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X-Force 600HD Smoked
- Thread starter Shadetree Mechanic
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- x-force
I found a panel mount 464 and took the bracket off. Put it in and the SWR on the input is the same 3:1 at any adjustment. So then I put the 330pf caps back on the transformers. Then I could adjust from 3:1 to 2:1 but that's the lowest it will go. I will get some trimmers to put across the input transformers so I can dial it in. The 955 would do ok with 2:1 but it would bug me not to get it below 2:1. Stay tuned.
I happen to have a pair of 468 and 300pf is in the middle of the range. I put some paper clip legs on them to get them away from the sand bars.
I wonder if I need more turns on the input transformers? Fewer turns? Maybe the transformer ferrite is the wrong mix? I will test it again after supper.
Half the trick with licking this issue is knowing the direction of the error. Is the input twice the desired impedance? Or half?
Two to one SWR only tells you the magnitude of the error, not the direction up or down from 50 ohms.
Quick and dirty way is to take a 100 ohm resistor a couple of Watts rating or more, and shunt it in parallel with the amp's input. From the center of the input-side coax coming from the relay to ground.
If this pushes the reading above 2 to 1, the amp's input impedance is already below 50 ohms.
And if you see the reading fall, the amp's input is above 50.
A small coil between the input coax and the trimmer cap usually works best to bring down a too-low impedance. Placing the coil between the trimmer cap and the splitter input should help if it's too high. The tricky part is "how small" the coil needs to be.
Cut and try.
73
Two to one SWR only tells you the magnitude of the error, not the direction up or down from 50 ohms.
Quick and dirty way is to take a 100 ohm resistor a couple of Watts rating or more, and shunt it in parallel with the amp's input. From the center of the input-side coax coming from the relay to ground.
If this pushes the reading above 2 to 1, the amp's input impedance is already below 50 ohms.
And if you see the reading fall, the amp's input is above 50.
A small coil between the input coax and the trimmer cap usually works best to bring down a too-low impedance. Placing the coil between the trimmer cap and the splitter input should help if it's too high. The tricky part is "how small" the coil needs to be.
Cut and try.
73
Just out of curiosity, did you try tuning input with no capacitor across input transformers? Worth a shot!
I thought about it, but no I did not try that. With the trimmers, I was able to get to a point where the SWR did not make any further improvements as I went lower with the adjustments.
I put the 330pf caps back on the transformers and made a resistor up with a clip so I could A/B test it. With it connected, it would bring the SWR back up to 3:1. So reducing the impedance had a negative effect like it was already too low. So now I will work on making a small coil to go between the coax and input. Thanks for this bit of information, it took me a few times reading it before it sunk in.
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