Radio Shack 75-300Ohm Balum - HF ant info

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fourthhorseman

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I recently moved to where Ive got some elbow room.

Im looking for specs on using on of these baluns for a basic HF antenna.

What lengths would I need to RX around 80m +/ -...Or a link to some plans would be great!..
 
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902

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I recently moved to where Ive got some elbow room.

Im looking for specs on using on of these baluns for a basic HF antenna.

What lengths would I need to RX around 80m +/ -...Or a link to some plans would be great!..
Folded dipole around 1/2 wave total length - 65 ft each leg, 130 ft total (for 3.6 MHz - use 468/frequency, gives you the total length [1/2 wave] then divide by 2 for the leg length [quarter wave]). But unless you're really strapped like me, why not just get a Buxcomm balun and loading resistor and just put up a broadband loaded folded dipole? They aren't my choice for DX, but would be great NVIS antennas.
 

LtDoc

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The balun you have shown isn't going to work for your purpose. You really do not need a balun anyway.
- 'Doc
 

fourthhorseman

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Saw a write up regarding this balun,Using SDR Sharp,so Im thinking with the use of the HamItUp converter the set range of it wont matter..

Ive been looking at HF antennas for a while,,they all,to some degree incorporate a balun..Ive got some acreage now so I wanted to get a wire up to get better RX from about 12mhz to 5mhz or so..Not looking to go all in and get fancy..Just enough to move the can down the road so to speak,till Im better suited to install a proper (manufactured) longwire..
 

popnokick

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Can you post a drawing or pic of your planned antenna space on your property? Include buildings, poles, trees, and the positions, distances between, and height of each. Providing that info is going to enable much better recommendations to be made by the readers here on RR who have lots of experience and ideas.... IF they have enough info to work with.
 

Token

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Im all ears as far as a recomendation...
Theory and reality. If you get too wrapped up in the theory you never just try stuff, and if you just try stuff you will often find that things that are “wrong” still work quite well.

A simple half wave dipole does not require a balun, particularly for receive applications. To be sure, there are certain advantages to baluns, even 1:1 baluns, but really they are often not absolutely needed. The impedance of a half wave dipole (slightly shortened, say 0.48 wavelength) is only slightly off from 50 Ohm coax, and a good match for 75 Ohm coax, for practical purposes a match to both of these.

You can build a simple wire half wave dipole without a balun. As with all dipoles it requires an insulator at center (a simple 2 inch piece of 3/4 inch PVC water pipe with holes drilled near the end works for HF applications). Two pieces of wire (insulated, uninsulated, does not matter), each about one quarter wavelength long are attached to this insulator. The already mentioned formula of 468 divided by the frequency in MHz will get you close to the total (both sides added together) length. So for the phone section of 40 meters a person might choose 7.2 MHz, the example would be 468/7.2 = 65 feet total length, or 32.5 feet on each half. I find that you actually will end up shortening this slightly if you use the antenna for TX, but it is fine at that length for RX. Each piece of wire has another insulator at the far ends of the wires, again something as simple as chunks of PVC work fine. Coax is attached to the two pieces of wire at the center insulator, with the center conductor of the coax to one wire and the outer conductor to the other wire. Good electrical contact is required, say soldered, not just twisted together.

Such a simple dipole is not considered very wide banded, but should be adequate for receive purposes across a fair range of frequencies. Such a simple dipole might be higher noise (depending on location and other factors) than some other designs…but it is also much simpler, and almost the cheapest thing you can build.

If you want more bandwidth you can take the same approach but add multiple wires to each side, each different lengths (but in pairs, one of each length on each side), making a “fan” dipole. If you do this the sets must be insulated from each other, either by air gap and space or by electrical insulation.

Don’t be afraid to experiment. What is the worst that can happen, it does not work and you learned “ok, I am not going to do that again”?

T!
 
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