Antenna – Page 3 – AB4UG Radioblog

A 6m dipole

Built myself a 6m dipole using a dipole center and some of the hamfest wire I picked up back in February. As it’s also Towel Day, I had mine handy just in case.

I wanted my antenna to be resonant at 51 MHz. Using l = 149.35/f ¹ gave me a length of 2.96m, so I cut a 3m length of wire and then cut that in half. I soldered some stranded wire to one end of each wire to connect to the dipole center and attached a couple of ceramic insulators to the end. One end got tied off against the house and the other end to my PVC mast propped up against a ladder.

The first look with my antenna analyzer showed the antenna resonating around 49.3 MHz with an SWR of 1.0 (wires a bit on the long side). A bit of math (49.3MHz/51MHz = 0.97) told me the antenna needed to be 2.9m long (3.0 * 0.97) so I trimmed 5 cm off each end and got 1.0 SWR right at 51 MHz.

With the dipole connected to the radio, the receive is definitely louder than the ZS6BKW on 6m. I wasn’t able to pick up any other stations, but there was a lot of electronic noise. In the fldigi waterfall, there were lots of periodically spaced vertical lines all across the band. I’ll have to give a listen later when it cools down a bit and people turn off their AC units. Maybe it’ll get better then.

At 2.9m long, it’s small enough to be very easily portable. I’ll need to get a much shorter length of coax to use with it to minimize losses (it’s connected to the radio using about 23m of coax) and something to hold it up in the air. Could be neat to carry this around and break it out when a 6m opening pops up.

1. Take l = 490/f, which gives you the length in feet when f is in MHz, and multiply by 0.3048 to convert to meters. Metric is how I roll.

10m Moxon in the air

Got the 10m Moxon up in the air on my PVC mast. Using both 10 foot sections of the mast proved to be a little too cumbersome for just myself to handle, so settled for using one 10 foot section and propped it up against a ladder for support. This gets the Moxon 4.15m (13.6 feet) up in the air. Not quite as high as I wanted, but for testing purposes, it will do.

Fiddled with the antenna element lengths and was able to get the SWR as low as 2.5-2.6 across the band, which is pretty close to the limit of what the tuner in the radio will match. Should be able to get it lower but I’m sure the ladder is messing things up some.

In any case, the antenna is up in the air and connected to the radio. Receive seems to be working pretty well. Loud stations come in louder, and the fainter stations come in just a little bit louder. I could definitely see a difference switching between the Moxon and the dipole while watching some 10m PSK.

Haven’t tried transmitting on the antenna yet. I’d like to see if I can get it a little higher and tune it so that the SWR a little lower.

Working with the shortened version of the mast seemed to work out pretty well, so I think as a platform for antenna experiments, it will do nicely.

Now to work on getting the antenna up higher and installed more permanently.

PVC mast construction

To get the 10m Moxon up in the air, I decided I was going to build a mast. My primary criteria for a mast was being able to lower it easily in case stormy weather rolled through. For now I’m not all that concerned about it being a permanent type installation yet. That will probably come later.

With that in mind, I decided to build the mast using PVC pipe. Off to Lowe’s I went to pick up a couple of 3″ by 10′ sections of PVC, a 1″ by 5′ section that the antenna will mount to, a coupler to join the 3″ sections with and caps for the ends of the pipes.

My original thought was to put the 1″ pipe on top with a reducing coupler, but I couldn’t find any 3″ to 1″ reducers in my earlier scouting trips. After looking around the garage to see what parts I had on hand, I decided to use some 4.5″ bolts and wing nuts to secure the 1″ pipe to the 3″ pipe.

Drilled three holes, but then discovered the lowest hole was too far down the pipe for me to reach. Fortunately it seems secure enough with just the two bolts.

With this I’ll be able to get the Moxon up between 20-23′ up in the air, and maybe even have enough room for another antenna on there too. Getting the whole thing vertical proved to be more challenging than I expected. I think I’m going to need a ladder to get it vertical.

It definitely needs guy lines so getting those positioned will be the next step. For now everything is back in the garage waiting for my next free afternoon.

Dipole centers

Should be able to make a couple of decent dipole antennas with these center insulators

Maybe I’ll take that 10m hamfest antenna and put it on one of these.

10m Moxon assembled

After a few hours of reading instructions, screwing and clamping things into place, then undoing it all and redoing it properly because I didn’t read the instructions thoroughly enough, I got the 10m Moxon antenna assembled. The bent tubes were easy enough to straighten out, and the one tube that had 2cm broken off was still long enough to work with. I managed to lose a hose clamp somewhere along the way, but fortunately I was able to find another one that worked in one of my toolboxes. Ended up with a bunch of extra lock washers too that didn’t seem to be in the parts list in the manual.

Here’s the feed point, which I’ll probably zip tie (or some other tie) onto the beam.

It’s a pretty big antenna, at right around 3.97m (12.4 feet) long. Here it is up against the car for some scale.

Now to figure out how I’m going to get it up into the air…