>> Does a transmitter with poor 3rd order IMD therefore have any noticeable
>> distortion in the voice quality due to the speech intermod products within
>> the audio bandwidth?
>
>Why would it have audible distortion? The garbage being measured is already
>20-30dB down, is outside the passband of the receiver fileters, and the
>receive detector and audio system already has IM products. Not only that,
>many locations have high noise levels masking IMD that can be heard in quiet
>locations.
Looking at the ARRL graphs of transceiver IMD testing, and comparing
different rigs by their 3rd order products, if one rig has poor 3rd IMD
results it does not necessarily follow (according to the graphs) that the
higher order products are also going to be worse. For example, for the 160
meter result at -4 KHz, the TS2000 has a spur at -55 dB, and the FT1000MP
is at -50 dB. Both rigs are below 60 dB at 10 KHz. So, if the 3rd order
distortion is not audible (not that I thought it would be;) and its value
does not indicate the amount of the higher order IMD, then what is the
purpose of having the 3rd order IMD specification?
>There is also a BIG difference between off-frequency products and distortion
>that you can hear inside the passband. The same is true for keyclicks. What
>you hear inside the passband is not related to actual bandwidth.
That I understand, what I don't understand is how one rig is deemed to be
"better" than another relative to transmitter IMD, when graphs show that
each has its advantage but on different bands.
>If you look at measured performance, price has little to do with results.
Of course, I didn't mean to imply otherwise.
>Look at close-spaced receiver tests at:
>
>http://www.w8ji.com/receiver_tests.htm
I really enjoy visiting your website, it has a lot of very good and
interesting stuff.
>The cheap (old technology) K2 receiver which isn't especially well-designed
>equals or beats all of the receivers on that page.
Well, going back to the track of transmitter/amplifier IMD, the ARRL tests
show that the K2 does have better 3rd order transmitter IMD performance
than the TS2000 on all bands except for 10 meters. However looking at the
5th order case, the TS2000 beats the K2 on all bands except 80 meters. So
in terms of IMD, which is the better radio transmitter?
--
Zyg AF4MP
Roswell GA USA
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