On Apr 4, 2006, at 9:48 AM, Gary Schafer wrote:
>
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com
>> [mailto:amps-bounces@contesting.com] On
>> Behalf Of Ian White GM3SEK
>
>
>> By changing to the common US convention of "dB below PEP", that figure
>> instantly "improves" to -36dB :-)
>
> I wish all would stay with your convention (the proper way) of dB
> below a
> single tone of two tones when expressing IMD. :>)
There are two ways of measuring IMD, and neither one is "proper". The
Ham method is relative to PEP, which is more meaningful because it is
what one sees - relatively speaking - on the air with an S-meter.
>
> After all, even if you note that the IMD figure is below PEP, it is
> still
> incorrect because only one product (1/2) of the IMD is being related
> to PEP.
An S-meter sees all of the IMD products when the Rx is tuned c. 4kHz
from a SSB signal.
>
> PEP is the result of the sum of two tones or carriers.
> If for example 3rd order IMD is to be referenced to PEP it should
> include
> the sum of both 3rd order products, the sum and difference products
> and not
> just one of those as is commonly done. That would give the same
> difference
> as the proper way "dB below a single tone of two tones".
>
> Bill Orr states this in his handbook.
Bill Orr was the originator of the idea that putting an RF choke from
the grid to ground of a 3-500Z would create desirable RF-NFB. Do you
agree, Gary?
>73
> Gary K4FMX
>
>
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>
>
Rich Measures, 805.386.3734, AG6K, www.somis.org
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