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#1
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Open Loop aka Dipole bent into a square
Priz wrote:
"I`m working with attic antennas and need some help." The attic is a poor place for antennas but a good place to experiment. A 60-ft. perimeter is over one wavelength at 15 meters. According to Arnold B. Bailey`s "TV and Other Receiving Antennas" Fig. 8-14 on page 408, an open-circuit large loop has a radiation resistance of less than 80 ohms. A closed-circuit large loop has a radiation resistance of over 40 ohms. A closed-loop`s radiation resistance varies less with frequency than does the open loop. Borrow the book. Look at the chart. Pick the radiation resistance you want and proceed. Best regards, Richard Harrison, KB5WZI |
#2
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Open Loop aka Dipole bent into a square
I've got an update on my antenna experiment. I decided to buy a new
tuner, the MFJ 902H to see if that would help. It was priced low enough and had a built in balun. I tested it out using my SWR analyzer and this tuner was able to find matching points in the 80, 40, 30, 20, 17, 15, 12, and 10 meter bands. I did try to find a matching point on 160 meters but wasn't able to do so which is OK, since I've never worked 160 and the manual says not to try it on 160 anyway. I plan to put this antenna on the air over the weekend to see what it can do. I know it will be a compromise antenna but I'm hoping it will allow me to do what many other hams in my situation aren't doing, getting on the air. I also know all the jokes about MFJ, Mighty Fine Junk, Made from Junk or my personal favorite, Mississippi's Finest Junk, but it was priced right and when I got it, it appeared to be well put together. I'll let everyone know how it works out. Later... Priz |
#3
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Open Loop aka Dipole bent into a square
On Nov 16, 8:54 am, Priz wrote:
I've got an update on my antenna experiment. I decided to buy a new tuner, the MFJ 902H to see if that would help. It was priced low enough and had a built in balun. I tested it out using my SWR analyzer and this tuner was able to find matching points in the 80, 40, 30, 20, 17, 15, 12, and 10 meter bands. I did try to find a matching point on 160 meters but wasn't able to do so which is OK, since I've never worked 160 and the manual says not to try it on 160 anyway. I plan to put this antenna on the air over the weekend to see what it can do. I know it will be a compromise antenna but I'm hoping it will allow me to do what many other hams in my situation aren't doing, getting on the air. I also know all the jokes about MFJ, Mighty Fine Junk, Made from Junk or my personal favorite, Mississippi's Finest Junk, but it was priced right and when I got it, it appeared to be well put together. I'll let everyone know how it works out. Later... Priz The MFJ tuners are ok as long as you don't abuse them.. And on some , you probably should take the power ratings with a small bit of salt depending on the load you are matching. I've got a small MFJ random wire tuner that I've had since 1977. It still works, and I often use it as a mobile matcher. Also handy as a "line flattener" when running coax to a solid state rig. I've got a 989C that I got free from a guy that fried the coil. He was ignoring the instructions and running high power into a nearly half size dipole. I'm talking 8877 power.. :/ Started melting the coil form. Went through two of them. So he went out and bought a big Nye Viking, and gave me the 989C as basically junk.. To him anyway.. I messed with it a couple of hours getting the wires back in the right positions, and then resetting the roller tension, etc, and got it working again. I've been using it ever since. Well, when I use a tuner anyway.. I use the watt meter and antenna switch more than anything. It's rated 3KW, "dash of salt", but it will handle and tune about anything I will ever be messing with. Being it's a T network tuner, it's lousy for feeding half size dipoles though.. It will do 160m though. MK |
#4
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Open Loop aka Dipole bent into a square
wrote in message ... snip The MFJ tuners are ok as long as you don't abuse them.. And on some , you probably should take the power ratings with a small bit of salt depending on the load you are matching. I've got a small MFJ random wire tuner that I've had since 1977. It still works, and I often use it as a mobile matcher. Also handy as a "line flattener" when running coax to a solid state rig. snip I picked up a used MFJ tuner at a local ham swap meet. As is my wont, I took off the cover to give it the visual once-over before dumping any 'trons into it. Good thing. About six mounting and/or connection points - screws or nut/bolt combos -- were so loose as to guarantee problems. It's anybody's guess how long that stuff needed tightening. Was it ever tight? (hint-hint) "Sal" PS: The thing works pretty good, overall. |
#5
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Open Loop aka Dipole bent into a square
"Sal M. Onella" wrote in message ... snip I picked up a used MFJ tuner at a local ham swap meet. As is my wont, I took off the cover to give it the visual once-over before dumping any 'trons into it. Good thing. About six mounting and/or connection points - screws or nut/bolt combos -- were so loose as to guarantee problems. It's anybody's guess how long that stuff needed tightening. Was it ever tight? (hint-hint) "Sal" PS: The thing works pretty good, overall. The few MFJ items I have remind me of an old Ford Bronco II that I once owned. It was a piece of junk from day one, extremely useful, and reliable. With a little TLC it ran forever, and was the second best car I ever had. For example, my old MFJ CW audio filter is great, and has given over 20 years of service. But you don't want to look inside at the construction. |
#6
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Open Loop aka Dipole bent into a square
I put the antenna on the air last night and this morning and did make
a couple of CW QSOs. From Louisiana, I worked Virginia on 40meters with around 40 watts and Missorui on 30meters with 5 watts. Not great, but I'm getting on the air! |
#7
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Open Loop aka Dipole bent into a square
Priz wrote:
I've got an update on my antenna experiment. I decided to buy a new tuner, the MFJ 902H to see if that would help. It was priced low enough and had a built in balun. I tested it out using my SWR analyzer and this tuner was able to find matching points in the 80, 40, 30, 20, 17, 15, 12, and 10 meter bands. I did try to find a matching point on 160 meters but wasn't able to do so which is OK, since I've never worked 160 and the manual says not to try it on 160 anyway. ========================= You highly likely find a matching point for the 160 m band when you extend the twin feeder . The extension length to be such that from any end of the dipole to the matching unit the total length is roughly 1 or 3 or 5 etc quarter wavelengths .Any part of that feeder which is inside the shack can be coiled -up (kept away from a metal clad area). Frank GM0CSZ / KN6WH |
#8
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Open Loop aka Dipole bent into a square
Highland Ham wrote:
You highly likely find a matching point for the 160 m band when you extend the twin feeder . Sorry, with a feedpoint impedance with R in the units and X in the thousands, there is probably no length of feedline that will come close to being compatible with a tuner. No matter what feedline is used the SWR is way up in the hundreds to thousands. -- 73, Cecil http://www.w5dxp.com |
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