[Central-Electronics] 100V sweep results

[Jim Candela]

----- Original Message ----- 
From: "K6JEK" <k6jek at comcast.net>
To: <central-electronics at mailman.qth.net>
Sent: Thursday, March 13, 2008 11:52 AM
Subject: [Central-Electronics] 100V sweep results
>Thanks for the various suggestions
>
> Jon
>

Reply by Jim, WD5JKO

Jon,

   This must be Phasing SSB carrier/sideband suppression week. Yesterday 
that was the topic on the every Wednesday 3870 at 7:30 PM Central time 'Boat 
Anchor' net with Lynn K5LYN as net control.
We had two Central Electronics 20A's in there, and another guy with a Heath 
SB-10 and a Heath Apache amplifier. It was interesting that the SB-10 guy 
had the best side band suppression. Lynn with his 20a + 600L was 10 db over 
S9 LSB at my QTH (Icom R75 receiver, ATTENUATOR on), and he was S3 when I 
switched to USB. If I assume 6db / S unit, then we have 6X6+10 or 46 db 
unwanted sideband suppression. The SB10 guy had no detectable unwanted 
sideband or carrier. He had just went through the alignment procedure 
though, so I doubt if the adjustments will be that tight for long.

   My report was not quantified well but my unwanted sideband was heard with 
my QRO 20A #2. This 20A runs about 60 watts PEP out on 80M, and makes a good 
exciter for my 8877 equipped G-G linear amplifier using a Dentron MLA-2500 
shell. On SSB I can hit 1500w PEP output without too much trouble with this 
setup. I decided after the net to go over my 20A tuning and see what I could 
do. I decided to optimize SB1 which for 80M is LSB. To make SB1 and SB2 the 
same usually results in a compromise. I changed the phase shifter module 
schematic a few years ago to extend the frequency range upward to 4 Khz 
because the 20A does not have a low pass filter like a 100V. I was able to 
get about 50 db sideband rejection from 1.5 Khz to 4 Khz, but that number 
degrades to about 30 db below 1 Khz. I figured this a workable compromise. 
So lets say I'm on LSB at 1 KW PEP, and then my unwanted sideband will be 1 
watt PEP below 1 Khz audio, and 10mw between 1.5 Khz and 4 Khz audio. I can 
live with that.

  I did use the scope method with a Wavetek function generator from the late 
1960's. The part that helped the most was to use external trigger on the 
scope from the audio source.

Maybe some of you in the group will join in next week, Wednesday, 7:30 PM, 
Central, 3870 Khz for the weekly 'Boat anchor net?

Regards,
Jim
WD5JKO