[1000mp] cost of improved IMD performance

[Tom Rauch]

> A typical marine HF-SSB radio, FCC type-accepted and fully compliant
> with ITU and CEPT requirements, has a transmitter IP3 spec. of -32 dB
> relative to PEP at 150W PEP output. This radio is designed for a
> nominal 13.6V DC supply, and uses 13.8V PA devices.

Amateur rules are different, but in neither case is is legal to cause 
interference when it is the transmitters fault regardless of level.  

For marine use IP3 is not restricted. The technical standard is now -
35dB at any frequency removed from the assigned channel by more than 
150% and up to 250%, and at least -43dB plus 10log ten of MEAN power 
in watts dB beyond 250% of assigned channel width. 

If you were assigned 3800kHz, and had a 3kHz channel width on LSB,  
3rd order IM distortion from a pair of tones near 3kHz would have to 
be a minimum of -35dB. That is very easy and inexpensive to do.

The reason amateur radios are worse is because no one holds the 
manufacturers to any standard. We accept crappy performance like -
25dB IM3, and keyclicks 3kHz wide despite the fact the cost 
difference is nearly zero to build a clean rig. 
  
> Can we as radio amateurs really expect much better than this from the
> manufacturers, when we are a much smaller market segment than maritime
> users, and our price point is often significantly lower than theirs?

Yes, we should expect the same or better. It is very easy to meet 
that requirement. Collins made -50dB IP3 in transmitters in the 
1960's. 

As a cost example, my IC751A does much better than -35dB after 
changing the driver transistors to different types. As a matter of 
fact, with just that simple change it is 15dB better than stock form!

If I deduct the wholesale price of the original transistors from the 
replacements I used, ICOM would have saved $0.56 US per radio to make 
it cleaner. Contrary to popular misconception, it is NOT noticeably 
more expense to build a radio that does not click or splatter 
excessively.

It isn't a cost issue, the real problem is there is no representative 
working for amateurs who demands for any sort of minimum 
performance.73, Tom W8JI
W8JI@contesting.com