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Message |
    
Marconi
Intermediate Member
Username: Marconi
Post Number: 481
Registered: 11-2001
| | Posted on Thursday, November 10, 2005 - 11:04 am: | 
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Will a suitable ground plane alone, that is appropriately attached to a 1/4, 1/2, or 5/8, wavelength radiator, decouple the coax from the feed point in order to prevent common mode currents? |
Narf_edwards
Junior Member
Username: Narf_edwards
Post Number: 24
Registered: 3-2005
| | Posted on Thursday, November 10, 2005 - 1:38 pm: |
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Add a coax balun....18-21 feet of rg8X wrapped around a 4" form.This will get rid of rf in the feedline.Attach at base of antenna.Add another at the entrance to the shack if you like.They work great for me
Narf |
Bruce
Senior Member
Username: Bruce
Post Number: 3210
Registered: 9-2003
| | Posted on Thursday, November 10, 2005 - 5:52 pm: |
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Yep the old coiled coax trick nice and wide band too..... |
Chad
Advanced Member
Username: Chad
Post Number: 562
Registered: 11-2004
| | Posted on Thursday, November 10, 2005 - 8:08 pm: |
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Would I really need to use 18-21 feet? How long would this 4" diamater chunk-o-PVC have to be to accomodate 18' of RG8X without me having to do the math 
I've been thinking about this and thinking it might eliminate the "PC speaker" bleed thru.
Chad |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 821
Registered: 9-2004
| | Posted on Friday, November 11, 2005 - 12:29 am: |
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if each coil of coax (assuming 1/2" dia. RG8 etc.)
uses 12.5 inches to wrap around a 4" form, then
approx. 19 wraps would be approx. 20' of coax.
so for simplicity's sake, we use 20 wraps, at 1/2" each and that gives us approx. 10 inches total.
i would go with 14-16" of PVC.
i have one about 23' down from the feedpoint, but i used a 10" form. i heard the size of the coil was supposed to be 8" to 10", and about 8 to 10 wraps.
can we get some definitive clarification on this please?
the answer is in Lou Franklin's book, "UNDERSTANDING AND REPAIRING CB RADIOS"
i just dont have a copy anymore. (gotta get one!)
later,
matt |
Narf_edwards
Junior Member
Username: Narf_edwards
Post Number: 25
Registered: 3-2005
| | Posted on Friday, November 11, 2005 - 7:23 am: |
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I use the thin walled white plastic pipe used for drains.About 8-10 inches long with tyraps to hold coax to form.Add an extra tyrap to hook on to base of antenna for strain relief
Narf |
Tech833
Moderator
Username: Tech833
Post Number: 1088
Registered: 8-2002
| | Posted on Saturday, November 12, 2005 - 10:21 am: |
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It is much easier to attach several snap-on ferrites to the cable at the bottom of the antenna, and works better too.
To answer your question directly, Marconi- No. Not always. |
Narf_edwards
Junior Member
Username: Narf_edwards
Post Number: 26
Registered: 3-2005
| | Posted on Sunday, November 13, 2005 - 5:43 pm: |
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Check this out |
Chad
Advanced Member
Username: Chad
Post Number: 568
Registered: 11-2004
| | Posted on Monday, November 14, 2005 - 10:03 am: |
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Mine is almost done. It is 3"PVC Poo Pipe, used... YUCK Wrapped with belden RG8X. The ends feed inside the pipe via holes drilled at angles to keep wire stress down. Holes were drilled on the leading edge of the coax hole to accommodate a Nylon tie for securing the coax. On the top and bottom there will be PVC caps the bottom cap will have a 239 female connector and a Buryflex whip coming out. This will accommodate a one trip climb. I plan to then make a collar out of 1" of the same PVC to make a collar and keep water from running to the connector, (like the Imax collar) Standoffs are going to be smaller PVC notched and held to the mast and ugly balun with hose clamps. All holes are sealed inside and out with aquarium 100% silicone sealant after hot glue was used as a first seal.. So far price = $0 from scrap stuff. A trip to Lowes for the caps and clamps will probably bring to total price to under 10 bux. I'll get pics, should be finished tonight.
Chad
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