Comment from Rob Sherwood.
I completely agree with Tom on the issue of PIN diodes mods doing nothing.
In reference to the three different 781s on my web page, the numbers
show normal sample variation scatter.
The one with the PIN diode mod is 1 dB less than one sample and 6 dB
worse than the other.
I think we are looking at sample variation, and the PIN diode mod likely
has no effect, for better or worse.
The PIN diode mod could actually be worse, but I cannot prove that since
the tests were on three separate units.
A ham who is now SK did the mods on many 781s.
When I asked him how he tested the claimed dynamic range improvement, he
described how he measured the dynamic range using one generator.
Since it is impossible to measure dynamic range with one generator, one
can see how meaningless his measurements were.
I am also amused at how some hams with the new 7800 claim they can hear
so much more than with their old rig.
My 7800 can hear no better than my 75S-3C on 20, 17 or 15 meters on weak
DX.
Likewise some hams claim the Pro III is so much quieter than the Pro II.
My web site shows the two so close together, one could not possibly
notice the difference.
I guess at times we hear what we want to hear.
Tom W8JI wrote:
>>It's the same as swapping switching diodes in transceivers
>>to pin-diodes
>>without checking/correcting their current.
>>Thousands did.
>>Every day another fool awakes, one just hast to find
>>him...
>>
>>
>
>You know Peter, that is a good example of voodoo
>pathological science.
>
>I spent quite a bit of time investigating PIN diodes vs.
>regular diodes in my rigs and found absolutely no difference
>at all. Yet people who do the mods will swear they work.
>
>Look at Sherwood Engineering's site at a PIN modified ICOM
>781. Click here and find the "Sherwood's tests" link at the
>page top:
>http://www.w8ji.com/receivers.htm
>
>The modified 781 is 6dB worse for close spaced IM3.
>
>The best any of my tests did on a couple FT1000's was break
>even, yet people swear it makes a huge difference.
>
>Amplifiers are no different.
>
>73 Tom
>
>
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