working tward that as we're down to coax after the switch and antenna itself (it's new so unlikely)
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Please help your fellow skip shooter
- Thread starter lonestarbandit
- Start date
CMC - Common Mode Current
Like Unit_399 said, chances are the input impedance of your beam is further away from 50 ohms than your ground plane.
With the power you are running, you will need a CMC choke, line isolator, 1:1 current balun, (whatever you want to call it).
An easy one to make that may work is if you have ~16 extra feet of feedline (your coax going to the antenna). Get a 5" diameter piece of plastic (pvc well casing, etc.) about 6" long, starting on one end, close wrap 12 turns of your feedline around it, keeping the wraps tight and not overlapping. Wrap with electrical tape through the pipe to keep everything tight and in place. Leave enough coax on the end to connect to your beam's SO-239 and let the choke hang from your boom (use a strap or UV resistant zip ties. The idea is to get it as close (coax length wise, not physical) to your antenna connection as possible.
If you are lucky, this will be enough impedance to stop the CMC from coming down your coax shield and is a cheap fix. Problem solved.
In my experience, running the amount of power your big box does, this won't be enough impedance to block the RF. In that case, you can make your own or buy one that is already made for this purpose. There are many web sites that show how to make your own.
2 Comments:
1 - make sure your choke can handle double the watts that you are running through it (keeps the Ferrite from overheating).
2 - Make sure you have at least 5K ohms impedance at your operating freq. (27mHz). Otherwise, it isn't worth spending $$$ on it.
I roll my own , but these guys make a good product and are highly rated:
Good Luck!
Like Unit_399 said, chances are the input impedance of your beam is further away from 50 ohms than your ground plane.
With the power you are running, you will need a CMC choke, line isolator, 1:1 current balun, (whatever you want to call it).
An easy one to make that may work is if you have ~16 extra feet of feedline (your coax going to the antenna). Get a 5" diameter piece of plastic (pvc well casing, etc.) about 6" long, starting on one end, close wrap 12 turns of your feedline around it, keeping the wraps tight and not overlapping. Wrap with electrical tape through the pipe to keep everything tight and in place. Leave enough coax on the end to connect to your beam's SO-239 and let the choke hang from your boom (use a strap or UV resistant zip ties. The idea is to get it as close (coax length wise, not physical) to your antenna connection as possible.
If you are lucky, this will be enough impedance to stop the CMC from coming down your coax shield and is a cheap fix. Problem solved.
In my experience, running the amount of power your big box does, this won't be enough impedance to block the RF. In that case, you can make your own or buy one that is already made for this purpose. There are many web sites that show how to make your own.
2 Comments:
1 - make sure your choke can handle double the watts that you are running through it (keeps the Ferrite from overheating).
2 - Make sure you have at least 5K ohms impedance at your operating freq. (27mHz). Otherwise, it isn't worth spending $$$ on it.
I roll my own , but these guys make a good product and are highly rated:
CMC-130S-3K 1-30MHz – MyAntennas.com
myantennas.com
Good Luck!
Last edited:
As I am replacing this coax it is just about long enough as is, maybe 4 ft drip loop, the new coax will have plenty extra.
I will implement the wrap your own and try that as part of the new install once it arrived. Thanks guys.
I will implement the wrap your own and try that as part of the new install once it arrived. Thanks guys.
Help me understand how to "tie all grounds together"
1-I am putting up a new tower & will be utilizing 8' X 3/4" Copper Rod placed close proximity to ground tower w/ #4 AWG Copper Wire bout 12" long.
2-I get the Coax ground but want to come off of pole & under eave at about 8' Above grade. So do I bracket the PolyPhaser Coaxial Lightning Protector to the Steel Pole at 9' tuck under the eave then into garage where shack is. How do I "correctly" ground the Coax....MidSpan?? Do I have to meet Tower ground at base of tower??
Maybe I am overthinking this but want to do it right.
Station Ground I have none other than the Electrical System in the House.?
Any help would be appreciated. Thank You
Maxx Optimizer 60', 80-90' LMR400,
1-I am putting up a new tower & will be utilizing 8' X 3/4" Copper Rod placed close proximity to ground tower w/ #4 AWG Copper Wire bout 12" long.
2-I get the Coax ground but want to come off of pole & under eave at about 8' Above grade. So do I bracket the PolyPhaser Coaxial Lightning Protector to the Steel Pole at 9' tuck under the eave then into garage where shack is. How do I "correctly" ground the Coax....MidSpan?? Do I have to meet Tower ground at base of tower??
Maybe I am overthinking this but want to do it right.
Station Ground I have none other than the Electrical System in the House.?
Any help would be appreciated. Thank You
Maxx Optimizer 60', 80-90' LMR400,