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1:1 balun construction
Here is one example searching Google for 1:1 balun
http://braincambre500.freeservers.co...r%20dipole.htm "JEFF UK" wrote in message ... Hi. I am now planning to put up my first dipole for SWL. I need help with; 1) A sensible length for general SWL.? I mostly listen between 80 and 20 mtrs. 2) I would like a diagram of a 1:1 balun construction. I believe this is the correct type for a dipole ? I have a ferrite rod not rings, will it work the same ? 3) I will be using 75 ohm tv coax to its feed point which is 90 feet from the house. Will this be ok ? 4) I will need to bend the legs of the antenna to fit them in the garden. I think this is ok for receiving ? All help welcomed Regards Jeff |
#2
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cheers guys 4 the info
"DxAce" wrote in message ... -=jd=- wrote: On Sun 14 Mar 2004 11:26:10a, DxAce wrote in message : [brevity snip] Absolutely correct. If one wants good single band performance then the dipole, or inverted vee configuration if just fine. But if you want a good 'all 'round' antenna then go the random wire, matching transformer route. I'm currently using the random wire(s), but I plan to put up an inverted Vee for 60 meters this summer. [brevity snip] I've seen the pic of a wire antenna on your web page and I was wondering if that's a current or outdated pic and is it your main antenna. It looks like it's strung on 4x4 posts - can't get a feel for the total length from the pic. The height from that pic seems like it's 10 feet (more or less) off the ground. 4x4x12's sunk 3 feet into the ground. That pic shows the antenna at 100' in length. It is now 200'. In the back, running at a 90 degree angle to the 100' wire pictured is a 70' wire. In comparison, my wire is strung (for the most part) 30 to 40 feet up following a more or less "Z" figure along the edge of the tree line on my property for about 300 feet. It's fed with coax through a matching transformer (grounded to the shield). The ground is about 20 feet from the transformer (the earliest point where I could ground it). Both my 70' and 200' wires are grounded at the base below the co-axial feedpoint. If you have additional questions which I've failed to answer (i'm sure I have), feel free to ask. Steve Holland, MI Drake R7, R8 and R8B http://www.iserv.net/~n8kdv/dxpage.htm |
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"JEFF UK" wrote. I am now planning to put up my first dipole for SWL. .............. let me ask first, why you especially want a dipole? Dipoles are great for directional broadcasting. Shortwaves come in from random reflection points only in the general direction of ..... there-to-there. :) Different frequencies will resonate best at certain angles from the antenna. 90-degree broadside is only for transmitted frequencies specific to the cut dipole lengths. 1) A sensible length for general SWL.? ............... for the range you specified, you might be well satisfied with 50-100 feet of wire. The idea is to get it as high as possible off the ground, and not threaded through trees. 2) I would like a diagram of a 1:1 balun construction. .............. Construction of a Balun for impedence matching is a matter of some patient engineering. Better to purchase one already made. A good one for use with 52 ohm coax will best be mounted at the top where the legs of the dipole meet, before signal travels down the coax to your RX. 3) I will be using 75 ohm tv coax to its feed point which is 90 feet from the house. Will this be ok ? ................. 75 ohm coax will be fine. Too much emphasis is placed on use of 52 ohm coax. Both are considered low-impedance. But, get 100% insulated shield. Braid, not aluminum sheath TV cable. Better, however, would be 600-ohm TV track wire for that distance. Cheap stuff. 600 Ohm is considered hi-impedence, and should enter the RX using that connection instead of the PL-259 Lo-Z input.... or feed it thru a passive tuner. See below. 4) I will need to bend the legs of the antenna to fit them in the garden. .................. Uh Oh! Yes, this will indeed affect impedence, freq response, as well as Mu factor and shape of Q. Consider, frequency response may be enhanced one way or the other by passing the signal through chokes or coils. Bending your antenna around corners "to make it fit" is essentially starting such a "coil" and the frequency response will be affected according to how much wire length you are using. Bottom line: Keep it straight, high, well insulated with propers hardware mountings. Feed your downlead end through a passive tuner such as a TUN-3 or TUN-4 then to the RX. GROUND the receiver chassis with THICK cabling, perhaps several strands of THICK twisted TV aluminum grounding wires. Go the shortest, most direct route to a real earth grounding rod, or bury a piece of concrete reinforcement grid underground to hook onto. |
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