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Re: [TenTec] ORION BCI

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] ORION BCI
From: Robert & Linda McGraw K4TAX <RMcGraw@Blomand.Net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 27 May 2005 20:57:15 -0500
List-post: <mailto:tentec@contesting.com>
Based on a report that inserting a 6 dB attenuation at the RX input and that 
reduced the BCI which was S9 + 20 dB or so tells me that the IM is being 
generated in the radio.  If it were external then it would have been reduced 
by 6 dB.

Keep in mind that IM does require 2 or more signals mixed in a non-linear 
environment.  Someone commented that a 2nd harmonic of a 50KW  AM  was the 
root cause.  That causes me to ask, where's the 2nd harmonic being 
generated?  It very well could be the junction of the ham radio tower and 
the guy attachment point.  Very common event.  Hence, guy wires should be 
bonded to the tower in high foreign RF environments.  Just wrapping a guy 
around a tower leg is not adequate.  If the IM changes in wind and or 
weather, you can bet on it being a bonding issue that needs attention.

If the 50KW BC signal then mixed with its own 2nd harmonic the sum of the 
two will be heard.  (BC freq + 2x BC freq)
Example:  650 kHz + 1300 kHz = 1950 kHz   (This is the fundamental plus the 
2nd harmonic summed)  This is WSM in Nashville, TN and not a fault of WSM 
but of the local environment at the ham station.  Another local example: 
1300 KHz + 1960 kHz + 650 kHz =  3910 kHz  (This is the 2nd harmonic of 650 
plus the 2nd harmonic of 980 plus the fundamental of 650)

Again a 50 KW of 1510 x 2 + 5KW of 980 = 4000 kHz  The modulation plays 
havoc with the 3980 TN net freq. in certain areas of Nashville.  The 
sidebands are 2x width for the 1510 fundamental.  Another factual example in 
Nashville TN.  Being WLAC AM 1510 and WSIX AM 980, again neither the fault 
of the BC stations.

In both examples the 2nd harmonic was being generated by the galvanic 
junction at the ham tower.  The two BC stations were clean so to speak.

Now, to validate the testing, if the IM is heard on one radio but not on 
another with the same antenna configuration and location, one might then 
presume that the IM is being generated in the radio of question.   If adding 
6 dB of external input attenuation kills the IM then for sure it is in the 
radio.  If the IM drops by only 6 dB then the IM is external.

73
Bob, K4TAX

----- Original Message ----- 
From: "Lee Crocker" <w9oy@yahoo.com>
To: <tentec@contesting.com>
Sent: Friday, May 27, 2005 3:26 PM
Subject: [TenTec] ORION BCI


> If the diodes are reverse biased, then it sounds to me
> like you lost bias.  Could be nothing more than a
> loose plug on the board.  Why do you presume the
> problem is a design flaw and not just a glitch in your
> radio?  If your TS-930 developed a cold joint that
> began acting as a diode would you then say Kenwood
> made a design error?
>
> 73  W9OY
>
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