Re: How to MATCH a 50 Ohm antenna/coax to 75 ohm Coax/hardline

[ssbothwell SWL]

i'm aware that i would have to use a different antenna on 160m. i was hoping to have only one transmission line up to the roof and then rig up a switching system so i can connect different dipoles to the one coaxial line. will a sleeve balun that is long enough for 160m also work on higher frequencies?

You can buy sleeve balan (often called W2DU) kits. Suggest you go with one of those  to keep it simple at the start. You can always build your own later. The standard kit is good for 80-10 meters. Making it work on 160 is just a matter of adding more toroids. Keep in mind, a coax fed dipole can only be used on one band¹ anyway, so to cover 80-10, you'll need several dipoles or have to go with an open-wire feedline.

1- Actually, a dipole can be used pretty effectively on odd-harmonics (e.g. a 40 meter dipole can also be used on 15 meters), but you may have a higher SWR than on the fundamental.

holy cow thats a lot of responses! thanks everyone for all the information. sounds like a ferrite sleeve balun would be pretty easy to setup. do i just use whatever torroids have a nice fit over my coaxial cable? how long should i make the sleeve?

will the same sleeve function properly on a variety of bands? eventually i want to get on 160m, but i believe its not allowed on a technician class license.

[Steve - K4HX]

Yes.

will a sleeve balun that is long enough for 160m also work on higher frequencies?

[K1JJ]

Interesting on the 6M past and future plans, Carl.  Good thing you swapped out those insulators. The Delrin rod will work out FB.


Almost ready for 20M and 10M AM here. Today I took down a 40M south wire Yagi that was blocking the "rope" rotation of both the 20M and 10M Yagi stacks. So now I will be able to beam west USA.  Also need to get the amp tuned there.  Hope to make some posts soon of calling CQ west on 14.330 and 29.000 mhz AM.

T

[ssbothwell SWL]

hi guys,

i just ordered a 1:1 current balun, rated at 1-30MHz, from the wireman. i have a couple final questions related to impedance matching.

1. i have some RG6 (75ohm) and RG8x(50ohm) cables. which one should i use for hooking up my halfwave dipole antenna? in other words, is it better to have the cable matched to the antenna or to my transmitter?

2. what is the best way to hookup my antenna to the uhf connector on my transmission line?

i was thinking of making a little box that has a uhf input and then splits the shield and centerwire of the input into the center points of two uhf connectors as outputs to the two halves of the dipole. however, it seems like a little bit of overkill to buy a project box and the connectors to do that. is there some kind of pre-fabricated splitter that does this?

[Steve - K4HX]

I'd go with the RG-8X. There is nothing wrong with RG-6 but most of it has an aluminum shield that can be more difficult to solder than the copper shield on RG-8X.

There are tons of prefab center insulators out there. Two are at the link below. You can make your own with PVC pipe. Some guys just loop the coax over the top of a typical end insulator and secure it with a tie-wrap. Then you solder the center and shield to the two legs and seal everything up with liquid tape. Pick your poison and have fun.

http://www.radioworks.com/cinsul.html

[ssbothwell SWL]

cool thanks for the link. its not problematic to be tying the antenna in a loop at its endpoint?

[Steve - K4HX]

Most certainly not the wire portion of the antenna. But, you wouldn't want to tie the coax in a knot. Some people loop the coax over the center insulator and keep if in place with a cable tie. I've never done it myself and don't think it would be a good idea with some types of coax where the center conductor can migrate through the foam dielectric. It is a very inexpensive way of making a center insulator though and that's the only reason I mentioned it - options. I'd personally go with a purpose build center insulator.