Broadbanding a Dipole?

[WA2SQQ]

I’d like to ask your opinion on an idea I had last night about how I might create an 75m antenna that is more broad-banded than the inverted V I’m using. Multi-band dipoles operate on the principal of multiple lengths of wire, each resonant at different frequencies.

Could I build a dipole, using ladder line as the elements, and cut one side for the low end of 75 and the other end for the high side? Would these two parallel wires effectively act as two separate antennas and extend the usable bandwidth?

[flintstone mop]

Design / build a dipole as long as you can get it, and feed it with old fashioned Open Wire Line / ladder line, and a good wide range tuner.

If memory is working: 3/8 wave on the lowest freq you intend to use, even if the ends droop down a little.

I have been using my full length dipole on 160 -20 meters, fed by OWL and a Dentron 3KA tuner. The dipole is 60 feet in the air.

[WA2SQQ]

It's what I'd like to do, but it's not feasible for me to run the open wire into the shack. I'd also prefer having a self resonant antenna. The tuner is only going to fool the transmitter.

[VE3ELQ]

I’d like to ask your opinion on an idea I had last night about how I might create an 75m antenna that is more broad-banded than the inverted V I’m using.

My friend Howard K2AQ who I often chat with on 80M is using such an antenna.  I dont have the exact details but I believe it has a second parasitic wire element spaced below the driven element and is near flat across the entire band. He is good in QRZ and would probably provide you the details. If not I will get it from him and post here if requested.
73s  Nigel

[W1ITT]

ON4UN's Low Band DXing, Fifth Edition, from the ARRRL, shows a broadband dipole in chapter 8, section 1.4.1.  It stays below 1.8 SWR across the 80/75 meter band, with most of the range averaging 1.5 or so.  It uses the "open sleeve" technique, with an extra wire closely coupled to the driven part of the antenna. It's N6LF's adaptation in a practical form, and ends up with coax into the station for those who are unable to deal with good old open wire balanced line.
The ON4UN series is my favorite reference for low band antennas, and is one of the League's better efforts, worth the money.

[WA2SQQ]

I’d like to ask your opinion on an idea I had last night about how I might create an 75m antenna that is more broad-banded than the inverted V I’m using.

My friend Howard K2AQ who I often chat with on 80M is using such an antenna.  I dont have the exact details but I believe it has a second parasitic wire element spaced below the driven element and is near flat across the entire band. He is good in QRZ and would probably provide you the details. If not I will get it from him and post here if requested.
73s  Nigel

I just reached out to Howard. Thanks!

[WB2EMS]

Another idea might be to connect a second inverted Vee or dipole elements to the feedpoint, at right angles to the existing elements. Tune one for the high end of the band and the other for the low end. I just got done repairing my lightning zorched 40/60 meter antenna built like that, and used to have a 160/80 meter antenna built that way. There might be some interaction with close frequency spacing between the two antennas, but being at right angles will help minimize the coupling. I think I've seen that done in a commercial or mil antenna.

[KD6VXI]

If broadbanded low swr,  instead of flat swr is what you are looking for,  mismatching the coax helps.   Ie,  feed a 50 ohm antenna with 75 ohm coax.   You will not get a 1:1 anywhere,  BUT the 2:1 points stretch.

This is due to the increased loss,  IMO.

Also,  swr can usually be improved across a large swath by increasing feed point R.   Use a folded dipole,  at 2 to 3 hundred ohms and a coass balun for band of interest.

To answer your question directly now,  I had the same idea.   I modeled it a while back in manna.   I found that it did help spread the 2 to 1 points.   I wasn't sure if it was due to the swr of each individual dipole or because it just made the elements look fatter.   I used fairly close spacing,  using extra home made ladder line spacers (probably 6 inch).

Hope it helps.

--Shane
KD6VXI

[Pete, WA2CWA]

I’d like to ask your opinion on an idea I had last night about how I might create an 75m antenna that is more broad-banded than the inverted V I’m using. Multi-band dipoles operate on the principal of multiple lengths of wire, each resonant at different frequencies.

Could I build a dipole, using ladder line as the elements, and cut one side for the low end of 75 and the other end for the high side? Would these two parallel wires effectively act as two separate antennas and extend the usable bandwidth?

The simple way to broadband a dipole is to make it fatter. Using ladder line as the antenna elements will generally make the antenna broader over a single wire element. A typical cage dipole consists of 4 identical lengths of wire in each dipole element and separated by 90 degrees. A cage dipole probably could be fabricated from two sets of identical ladder line if one can figure out a simple way to attach the spreaders of each ladder line to keep the lengths of the wire parallel and 90 degrees from each other. The ends of each ladder line are attached to each other. A matching transformer, typically a 1/4 wave length of 72 ohm coax should be used between the antenna feed point and the coax going to the station.
This link might provide some further insight: www.qrz.ru/schemes/contribute/arrl/chap9.pdf

Cage dipole fed with open wire line but matching transformer and coax could also be used:

[WB4AIO]

I’d like to ask your opinion on an idea I had last night about how I might create an 75m antenna that is more broad-banded than the inverted V I’m using. Multi-band dipoles operate on the principal of multiple lengths of wire, each resonant at different frequencies.

Could I build a dipole, using ladder line as the elements, and cut one side for the low end of 75 and the other end for the high side? Would these two parallel wires effectively act as two separate antennas and extend the usable bandwidth?

I built a broadband 75 meter inverted vee as follows:

It is two inverted vees at right angles to each other, fed from the same coax. One is cut to resonate at about 3620 kHz and the other at about 3910 kHz. (Make them a bit longer than you need and trim in the field.) In my case the feedpoint was about 50 feet in the air and the ends at 20 feet up.

The results were excellent -- under 2:1 SWR from 3.5 to 4 MHz, and great signal reports out to 2,000 miles away. Modeling shows that this antenna is almost perfectly omnidirectional too, noticeably more so than a plain inverted vee.

I built this antenna for a friend, but want to build one for myself too!

73,

Kevin, WB4AIO.

[WA2SQQ]

Thanks to all - got some good ideas. I'll let you know what I ended up with and how it works

[flintstone mop]

I’d like to ask your opinion on an idea I had last night about how I might create an 75m antenna that is more broad-banded than the inverted V I’m using. Multi-band dipoles operate on the principal of multiple lengths of wire, each resonant at different frequencies.

Could I build a dipole, using ladder line as the elements, and cut one side for the low end of 75 and the other end for the high side? Would these two parallel wires effectively act as two separate antennas and extend the usable bandwidth?

I built a broadband 75 meter inverted vee as follows:

It is two inverted vees at right angles to each other, fed from the same coax. One is cut to resonate at about 3620 kHz and the other at about 3910 kHz. (Make them a bit longer than you need and trim in the field.) In my case the feedpoint was about 50 feet in the air and the ends at 20 feet up.

The results were excellent -- under 2:1 SWR from 3.5 to 4 MHz, and great signal reports out to 2,000 miles away. Modeling shows that this antenna is almost perfectly omnidirectional too, noticeably more so than a plain inverted vee.

I built this antenna for a friend, but want to build one for myself too!

73,

Kevin, WB4AIO.

Something to be said for inverted VEE's. High apex and the ends high as possible from the ground. Neat idea of two resonant antennas sharing the same feed line.

I fed my OWL through a hole in the wall, through the siding and had a shelf for the tuner on the same wall. Coax into the radio room. 20 foot walk to the tuner. I have no problems with QSO's on 160M with this set up. Running QRO on AM.