OCF Dipole And Ground Plane Antennas On A Push-Up Mast
I am often asked, “what is a good first antenna for use on the HF bands”. This is a difficult question to answer and there is no one answer which is best for everyone who asks this question. For example, a HAM in a restricted HOA situation will have a much more limited set of choices than a HAM with a small lot and some trees. The restricted HOA situation is often a very difficult one and is usually best solved with an HF antenna such as a Buddipole that can be put and taken down easily. For this post, I am going to concentrate on some choices for HAMs with a small lot and perhaps a few trees. The picture above shows my first real HF antenna system (it also included a VHF/UHF ground plane antenna for 2m and 70cm repeater access).
In my mind, the best HF antenna for a new HAM should have the following characteristics:
- It should be inexpensive
- It should be relatively easy to put up
- It should be somewhat stealthy so as to be neighbor and XYL/OM friendly
- It should handle at least 100w of continuous power (I think the new HAM does best with this level of power as it provides more breathing room while the operating technique is being learned)
- At a minimum, it should cover the 20m band and ideally should also cover 40m as well as some of the higher frequency HF bands (I consider 20m to be the most important HF band for the beginning HAM as it allows working both DX and domestic contacts, has many big guns which will be easier for the little pistol HAM to work and is of a manageable size)
- It should be reliable and stay up year-round without a lot of maintenance
*** DISCLAIMER – The author assumes no liability, warranty or responsibility for the safety, possible injury, reliability or function of the antenna installation methods, materials, techniques and systems discussed in this post or anywhere else in this Blog or for any injury or consequential losses, injury or damages resulting from or incurred in connection with the use of the information presented here. Antenna work is potentially dangerous and can result in serious injury or even death. These ideas worked for me but may not work for you. You decide to use the ideas suggested here you do so entirely at your own risk. ***
I am going to talk about two different antenna systems that will meet these goals – an Off-Center Fed (OCF) Dipole and a Vertical Dipole. Some might say that vertical antennas should be on this list as well but I find them to be more complex to install properly and therefore are not, in my estimation, the best first antenna for a new HF operator.
My first antenna was an OCF Dipole from Buckmaster which covers 80m – 10m (15m excepted). This antenna is a good performer and I was able to work and confirm about 125 countries on multiple bands with it. This antenna is very well made and I still use it for domestic contacts and some DX at my QTH. The OCF dipole is a multi-band wire antenna that does not use traps and is a relatively simple install.
Buckmaster OCF Dipole Installation Diagram (Courtesy Buckmaster)
The OCF dipole is usually installed in an inverted-V configuration so the ends do not need to be very high off the ground (~10 ft is good). The center should be 35 – 45 ft up and must have a reasonably solid mounting point to support the weight of the center matching balun and feedline. The best approach is to suspend the balun/feedline combination from a tree limb if one is available in the right location.
Guying Arrangement Looking Up The Mast
In my situation, I did not have a suitable tree in the correct location so I installed a 50 ft heavy-duty fiberglass push-up mast (only extended to 42 ft – see below for details) on the side of my house to provide the needed center support. The push-up mast came from Max-Gain Systems, Inc.
Mast Guy Anchor On Ground
As you can see from the photo above, the mast is guyed at two levels with a 3-point guying system made from 0.188″ synthetic rope from DX Engineering. One pair of the guy ropes is anchored on the ground using a large, screw-in earth anchor from DX Engineering.
Mast Guy Anchor On House
The other two sets of guy ropes are attached under the eves of my house using sturdy anchors built from 2″x6″ and 2″x4″ pressure-treated lumber. NOTE THAT ALL OF THE ANCHORS MUST BE SOLIDLY MOUNTED IN THE GROUND OR ATTACHED TO STUDS IN THE HOUSE STRUCTURE. I cannot stress enough how important it is to ensure that guy attaching points are solid and will hold up. A mast of the type shown here will not be stable without proper guy ropes and anchors and it will collapse if the guy system is inadequate or if it fails. I used a 50 ft mast but did not extend the top section very much (only a foot or so to mount the balun for a total height of about 42 ft) to ensure that there was a sold mount for my antennas (note that the top guy attaching ring from MGS is just below the point there the OCF dipole’s balun attaches to the mast with two stainless steel hose clamps – this ensures a stable mounting point for the balun).
Push-Up Mast Anchor To House
The mast is fastened to the house about 18 ft up from the ground with a block and a piece of galvanized strapping material that is securely fastened to the framing of the house with lag bolts. Once the antenna’s balun and feedline are installed on the top of the mast and the guy ropes are in place, the mast can be pushed up into position with the help of three helpers – one on each pair of guy lines. The helpers are essential to ensure that the guy ropes can be maintained with enough tension to provide support for the mast and to keep it stable as it is pushed up. The feedlines (I used LMR-400 UltraFlex coax) are taped to the mast every few feet as the mast is pushed up.
Mast Section Locking Clamp
The MGS mast has plastic clamps to lock each section of the mast in place as it is pushed up. I have found that after continuous exposure to the sun and the elements, these clamps can break if they are made tight enough to hold the mast locked over long periods of time. To solve this problem, I install a stainless steel hose clamp at each mast section joint after the section is pushed up to its extended position. This locks the section securely without requiring excessive tension on the plastic locking collars.
Mast Base And Feedline Conduit
It’s also important that the base of the mast has a solid point to rest on and not be able to move around. To accomplish this, I made a base out of several heavy 2″x8″ sections of pressure-treated lumber. The upper piece of 2″x8″ lumber is drilled with a hole saw to provide a hole for the mast to sit firmly in and the blocks are held in place on the ground with several large galvanized 18″ spikes. I also opted to install plastic conduits in the ground to route my feedline from the base of the antenna to the entrance of my shack. The feedline is also connected to a well-built earth ground via an Alpha-Delta surge projector prior to entering the shack. I also strongly suggest disconnecting your feedlines prior to them entering your house during times of potential lightning activity or when your station is not in use.
Antenna Feed Point Connection Details
The last area to note is the proper way to install the feedline where it attaches to the antenna. You are trying to accomplish two things here – first, to provide a drip loop so that water does not run down your coax and second to provide a means to create a high impedance choke to block any RF that might flow on the outside of your feedline. The later is not a big problem with the Buckmaster OCF dipole as it uses a high-quality balun for matching and decoupling at the feed-point. It’s also important to seal the connections between the antenna and the feedline at the connectors. To do this, I use a combination of CoaxWrap and Super 88 Electrical Tape (wrap the connection and connector shell with one layer of electrical tape first, then a layer of CoaxWrap, then a final layer of electrical tape for protection). The upper antenna in the picture is a Diamond X-300NA ground plane vertical antenna that I have installed on my mast for accessing local 2m and 70cm repeaters.
Dipole Antenna End Anchor
Once the center of the OCF Dipole is up and the feedline supported, one needs to anchor the two ends. I used a couple of pulley’s attached to two sturdy trees near the ends of my antenna. I used the same synthetic rope attached to the insulators on the ends of the OCF Dipole to provide support for the ends of the antenna. Note the use of rubber tarp stretchers to provide tension on the support ropes. I have found that this system works quite well and keeps the antenna supported without breaking or excessive sagging as the trees sway with the wind. You do not need to make the end supports extremely taut – a little bit of sag in the antenna wire is OK and a slight amount of slack will reduce the stress on your antenna in the wind.
The only maintenance required with this sort of antenna is to inspect the coax and adjust the tension on the guy ropes and end supports periodically. I do this simple maintenance twice a year in the fall and in the spring.
20m Vertical Dipole – A Stealth Antenna For DX Work
Can you find the antenna in this picture? It’s a 20m vertical dipole located just to the right of the tree at the center of the picture. This is one of the simplest and least expensive HF antennas to install, is stealthy and it works very well. Its radiation pattern exhibits a low takeoff angle which makes it an excellent choice for DX work and it will exhibit a reasonably low SWR across the entire 20m band. All you need to build this antenna is an inexpensive 20m dipole antenna, some rope and a tree limb that is about 38 feet or so from the ground.
Vertical Dipole Anchors At Base
Instead of installing the dipole horizontally, you install it vertically with one end about 2-3 ft off the ground using a rope (ideally with a pulley) to support the other end from a tree limb. about 40′ up. Note the use of the rubber tarp stretchers to maintain a modest amount of tension on the ropes attached to the ends of the dipole.
Vertical Dipole Anchor At Antenna Feed-point
Before pulling the antenna up, attach a suitable length of lightweight feedline (RG8X coax cable works well) to the feed-point of the dipole. Don’t forget to seal the connection with a combination of CoaxWrap and Electrical Tape. You will also want to attach a piece of synthetic rope at the feed-point at well. Once the antenna is pulled up into position, anchor the feedline to the ground so that it slopes away from the antenna’s vertical section at approximately 45 degrees. Then fasten the feed-point rope to the ground opposite the feedline so that it pulls the vertical section of the antenna straight (without the feed-point rope, the weight of the feedline and the 1:1 balun at the feed-point will prevent the antenna from being a straight, vertical radiator). As explained with the OCF Dipole previously, it is important to properly ground the feedline before it enters your house and to disconnect the feedline when lightning might be present and when your station is not in use.
As with the OCF dipole, this antenna’s feedlines and support ropes should be checked and adjusted twice a year. Given this is such an effective and simple antenna, you might ask “why not always use a vertical dipole”? The biggest drawback is that it only will work on a single band. It’s also difficult to put up one of these for 40m (you’d need a tree limb about 70 ft high and a safe way to get a rope over it). Some hams do put several vertical dipoles up at different spots on their property and this makes an excellent and simple multi-band antenna system.
I hope that this post provides some useful ideas for HAMs contemplating the installation of their first HF antenna. As noted by Rick (W1RAG), a combination of an 80m – 10m OCF Dipole and a 15m Vertical Dipole would cover almost all of the HAM bands including the WARC bands (Rick uses this combination of antennas at his QTH).
My final advice is to be very careful when installing antennas to keep yourself, ladders, antennas, and feedlines away from power lines and take extra care when using ladders and when working at heights above the ground. It is usually best to rent the services and expertise of a bucket truck and operator to install the supports on trees rather than trying to use a ladder or climb yourself. This has the added advantage that proper attachments and pulleys can be easily and properly installed safely. I have used the services of a professional bucket truck and operator several times on projects like these and I have never been sorry about the modest cost involved.
– Fred (AB1OC)
