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Author Topic: balun or Unun help  (Read 1694 times)
KA4NMA
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Posts: 319




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« on: July 12, 2014, 05:35:26 PM »

I have a ft-817 and a LDG 817 tuner as a portable system. I am  planning on using this system with a doublet (about 40 ft of wire that could  be configured as a doublet, vertical with 1 radial, inverted L, etc).  The wire comes from what I have in my junk box.  I am also thinking of getting one of the MFJ telescoping whip with a ground spike and using the 2 40ft wires as radials.  Bands would b e 75m-6m. I am looking for a balun or uunun for my system to help with matching. What would you suggest? I am disabled so building things are difficult.  Can somebody help me out?

Randy ka4nma
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KB1GMX
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Posts: 745




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« Reply #1 on: July 12, 2014, 06:54:35 PM »

I'd suggest the Elecraft switchable balun.  little big for a ft817 but good.

As to 75 though 6.... 

On 6M (SSB/CW OR FM) antenna height is important as well as vertical only works for
FM where SSB/CW is better with horizontal polarization.

Go for 75 through 10.  Even for those 40ft is too small without a loading coil for 40 (33ft= 1/4wave)
and really short for 75 (66ft= 1/4 wave).

Verticals need length or load coils to make up for the lack of it.  That and ground radials to make it work.

Since you have the LDG817 a balun or unun is really not needed unless you need to isolate the line
then a unun will do.

33.5ft of wire as a doublet would make a fine half wave dipole for 20M.

Trying to cover all bands usually means most are compromised.  With an FT817 a good antenna make
the whole low power thing more enjoyable.  You might consider a LNR(PAR) EF40/20/10,  Yes, its
only three bands but the best three for most activity.  I use one with my ft817 (no tuner or balun required)
and 25ft of coax for portable/field use.  I have two one is permanently install at the house and I run it up
to the rated 25W as a main HF antenna for those bands.


Allison


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N7EKU
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Posts: 61




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« Reply #2 on: July 15, 2014, 10:18:12 PM »

Hi Randy,

If you could give us more details, I think we could give you a lot better guidance and ideas...

Can you tell us what kind of operating and what kind of surroundings you will have?  For example, will you have natural supports around?  How are you thinking of getting the ends and center of your wires up?  Are you looking for nearby states contacts or DX?

All these will make a big difference in what you want and can do for choosing an antenna.

Allison's advice on the endfed is good.  Three active bands, good for different time of the day, and you only need one high support for one end :-)  I have heard a lot of OM's are happy with them.

But designing and making your own can be quite satisfying (and cheaper!)  For example with a 5M long whip that you can adjust to 1/4 or 5/8 wave on 6M-20M, with your two 40' wires hooked in the center to make four 20' ground radials, you can have a nice DX antenna that's easy to put up/take down and can be used for places without trees.  And verticals can be the cat's meow at the beach where the saltwater ground plane is so excellent.

Have fun and 73,


Mark.



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