Improved 1/4 Wave & 5/8 Wave Antennas, or Perseverance Pays Off

Posted on Updated on

We’re back again, and I believe I’ve made significant improvements to my rig.  Still running the same rig (hopefully the new transceiver comes in soon), but I’ve improved my construction technique for attaching the antenna’s SO-239 socket to the structure.  Instead of relying on the connector threading to secure the antenna to the PVC caps, I’ve shifted to installing the socket into a PVC reducer to provide physical support to a radome over the central radiating element of my vertical antennas.  It’s been a huge improvement and has made breakdown and assembly of the kit much easier.

Improved 1/4 Wave Vertical With PVC Radome Breakdown
Improved 1/4 Wave Vertical With PVC Radome Breakdown

I’ve also had some SMA Female to SO-239 adapters come in that are an improvement over the RG-58 pigtail I’ve been operating with, and they’ve eliminated the weight of the socket from swinging around like a miniature morningstar.  I immediately recognized the physical strain they were applying to the electrical connections, so I cut a thing 5mm ring of 1/2″ PVC piping with a neoprene washer to add some structural support to that component.  Additionally, the connector appears to reduce the insertion loss into the feedline from mating the RG-58 to the mini RG-8 away from the ground rail of the radio, but I don’t have the equipment necessary to give a solid number to the reduced attenuation.

Female SMA to SO-239 With PVC Ring and Neoprene Washer Strain Relief Breakdown
Female SMA to SO-239 With PVC Ring and Neoprene Washer Strain Relief Breakdown
Assembled 1/4 Wave Vertical with Radome and Strain Relieved Antenna Adapter
Assembled 1/4 Wave Vertical with Radome and Strain Relieved Antenna Adapter

After realizing the improvements to the design of the antennas with the quarter wave, I’ve once again taken a swing at constructing a 5/8 wave vertical.  Previously, I’ve had success with the electrical quality of the antennas, but lacked a decent structural design.  The PVC reducers fix that, and I’ve also designed in a 9 3/4″ long loading coil to electrically lengthen the 5/8 vertical to 3/4 for matching impedance with the 50 ohm mini RG-8 I’m working with.

5/8 Wave Vertical With Radome
5/8 Wave Vertical With Radome

Unfortunately, the coil locks the lower PVC section into place, but I can still remove the top section for trimming the antenna to the resonant frequency.  I’m using an analog MFJ-842 VHF/UHF standing wave ratio (SWR) meter to help me with this crucial step, and I cut the antenna long with the expectation of shortening it to tune.  I freaked out momentarily on the initial test with an SWR at about 3-2.5, but I quickly realized my mistake of not attaching the ground plane radials.  I actually had to snip off about 2-3 inches more of wire than I expected to get the antenna from an initial SWR of about 1.8-1.6 down to one much closer to 1.1-1.2.  My radio outputs max at 5W, but the meter is calibrated for a reading at 10W, so I’m playing with a little bit of guesswork until I get a higher powered transceiver.

5/8 Wave Vertical SWR on 144.000 MHz
5/8 Wave Vertical SWR on 144.000 MHz
5/8 Wave Vertical SWR on 148.000 MHz
5/8 Wave Vertical SWR on 148.000 MHz

I’m not the best of photographers, nor is my camera the best for macro mode shots, but you can see that the needle representing reflected power barely raises up.  It makes it hard to get a precise reading from the device, though, but it was an incredible improvement over the initial SWR test prior to cutting to a resonant length.  The Baofeng UV-5R is advertised as a 4W transceiver, but I can clearly see it outputting a full 5W on the SWR meter with a well matched antenna.

I’ve got much better signal reports with the 5/8 wave antenna from my local repeater contacts, and I’m able to hear them from a room I typically cannot even key up the repeater from.  The Atlanta area tends to have lots of hills and terrain features, and my home location is somewhat in an elevation bowl.  5/8 wave antennas have a narrower vertical radiation lobes than 1/4 wave, but I’m making up for it with the higher takeoff angle.  It would be more practical to make a repeater antenna with something covering a wider area, but this will be an excellent antenna for mounting to the structure of my base station.

My plans for the base station antenna system are slightly different from the portable antenna designs I’ve recently been focusing on.  I intend to create this antenna to be fixed and permanent, so I’ll be working with copper piping instead of thick gauge copper wire.  I want to use copper tubing for the ground plane radials, and copper screws (if I can find them) for attaching the socket to the mast.  I’ll solder as much of the hardware together as I can, and then I’ll give it a few coats of either black or grey spray paint.  I’ll depart from cheaping out with mini RG-8 in favor of LMR-400 for the feedline, and I’m considering better connectors than PL-259/SO-239 to further reduce the feedline losses.  Hopefully I’ll be able to get some solid range out of this dirt cheap handy talkie this weekend while we’re out camping!

About these ads

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s