You may wanna do about 5-6 turns on a 3/8” form. Then just use the piece of unshielded coax and start about the 4th turn and solder to. See what you get. May or may not need to move trimmer to other end of coil.
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X-Force 600HD Smoked
- Thread starter Shadetree Mechanic
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I stripped out some 12 awg Romex and made a 6 turn 3/8 coil. The swr is the same except instead of 1/4 turn from snug, the cap wants to be full snug. Like it needs a little more capacitance. I am going to swap a 468 back in the same spot.
You got something weird going on. It’s not this complicated. I’ve never had a problem like this.
Why is the black wire going out past resistors? What is that ceramic cap right by trimmer? It should tune easily. Why is that alligator clip on there? I’ve helped all I can. Without having it right in front of me. I can’t help you anymore
Why is the black wire going out past resistors? What is that ceramic cap right by trimmer? It should tune easily. Why is that alligator clip on there? I’ve helped all I can. Without having it right in front of me. I can’t help you anymore
There's something I've been wondering and may have missed. Are you using a dummy load and what radio are you driving it with? Try a Cobra 29/25 to eliminate the possibility of this being an exciter problem. A scope would be nice. If the thing is still oscillating that would explain the difficulty you're having.
The black wire is the bias power and the ceramic cap is part of the bias network. The alligator clip is a quick way to reduce the number of coils for testing purposes. Thanks for all your help. I really do appreciate it. Maybe the goofy bias arrangement is throwing me for a loop.
I am driving it with a Stryker 955 with the dead key set to 4 watts. I have a 29 that I can try too. The output SWR is 1:1 and doesn't even move the needle when modulating. This is into my antenna, I have not tried the dummy load yet. The input SWR used to be better before I changed the pills. I do have a scope but I assumed that it was not oscillating after I was able to get the output SWR down. I will have to check it to be sure.
Try using the 29 to get input tune right. Most of the 955’s I’ve seen on a scope and a spectrum analyzer are ugly.
I figured you weren't so much struggling with a huge problem, but enjoying working on it and discussing. At least I've enjoyed the great photos and all the input from everyone.
I suppose now you could always try Nomad's trick with the resistor again, with the coil now in place, to confirm you've not added so much to the impedance to be having the opposite problem.
You could also put another 464 at the other end of the coil and try tuning that way.
Anyone in the know...is it possible to "see" the input impedance with an analyzer? Or does it change too much when power is applied to provide anything useful?
EDIT, having gone back and read Nomad’s post he did seem to recommend the coil be placed between the cap and the combiner....and references the difficulty of making the coil “small” enough, which I’m assuming refers to the value and not physical size. If you’re having to add capacitance, maybe the coil is just too much, and/or maybe the cap would be better of moved?
I suppose now you could always try Nomad's trick with the resistor again, with the coil now in place, to confirm you've not added so much to the impedance to be having the opposite problem.
You could also put another 464 at the other end of the coil and try tuning that way.
Anyone in the know...is it possible to "see" the input impedance with an analyzer? Or does it change too much when power is applied to provide anything useful?
EDIT, having gone back and read Nomad’s post he did seem to recommend the coil be placed between the cap and the combiner....and references the difficulty of making the coil “small” enough, which I’m assuming refers to the value and not physical size. If you’re having to add capacitance, maybe the coil is just too much, and/or maybe the cap would be better of moved?
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Somehow I am making this harder than it needs to be. I appreciate everyone that has offered advise and everyone who is following along. I can hear the skip rolling when I go to test this thing. I just gotta make this work. I was going to make a new coil with about 3 turns, then I thought what the heck. I will try another trimmer on the other end of the coil just to see. So I grabbed the 464 and backed it off half a turn from snug and put it in.
Then wouldn't you know, the input SWR was 1.2:1 wow!
Man, that's great.
You probably just needed to spread the coil. No CB equipment really gets out until you do. If you have any other crunched up coils...you now know the drill to remove the bottleneck and stop holding back the powa'!
On a more serious note, I'm very happy to hear of your success! Hope it works out great for you.
You probably just needed to spread the coil. No CB equipment really gets out until you do. If you have any other crunched up coils...you now know the drill to remove the bottleneck and stop holding back the powa'!
On a more serious note, I'm very happy to hear of your success! Hope it works out great for you.
You might be able to jump a turn and get it flat on input. Just a thought
That input circus might accidentally be a low pass filter. 
Just glad he has it up and running stable now. Your right 543, having a Pi input like that does help clean up signal some.
Good to see you worked it out. The "L" network with just the coil and cap is frequently sufficient, but wasn't in this case. You went the next step to the "pi" network, which nearly always works. Just more effort to put in and get adjusted. Squeezing the coil turns closer, or spreading them farther apart can 'fine tune' the coil's inductance without shorting across a full turn.
If I had it down to 1.2, it would get a nail put in it, and move on the next challenge.
Congratulations and 73
If I had it down to 1.2, it would get a nail put in it, and move on the next challenge.
Congratulations and 73
@Shadetree Mechanic, I’m always asking a lot of your guinea pig post here, but when you get a chance can you give an update as to your final drive levels, power output and etc? Also curious if you played with the two trimmers at all, and if so, what results you had. Still need to rebuild mine...and this is a ton of help to me. You’ve made one heck of a reference post along the way.
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