Pillbox Presenting Significant SWR

[Wire Weasel]

Hi guys, First time experiencing this problem. Antenna, coax and radio all known good. Straight hookup SWR on Imax 2000 is 1:2 - I've recently been using a a little 2 pill Pride 100 and it showed no additional SWR.

Just picked up a Boomer 400 Deluxe 4 pill. Seems to all work fine. Shows a good 250W p.e.p. as should for the 4 x mrf455's in it. Once you get above …. say a 25w dead key out the SWR climbs to 2.5 and will go higher with increased carrier. SWR swings backwards with modulation. ~ From what I've read and heard this is an impedance mismatch in one of the chokes. It is a significant enough mismatch that it is causing SSB modulation to be unclear/muffled …. even with the amp turned off …. and also shows a corresponding 30% reduction in output power from the radio. Remove amp from circuit and SSB modulation is very good - normal and radio operates as should. Is a Galaxy 99V2. Radio on max power is set right at 10 watts. Connected through amp it gets cut back to 7 watts. - I have numerous jumpers around in differing lengths and have tried everything from 2 feet to 10 feet. Usually use a typical 3 foot mini 8 jumper. No other jumper or combination of jumpers made much of any difference.

I can obtain an antenna tuner to run between the radio and amp (don't have one at present) but if there's an easy fix to try inside the amp I'd rather try that first. I've heard you can experiment with adding more wire loops to one of the coil-chokes. I have no idea which one(s) are in question.

Can anyone point out which of these chokes I need to experiment with? Looking around I see nothing burned or out of place. Thanks in advance for any help !!!

 

[Crusher]

What kind of power is the 99v2 doing? That palomar is best for a single final radio. Those455's don't need much drive

 

[vkrules]

What kind of power is the 99v2 doing? That palomar is best for a single final radio. Those455's don't need much drive

Hi guys, First time experiencing this problem. Antenna, coax and radio all known good. Straight hookup SWR on Imax 2000 is 1:2 - I've recently been using a a little 2 pill Pride 100 and it showed no additional SWR.

Just picked up a Boomer 400 Deluxe 4 pill. Seems to all work fine. Shows a good 250W p.e.p. as should for the 4 x mrf455's in it. Once you get above …. say a 25w dead key out the SWR climbs to 2.5 and will go higher with increased carrier. SWR swings backwards with modulation. ~ From what I've read and heard this is an impedance mismatch in one of the chokes. It is a significant enough mismatch that it is causing SSB modulation to be unclear/muffled …. even with the amp turned off …. and also shows a corresponding 30% reduction in output power from the radio. Remove amp from circuit and SSB modulation is very good - normal and radio operates as should. Is a Galaxy 99V2. Radio on max power is set right at 10 watts. Connected through amp it gets cut back to 7 watts. - I have numerous jumpers around in differing lengths and have tried everything from 2 feet to 10 feet. Usually use a typical 3 foot mini 8 jumper. No other jumper or combination of jumpers made much of any difference.

I can obtain an antenna tuner to run between the radio and amp (don't have one at present) but if there's an easy fix to try inside the amp I'd rather try that first. I've heard you can experiment with adding more wire loops to one of the coil-chokes. I have no idea which one(s) are in questio
Can anyone point out which of these chokes I need to experiment with? Looking around I see nothing burned or out of place. Thanks in advance for any help !!!

Your describing classic overdrive . Not unbalanced spliter / combiners.
25watts dead key is way to much drive for 4x 455s your just overdriving it.The high SWR is due to spurious emissions on frequencies other than 27 mhzs(outside the swr range of your ant) Try about 8 watts dead key and 20 watts SSB P.E.P . The loss with the amp in line and bypassed is a little high but not uncommon with cb amps. Turn down the drive and enjoy.

 

[vkrules]

The loss might not be as high as you think try it on a dummy load not a antenna.

 

[tba02]

I'd drop it way down on AM and see how it behaves. I'd also start around 12 watts for SSB and work up from there until gain

3 watts Pin ~ 70 Pout @ 13.6 v (30 mhz).
1.5 watts Pin ~ 60 Pout @ 13.6 v (30 mhz).
http://cdn.macom.com/datasheets/MRF455.pdf
Look at figure 3 for 1.75 watts.

 

[vkrules]

3 watts Pin ~ 70 Pout @ 13.6 v (30 mhz).
1.5 watts Pin ~ 60 Pout @ 13.6 v (30 mhz).
http://cdn.macom.com/datasheets/MRF455.pdf
Look at figure 3 for 1.75 watts.[/QUOTE]
per pill it's a 4 pill amp
looking at the curve 1 watt per pill would be optimum.

 

[Wire Weasel]

The 25 watt dead key was out of the amp, not the radio. The 99V2 is a medium power export and will only do 10 watts max dead key. To get the 25 watt dead key out of the amp was only about 2.5 watts out of the radio.

 

[Crusher]

I don't see any feedback networks on that amp. I would start there. Could be having an oscillation issue. Might clean up a little.

 

[grimace]

does the output tuning capacitor have crack on it are does it just look like it does

 

[Wire Weasel]

Is that the single larger cap in the very back - middle?

 

[Crusher]

Yup, that does look cracked or split

 

[Wire Weasel]

No, it looks all good. I can test it though with a capacitance meter.

 

[Wire Weasel]

I believe this is going to be a situation similar to one being discussed in another thread …. that the factory did not tune the input properly to 50 ohms. I can add wire to one of the chokes …. just need to be sure which one to modify. Is it the one I have circled? Need to know for sure please …. no guesses ;-)

 

[Wire Weasel]

I've ordered some heavy duty 5amp axial 10uh chokes from Mouser. Will stick one on the input and let y'all know how it goes