier than he has of accurately
> measuring IMD.  Most don't have one accurate wattmeters much less
> two ... nor the ability to understand the issues of exciter foldback
> and the changes in SWR between the exciter and amplifier with tuning.
>
> 73,
>
>    ... Joe, W4TV
>
> On 5/23/2010 3:49 PM, Larry wrote:
>> Well Jeff,
>>
>> I both agree and disagree with your statements below. I agree with
>> your statement about guys not measuring at all. But I strongly
>> disagree with telling these same guys they can do "adequate"
>> measurements with an incorrect setup.
>>
>> The guys you are targeting are not competent enough to discern the
>> difference between sound card setup issues, exciter issues, and
>> amplifier issues. The average guy needs to have an idea what is
>> required to do real testing of an amplifier BEFORE you give him the
>> easy way out. And you need to detail the "easy" setup including the
>> tests at each stage.
>>
>> I strongly disagree with proliferating half ass measures which will
>> invariably produce even more junk science than we are already dealing
>> with.
>>
>> For the average ham, it's far better to measure PO1dB (1 dB output
>> power compression level) and always operate linear modes below that
>> point. That guarantees the best compromise between power out and
>> linearity on any amplifier with minimal test equipment and
>> experience.
>>
>> 73,
>>
>> Larry - W7IUV DN07dg - central WA http://w7iuv.com
>>
>>
>> On 23-May-10 12:11 PM, Jeff Blaine AC0C wrote:
>>> Larry,
>>>
>>> You are 100% right if an absolute accurate measurement is needed.
>>> But if you simply want to know if you are in the 20's or the 30's,
>>> then the method I describe is fully adequate to the task.
>>>
>>> I just completed protos of a crystal modified Wentzel design with
>>> some tweaks added by Bill Carver that is for high DR3 range
>>> receiver testing. We are talking about IMD levels for the entire
>>> system of sub -110dbc. Right on all counts - LPFs needed - ferrites
>>> needed - lots of added return loss via pads sprinkled. I'm fully on
>>> board your claim here. But just not for Joe's basic ham shack
>>> needs. For the basic "is my tx/amp combo generating crap" kind of
>>> test, the 10dbc better rule of thumb for the sources is good enough
>>> and the modern sound card without being overdriven is fully up to
>>> the task.
>>>
>>> The problem as I view it is that guys are not measuring at all. Or
>>> if they are it's with something like an SB610 or whatever. To my
>>> thinking, better to have some minimal indication even if it's
>>> "gross" in resolution than none at all. This solution provides that
>>> - it's better than the SB610 at least. And given the number of
>>> "I've never built anything before and don't really know what I'm
>>> doing" guys comments we see on the boards, this has got to be a
>>> step in the right direction. Even if it's filled with significant
>>> shortcomings.
>>>
>>> 73/jeff/ac0c
>>>
>>>
>>> -------------------------------------------------- From:
>>> "Larry"<larry at w7iuv.com> Sent: Sunday, May 23, 2010 1:51 PM To:
>>> "Jeff Blaine AC0C"<keepwalking188 at yahoo.com>; "AMPS"
>>> <amps at contesting.com> Subject: Re: [Amps] How to read the 3-500Z
>>> spec sheet?
>>>
>>>>
>>>> On 23-May-10 10:45 AM, Jeff Blaine AC0C wrote:
>>>>>
>>>>> Of course, a real IMD test requires a 2 -tone source and you
>>>>> can download those applications on the web free of charge.
>>>>
>>>> Wrong answer for amplifier testing. While you can approximate
>>>> proper "two-tone" testing with a sound card tone source when
>>>> evaluating a transceiver, a LOT more is required for accurate and
>>>> technically correct amplifier testing.
>>>>
>>>> To do accurate IMD (and more correctly OIP3) testing on an amp,
>>>> you NEED two separate clean signal sources. This means two
>>>> exciters that are known to be very clean and free from harmonics
>>>> (much greater than 60 dB down) plus a high power combiner and
>>>> usually a set of bandpass filters at each of the tone
>>>> frequencies. Plus, just to keep everything happy, a bunch of
>>>> attenuators sprinkled around the bench.
>>>>
>>>> Anything less and you are only testing the source(s) and not the
>>>> amp. Some time back, W8JI detail the correct test setup for
>>>> amplifier testing and I think it's on his web site someplace.
>>>> Anything less and you are just fooling your self.
>>>>
>>>> 73,
>>>>
>>>> Larry - W7IUV DN07dg - central WA http://w7iuv.com
>>>>
>>>>
>>>
>>>
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