Front panel is on. RF PA is installed. Balanced Modulator problem fixed (?) Rig is on the air with about 3 watts, working lots of DX.
But there is an annoying amount of carrier that is still getting through. It is only about .5 watts with sidebands of 100 watts PEP, but it annoys me, and it makes the setting of the carrier frequency in relation to the filter passband very critical: If I set the carrier a bit too far from the passband I get improved carrier rejection (from the filter), but I also lose the lows in both received and transmitted signals -- the RX just doesn't sound as good. I see it in both of the 15-10 rigs (IF of 25 MHz). There is less of it in the 17-12 meter rig (IF of 21.4 MHZ), and none of it in the Mythbuster (75-20 meters) (IF of 5.2 MHz). I am now wondering if this might be a consequence of my using a very high (25 MHz) single conversion IF in the 15-10 rigs. What do you folks think?
From my log:
March 7, 2024 PUT VERSION 2 of the 15-10 RIG ON THE AIR!
10S 1528 OK2RZ Jiri – said I was 57!
15S 1539 S52WW 58 Damian.
15S 1602 SP1NQH Stev said I am big signal!
10S S58N 1726Z
10S S58N 1726Z
10S S57S 1728Z
10S IK4GRO Lauro 1735Z
10S W0CJV 1825Z Ft. Collins Gary
10s 2000Zish KK7TV Gary in Randy. Asked what software/microcontroller I was using.
10S KJ5MFF 2015Zish a middle school in New Mexico. KI5MFF control op sent picture
Posts
I think you are on the right track about the high IF frequency. Carrier suppression from the balanced mixers and whatever carrier supression the xtal filter can yield gets tougher the higher you go. That said, 23dB isn't a bad start. I'm sure it can be improved, even with the high IF.
ReplyDeletePunch List:
1) How well matched the diodes are? Are they 1N4148's or RF Schottky's? Or Minicircuits ADE?
2) What does the LO spectrum look like?
DBM's like sine or a true square wave.
Not with even harmonics in the LO spectrum.
3) How much rejection from the XTAL filter?
This comment has been removed by the author.
ReplyDelete