[SEDXC] Spectrogram Resource & FT-2000 Test Update

[Don Nesbitt]

I've had a number of requests for more information on the Spectrogram 
software program that I used to show filter characteristics and do my "quick 
and dirty MDS" test on John's rig during the "Merry-Go-Round Radios" 
presentation at our last meeting.

The last "free" version of Spectrogram (version 5.1.7) can be downloaded 
from Tom Hammond's (N0SS) site at:  http://www.n0ss.net/index_k2.html  You 
can also find it on a number of other sites - a google search will show you 
some alternatives.  While limited, the free version will do everything that 
I demonstrated at the meeting and more.

On Tom's site, the download is a little more than half way down the page.  
While Tom's application is primarily directed toward setting up the filters 
on the Elecraft K2, his general discussion is appropriate for use with most 
any rig.

The latest "paid for" version of Spectrogram costs $49.95 and has lots of 
additional functionality.  You can find it at:  
http://www.visualizationsoftware.com/gram.html

When using Spectrogram please keep in mind that it is audio and its 
usefullness is limited by the dynamic range of your sound card as well as 
the noise floor of your computer.  In general, do not exceed about -30 db at 
the top of your trace for most computers.

Also be aware that there may be various shaping circuits in the audio 
section of the receiver under test (transceiver in our demo).  For those of 
you who were at the meeting, you may recall that the SSB filters in John's 
rig showed a rather pronounced downward slope instead of a nice flat plateau 
that was seen on the K2.  I'm guessing that it was because there was some 
audio filtering in the headphone line which is where the audio was being 
taken off.  If the "external speaker" jack on the rear of the radio had been 
used (I should have done that!), I suspect the filter shape would have 
looked much different!

By the same token, it is fun to examine the effects of various shaping 
options in the rig as well as IF shift, notch and peaking functions, etc.  
Have fun with it.

Bottom line is to try to get as close to an "unshaped" output as possible 
and keep the trace relatively low if you simply want a quick look at the 
filters.

FT-2000 Check Ride

Those of you who were at the meeting saw the rather dramatic difference 
between the close in 2 kHz 3rd Order Intercept Point in the FT-2000 when 
compared to the FTDX-9000, Icom IC-7800, and TenTec Orion II.  For the 
FT-2000, the point was more than 40 dbm down from the IC-7800 and the Orion 
II.  That's a pretty miserable number!

It is important to keep in mind that the 3rd Order Intercept Point is 
generally NOT a "measured" number.  It is extrapolated based on other 
measurements.  A number of years ago, Lloyd Butler (VK5BR) wrote a nice 
explanation of Intermodulation that included a simple explanation of the 3rd 
Order Intercept Point.  It is worth reading (of course there are many other 
sources that present great information - again - google it - you will find 
Tom's site as well - www.w8ji.com).  Lloyd's piece can be found at:

http://users.tpg.com.au/ldbutler/Intermodulation.htm

The question is - does this make any difference in actual practice - on the 
air - in the "real" world, etc?

Tad (WF4W) did a great job in his comparison of his FT-2000 to his FT-1000MP 
Mark V.  Now the really great part is that he "rented" his FT-2000 to me for 
a week while he was away on business.  This time, the price was right - 
free!  I spent an average of 7 hours a day for 6 days, ABCDing the FT-2000 
with my Orion II, modified and INRADed Mark V, and K2  under lots of 
conditions including about 8 hours in the SSB DX contest.  Now, your mileage 
may vary but I have to say that in spite of the dismal 3rd Order Intercept 
Point numbers posted by the FT-2000, I really can't say that it caused the 
radio to perform badly.  In my "real world" of poor antennas and high noise, 
it was a non issue.  In spite of some rock crushing signals in the DX 
contest, I didn't notice any artifacts being generated in the radio that 
were not just the usual "crud in the passband" from 40 over nine signals 
close by.  The same crud was there in the Orion II, the K2 and the Mark V.  
In your environment it might be different but hey - if your radio isn't 
generating it in the rf and mixer stages, and the other guy (or gal) is 
putting crud in your passband, it's in your passband!

Of course being the curmudgeon that I am, I will have to say that while that 
radio certainly has knob power, they are pretty small and awfully close 
together.  Electronically, its got some really nice features - like the 
variable contour control - this is excellent!

Check with Tad to see when he is going out of town again ;-)

73 es gud dxing -- Don N4HH

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