Back on July 17, 2022, I made a post here about building a DIY Moxon antenna for 6m based on plans in the ARRL book Magic Band Antennas for Ham Radio by Bruce Walker N3JO. It was made of flat aluminum bars instead of round tubing. The problem with it was that the ends drooped significantly, which reduced the directionality.
I expected this, so I used a cross instead of a ‘T’ in the middle of the boom. That let me add a vertical extension of PVC pipe in the middle of the boom. I drilled a hole in the top of a PVC cap, mounted a (stainless steel) eye-bolt in the hole, and put it on top of the extension. (With the mast lying on the ground, of course.) Then I was able to tie paracord from the eye-bolt to each end of the antenna as shown in this picture. I am more concerned about accidents with the lawn mover than stealth in my back yard, so you can see that I used bright safety orange and safety yellow-green paracord for the guy lines. (In fact, my neighbor, also an engineer, commented that this was a good idea, to prevent tripping.)
I used the “Orange Screw” product mentioned here by others to anchor the guy lines to the ground. I also used hose clamps, in addition to the mast’s own clamps, to keep the mast from telescoping inward.
It’s important to remember that the only two knots to use with antennas are:
the taut-line hitch and
the bowline knot.
(To help with pronouncing the later, try to remember that it was named for the front end of a boat, where sailors use it.) These knots were covered in the Tech Night presentations about Field Day.
The ARRL book Magic Band Antennas for Ham Radio by Bruce Walker N3JO has the plans for a 6m Moxon Antenna that I found interesting because, instead of wire or tubing, it uses 3/4″x1/8″ aluminum stock available in hardware stores in 4′ or 8′ lengths. No bending, just drilling! I’ve worked on it bit by bit over the last few months or so, and the CQ VHF contest this weekend gave me the extra push I needed to get it up into the air!
I got 8′ sections of the aluminum stock, but I cut the center of the parasitic element (the longest piece) into 2 pieces of less than 4′ each, in case I want to pack the antenna into a car.
The boom is PVC pipe, and for the spacers between the active element and the parasitic element, I used a 1-1/2″x3/4″ vinyl substitute for wood used for trim, which is also available in hardware stores. I cut it down to 3/4″ wide strips for the insulators between the ends of the elements. Unlike the book, I used the full width to attach the elements to the boom so that the U-bolts could be attached beside, instead of under and through, the elements. (It was not at all clear to me from the book’s drawing — no photographs — how the parasitic element was attached to the boom given the bolt positions as drawn. Also, I may have misunderstood if the author meant 1″ ID or 1″ OD pipe; since it is Pipe, I assumed it was ID.)
I made a coil balun as described in the book, and the UHF connector is mounted on a right-angle piece of plastic cut from an inexpensive outlet box which is a trick suggested in the book.
I put Noalox on the stainless steel nuts and bolts to prevent them from “welding” themselves together and also to protect the aluminum from the stainless steel.
I changed my ideas on how to get it up into the air a couple of times, and today I finally just went and got an MFJ-1911 lightweight fiberglass mast and a set of MFJ-2830X guy rings at our local “candy store.” (I wish there were a ring in the set with an even larger center hole.) I did not extend it to the full 20′ (yet, anyway) because I was concerned that the antenna was too heavy, so it is only about 14′ up in the air now.
I used hose clamps (threaded through a water drain tube, so the clamps don’t cut into the mast) above each exposed joint in the mast to give added protection against the “twist lock” mast unlocking and collapsing into itself. I put another one around the base with loops of paracord through it that I can hold down with tent stakes, in addition to putting the base of the mast against one of the raised garden beds to keep it from slipping. (I’m sorry, I don’t recall which video blogging ham I learned those hose clamp tricks from.)
6m Moxon based on a plan by Bruce Walker N3JO before it was raised up
The 6m Moxon Antenna ended up being tilted slightly (actually, rotated around to be almost upside-down!), but I’ve got some U-bolt saddles on order to fix that. (They’ll be the two pieces of metal besides the aluminum elements that aren’t stainless steel. Unfortunately, I used a smaller size U-bolt than what seems to be the “standard” for antenna masts of about 2″ inside diameter for the U-bolts.) I made an extension that screws in above the vertical piece of PVC pipe through the boom so that I could add support ropes for the insulators far out from the center of the antenna, but I haven’t put it on yet to save weight. (I may replace the mast with a heavier-weight product from MFJ to allow this and to raise it higher.)
6m Moxon based on a plan by Bruce Walker N3JO
As you can see below, the minimum SWR is 1.0 at about 52,140 MHz, not the point in the 6m band where I would like it for FT8, but at least it is in the lower half of the band. (I haven’t thought about how to tune it or if I need to. But I do know that I want to replace the thin coax feeding the antenna now with LMR-400.)
SWR curve hitting 1.0 at about 52,140 MHz
With much-appreciated help from my XYL Merle W1MSI, I was able to get the DIY 6m Moxon Antenna up late this afternoon and try it out before the band closed for the day. The “magic band” did what it does, and I was able to make 27 QSOs on VHF with FT8, from my shack in FN42 (southern New Hampshire) to as far as EL98 (Florida) and EN52 (Wisconsin). So I think the antenna is working pretty well. It is the first beam antenna at my shack.
For a while there, I was happily collecting DXCCs and US states on HF with SSB, but then I discovered FT8, and after that FT4, and now I’ve got grid squares to collect on VHF — so I have even more paper to chase!
Which is best for QRP Antenna Connectors: BNC or RCA? I’ve seen both on the web, so I’m trying to decide which connector to use for a QRP antenna. Maybe you can help me out: Which is the “best” (most common, most useful, works best) for a QRP Antenna Connector: BNC (which stands for “Bayonet Neill-Concelman” according to Wikipedia) or RCA “phono” connectors (they were used for connecting a turntable to an audio amplifier for something like a half a century)?
50 Ω Female BNC Connectors (Photo by W1AKI)
BNC connectors cost more but won’t come loose. RF cables with BNC connectors seem to be more available. What I didn’t realize until recently is that they come in both 75 Ω and 50 Ω types. My picture above seems to be of the 50 Ω type. Wikipedia has a side-by-side picture comparing the two types. The commercial version of the Buddipole uses them.
Female RCA Connectors (Photo by W1AKI)
RCA connectors are inexpensive but can become unplugged. This can be an annoyance if you lose your connection when someone trips over the cable, or it can be a feature in that the antenna won’t get pulled over when someone trips over the cable
(Of course, any cables that are up over the ground, or any guy lines, should be marked with flagging tape — available from any hardware store — to prevent someone from tripping.)
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