Closed loop antennas

[rocketjok]

Hi, I am looking for some information on closed loop antennas for NVIS shots. I remember the antenna from the course but it's been a while and HF is sketchy in this part of the world. Here are some specific questions I had that I was hopeing could be answered.

1. If I use my balon from my 137 kit I can plug one end of the wire to the balon. But how do how do I cut the antenna to freq and connect the end that's wrapped on the bobin to the balon.

2. Will the balon from the basic antenna kit bags(same as echo course) have the correct feed point impedance for the closed lookp?

3. I have been researching using ladder line as a transmission line. Would all I have to do is connect the ladder line to the ant. and ground post on the radio?

I am prepared to go buy some 16 awg insulated wire and cut it to the middle of my MUF. Then just wire that to the balon or transmission line. Any thoughts on this? it would certainly make traveling simpler.

I have been looking around the Web and the sites seem to skip over this junction because they just use wire pre cut to freq.


My base station is under a 100 miles and the area is mountain's and it will be ALE . If there is any advice I am open to it. I appreciate any help.

[glebo]

Originally Posted by rocketjok

Hi, I am looking for some information on closed loop antennas for NVIS shots. I remember the antenna from the course but it's been a while and HF is sketchy in this part of the world. Here are some specific questions I had that I was hopeing could be answered.

1. If I use my balon from my 137 kit I can plug one end of the wire to the balon. But how do how do I cut the antenna to freq and connect the end that's wrapped on the bobin to the balon.

You can connect the wire on the other post of the balun, ya just have to figure out how The formula is 1005/freq mhz. just divide the answer by 4 for your 4 sides.

2. Will the balon from the basic antenna kit bags(same as echo course) have the correct feed point impedance for the closed lookp?

I don't know what the ratio of the balun you have from your kit is, but the SORAK kit had two, I belive a 1.5:1 and 9:1. The Full Wave Loop feed point impedence is higher that a doublet, approx 100 ohms. You can try the two baluns and see what SWR you get. They won't be a perfect match, but one may do better than the other.3. I have been researching using ladder line as a transmission line. Would all I have to do is connect the ladder line to the ant. and ground post on the radio?

I am prepared to go buy some 16 awg insulated wire and cut it to the middle of my MUF. Then just wire that to the balon or transmission line. Any thoughts on this? it would certainly make traveling simpler.

If you're using the 137 (in ALE), that should do ok

I have been looking around the Web and the sites seem to skip over this junction because they just use wire pre cut to freq.


My base station is under a 100 miles and the area is mountain's and it will be ALE . If there is any advice I am open to it. I appreciate any help.

Also, just try a good 'ol doublet...

[69harley]

Yep, hard to beat a low hanging doublet for NVIS work.

[rocketjok]

I will try the doublet. I rode the pallet so I have a week to make test shots around the area. I wanted to try using the close loop because the base station is under 40 miles and I wanted to have better control of my take off angle. I will be making shots all week, I appreciate the input. last year teams had a rough time using HF and i don't want to be one of those teams.

[Peregrino]

Try the low doublet (< 1/4 WL above the ground) and run a reflector (ground plane/counterpoise/std yagi). The reflecting element is 5% longer than the driven element and is located 0.15 wavelengths behind/below the driven element. Read the following article to confuse the hell out of yourself: https://www.txarmymars.org/downloads...and-Design.pdf This article is specific because it focuses on MARS freqs and you'll probably be operating "in the vicinity".

[albeham]

(length = 1005/MHz) and laid the antenna horizontal about 1 foot off the ground.

Used a lot of loops, and yes a dipole about a 1 foot off the ground will work also.

Reverse scissors antenna works great. A dipole with the radiating side is closed over the ground side, like a pair of scissors, with the opening of the scissors pointed away from the base station.

I do hope the base station has a NIVS type antenna as well.

AL

[Paragrouper]

I would agree with others on the doublet. it is a reliable choice and, depending on your other planned activities, simple to construct. frequency selection will be critical and I would review those with the base if possible. as a rule of thumb for NVIS, they should run between 6-8 MHz during the day and as low as you can go and stay above the noise at night, ~3MHz