help with SSB output

[1iwilly]

ok on my Cobra 2000 gtl i need help or guidance on how to balance the power output from channel 1 to 15 I'm seen close to 15 watts rms
the higher I go on freq power start to drop I've done these 2 mods but no change=
IC-5 tx-mixer change R190 from 100 to 47ohms then put a 330ohm from pin-5 and this one=ssb low power on IC3 balance modulator remove c207=47pf and change R206 from 270k to a 35k also when i try to balance the power output am starts to drop any tricks to balance it out like a happy medium thanks

 

[nomadradio]

Um, before we get too far, you are measuring wattage on a dummy load, right?

Because if these readings are from an antenna, the radio is not the only factor causing the power reading to change as frequency changes. Using an antenna just puts a wild card in the deck. A dummy load has the exact same impedance across the channels. An antenna does not.

Making sure that L44, L45, L46, L47 and L48 are all peaked on channel 20 helps. To make the slug's peak sharper, we choose one sideband, feed a tone into the mike, and turn the mike gain down for a power level of under 3 Watts. Peaking slugs with the power level too high flattens out the peak.

Once this is done, have a close look at the slug in each of those cans. Every one of them should show a peak with the body of the slug at least two turns below the rim of the hole in the top of the can. If any of them are DEAD FLUSH with the rim of the hole, this will skew the radio's transmit bandwidth until it's fixed.

This is our standard procedure. Your mileage may vary.

73

 

[1iwilly]

Um, before we get too far, you are measuring wattage on a dummy load, right?

Because if these readings are from an antenna, the radio is not the only factor causing the power reading to change as frequency changes. Using an antenna just puts a wild card in the deck. A dummy load has the exact same impedance across the channels. An antenna does not.

Making sure that L44, L45, L46, L47 and L48 are all peaked on channel 20 helps. To make the slug's peak sharper, we choose one sideband, feed a tone into the mike, and turn the mike gain down for a power level of under 3 Watts. Peaking slugs with the power level too high flattens out the peak.

Once this is done, have a close look at the slug in each of those cans. Every one of them should show a peak with the body of the slug at least two turns below the rim of the hole in the top of the can. If any of them are DEAD FLUSH with the rim of the hole, this will skew the radio's transmit bandwidth until it's fixed.

This is our standard procedure. Your mileage may vary.

73

does it matter on the sequence i usually start on 48,47,46,45, then L38

 

[Beetle]

does it matter on the sequence i usually start on 48,47,46,45, then L38

It matters in that your antenna is an unknown quantity in the mixture. Get a good, reliable 50 ohm dummy load that'll handle the power.

 

[loosecannon]

1iwilly,

you can use L46 and L45 to balance the power between channels 1 and 40.
it takes a bit of trial and error but you should be able to get it even across the 40 channels and more if the radio has them.
also, as others have said, only a known good dummy load should be used.

you can also up the value of C163 to 5pF (some chassis already have this value there so check first) to wideband the TX a bit.
LC

 

[DTB Radio]

1iwilly,

you can use L46 and L45 to balance the power between channels 1 and 40.
it takes a bit of trial and error but you should be able to get it even across the 40 channels and more if the radio has them.
also, as others have said, only a known good dummy load should be used.

you can also up the value of C163 to 5pF (some chassis already have this value there so check first) to wideband the TX a bit.
LC

One other broad-banding trick is to put a 200-ohm resistor across pins 11 and 13 of the SO-42P TX mixer IC. I think those are the correct pins, I'm not at the shop to check my notes. I know its two pins near the connection for L47.