[TenTec] PROGRESS ON FIXING DIRTY TRANSMITTERS (SHERWOOD)

[rick@dj0ip.de]

Rob responded to me last night on this topic and I hope EVERYONE reads this
and finally understands that the time for addressing these issues (there are
several) is NOW!

See below:

73 - Rick, DJ0IP
(Nr. Frankfurt, Germany)


From: Rob Sherwood [mailto:rob at sherweng.com] 
Sent: Friday, December 11, 2015 7:18 AM
To: Rick - DJ0IP / NJ0IP
Subject: FW: Re: [TenTec] Dirty Transmitters - Flex and Yaesu

I tried to post the following, but it was rejected by the moderator since I
am not a member.
I will forward my other answer to your question, and if appropriate, maybe
you can post them for me.
Rob
NC0B

From: Rob Sherwood 
Sent: Thursday, December 10, 2015 1:42 PM
To: tentec at contesting.com
Subject: RE: Re: [TenTec] Dirty Transmitters - Flex and Yaesu



A plan to include transmitter cleanliness on my web site is overdue.  Just
recently I have added the capability of measuring transmitted phase noise. 
When incorrect data was published in QST on the new K3 synthesizer (or K3S),
it became necessary to be able to confirm or challenge these measurements
made by the League.  

The overall transmit bandwidth problem, however, is complex.  Only measuring
third-order transmit IMD for SSB is certainly not adequate, or even adding
5th order data. An important question is how fast the higher-order products
drop off.  For instance the FT-450 is 29 dB worse on 9th order than a
Collins 32S-3.  IMD varies by band and power level, and to some extent the
load presented by an antenna vs. a dummy load.

ALC overshoot can be a real splatter maker, and is often different on SSB
than CW.   I have seen modest CW overshoot where the SSB overshoot was
terrible, requiring recalls by Icom (IC-7410) and Kenwood (TS-590S). 

I find that testing SSB transmit bandwidth with 5-kHz band limited white
noise is really an eye opener.  That is a picture on a spectrum analyzer,
and not a number, unfortunately.  For instance, most transceivers today that
run on 13.8 volts are down 60 dB 5 to 7 kHz from the edge of their
transmitted passband (not the center of the passband).  That means the
average signal is 14+ kHz wide at -60 dB (6 kHz + 2.4 kHz + 6 kHz)  

On CW, key clicks are associated with rise and fall time, plus the shape of
the waveform if handled in DSP with modern radios.  One top OEM didn’t
realize that a 1.4 millisecond rise time was no good !  Stunning.    

Once a standard could be chosen for the exciter measurement, how do we get
the average amateur to monitor his linear with some kind of a peak-reading
device?  This can be an  ACCURATE  peak-reading watt meter or an
oscilloscope.   Personally I use a scope 100% of the time.  I have no idea
how I coped with not flat-topping my linear back in the 1970s.  Of course
there are many hams who don’t understand why their Bird watt meter doesn’t
read 100 watts on SSB when key down it reads 100 watts.  

73, 
Rob Sherwood
NC0B