|Joined:||Sat, Apr 7th 2012, 19:22||Roles:||N/A||Moderates:||N/A|
|Twin Lead and metal mast?||Oct 31st, 16:12||2||145||on 31/10/14|
|Dipole or loop?||Aug 19th, 03:02||11||576||on 5/9/14|
|dBmicrowatts?||Jul 16th, 19:51||3||289||on 17/7/14|
|Dipole crossing vertical?||May 2nd, 00:01||3||341||on 5/5/14|
|Ground Plane antenna near metal roof?||Jul 6th 2013, 15:28||4||1,459||on 9/7/13|
|Does paint affect a Yagi?||Jan 17th 2013, 02:40||4||860||on 25/1/13|
|50 or 75 ohm reference for analyzer?||Jan 6th 2013, 22:52||2||823||on 7/1/13|
|Using ladder line with Yagi||Jan 2nd 2013, 00:58||1||895||on 2/1/13|
|Two new ham questions about antennas||Dec 9th 2012, 16:56||7||1,883||on 26/12/12|
|Twin Lead and metal mast?||KO0Y||on 31/10/14|
|I bought a dozen of those army surplus four foot aluminum poles and plan to use them to hold up the center feed point of a long non-resonant dipole (260'). Well, it might be more of an inverted v since the ends will be 20-25' off the ground, and the center twice that.
I will use 300 ohm twin lead for the feed line back to a balun in the shack. I know that the feed line should leave the dipole at a right angle. My question is whether I can run the line down the mast, or if it needs to run away at a right angle to both the antenna and the mast? Thanks for advice.
|Dipole or loop?||KO0Y||on 1/9/14|
|I shortened the feed line by about 14 feet, which did shift the impedance curves upward enough to make the 4.2 MHz region easier to tune. I wish I could attach those graphs here, but doesn't seem possible. Two dipoles would be better, I can see, but that is a project that will have to wait. Thanks again for all comments; I'm beginning to understand this a bit better now.|
|Dipole or loop?||KO0Y||on 27/8/14|
|I bought a 1:1 maxi-core balun from DX, and (for now) left everything else the same(150 foot dipole, 90 feet 300 ohm twin lead to shack). I used a RigExpert to measure SWR and Z with this balun.
From 2 to 10 MHz, more than half of the range is 200 ohms or lower, so I guess it's good that I didn't get the DX 4:1 balun. Z peaks at 1200 ohms around 4.2 MHz, which is unfortunately near my primary MARS frequency. I notice that it is difficult to tune there, and cannot get SWR much below 2:1.
The antenna is resonant at 3.62 MHz, which is higher than the length of 150 feet would suggest. Is this because it is low (22-24 feet) off the ground?
I could hang a longer dipole, but not higher. DX suggests 220 feet for a multi-band non-resonant antenna, and I could go as long as 260 feet. Would that shift the impedance peak, as well as resonance, downward?
|Dipole or loop?||KO0Y||on 19/8/14|
|Thanks, Nate. My understanding now is that the function of ladder line is to reduce loss on long runs from the shack. Since it is only 90 feet at most, it would be better to hang a balun at the center point (which is supported by a mast), and use 213 coax from there. Please correct me if this is wrong.|
|Dipole or loop?||KO0Y||on 19/8/14|
|Thanks, Zack; I'll continue with the dipole and just replace the feed line. I am planning to use one of the Comtek baluns sold by DX Engineering; these have excellent reviews on eham, and seem well-constructed. Their site recommends 1:1 for dipole, but you are saying that may supply out-of-range impedance to the tuner.
I also have a mechanical tuner (MFJ-949E) and that will tune a broader range, but it is slower, and I can't use it with ALE. So I guess my question would be: how much power might I give up for the convenience of the auto-tune? By the way, I operate at 100 watts with no intent to use an amp. Thanks again for advice.