Month: October 2013
Just want to make a quick post letting everyone that’s reading this know about some upcoming events in the Atlanta area in the next couple of months.
From the website:
The third annual Atlanta Mini Maker Faire is scheduled for Saturday, October 26, 2013 at Georgia Tech from 10am to 5pm. Featuring both established and emerging local “Makers,” the Atlanta Mini Maker Faire is a free family-friendly celebration featuring speakers, workshops, and exhibits on topics such as robotics, green tech, electric vehicles, vintage computing, 3D printing, textile arts, home fabrication, and much more! Get your TICKETS here https://atlantamakerfaire.eventbrite.com/
The Alford Memorial Radio Club’s Stone Mountain Hamfest is being held on November 2 & 3, 2013 at the Gwinnett County Fairgrounds located at 2405 Sugarloaf Parkway, Lawrenceville, GA.
Prizes and announcements will be made on 100.9 FM and the event’s PA system. The event’s talk-in frequency is 146.760 (-) MHz PL 107.2 Hz and a backup frequency of 145.450 (-) MHz and no PL tone.
The North Fulton Amateur Radio League and the Southeastern DX Club will be hosting the 2013 HamJam on November 9, 2013 at the Metropolitan Club, 5895 Windward Parkway, Alpharetta, GA.
On-site questions may be asked on the 2 meter calling frequency of 146.520 MHz.
The event’s talk-in frequencies are:
- 145.47 (-) MHz PL 100.0 Hz
- 224.620 (-) PL 100.0 Hz
- 444.475 (+) PL 100.0 Hz
- 927.0125 (-) PL 146.2 Hz
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.
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.
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.
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.
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!
After the previous post, I continued to work on the antenna configuration some more. The easiest and quickest improvement that could be made was to add more radial elements to the ground plane. After straightening, terminating, and heat shrinking four more 19.5″ 12 AWG wires, it was ready to go. In the first photograph, you can see just the simple antenna assembly and tear down process requires only a screwdriver and a pair of needle nose pliers.
The antenna is great, but I think my radio is a dud. I’ve got a camouflage Tonfa UV-985 handheld radio inbound from eBay, and it’s advertised 8W output is 3W more than the Baofeng. I’ve heard a pretty convincing review from another amateur operator in the local area for the Tonfa, and his expertise is at a level that I’m sufficiently confident in his review being informed and impartial.
Not all of my efforts at making antennas have proved fruitful. Here’s a 5/8 wave ground plane I made using similar construction techniques to the quarter wave models:
The signal quality from the antenna was great! However, it wasn’t structurally sound and wouldn’t hold up its own weight. I thought using a plastic wire conduit, some silicone caulk, epoxy, and heat shrink would be enough to secure it to the base, but it wasn’t. This design also lacks a loading coil at the antenna base to match the impedance with the feed line largely because I didn’t understand how loading coils worked until post-mortem research. I’m curious to try it again using copper piping, but that will have to wait for a while.
I’m going to change directions for the next antenna, and I’m considering stacking 3x quarter wave antennas together in a collinear array antenna with quarter wave matching stubs between the elements. Theoretically, this should provide higher gain over a 5/8 wave antenna in roughly the same amount of space, and real world signal losses shouldn’t detract from this too much. I probably won’t have the chance to start that project for a little while. October is a busy month for our family schedule, and the weekends are fully booked for a few weeks.
Picked up some supplies for the latest construction. Thus far, this design outperforms all others I’ve tried by a considerable margin. The bulk of the design relies on a SO-239 UHF socket adapter used for the antenna body, jacketed 12 gauge solid core house wire for the antenna elements, crimp-on eye terminals, some machine screws, and a bunch of PVC pipe and fittings. Heat shrink tubing, epoxy, and more heat shrink are used to complete the finish for the work.
If the opportunity is present, I intend to make a similar 5/8 wave model using a similar construction method for comparison prior to deciding upon what gets mounted to the exterior of my QTH.
I’ve recently picked up and made some new gear for my rig. Still shopping around for a higher powered radio, but that can wait until the upcoming holiday season. Let’s go ahead and take a look at the new kit.
ExpertPower 14.5″ 2M/70CM Dual Band SMA-Female Antenna
This is a pretty solid upgrade to the stock antenna for the radio. I’m able to get clearer reception over the stock antenna, and I can hit the closest repeaters with a decent signal quality report. It’s a 1/4 wave monopole rubber duck with a floating ground plane, so it doesn’t perform as well sitting on a desk as it does in your hand. Putting a small piece of metal underneath the radio seems to improve the quality without requiring me to hold the thing the whole time.
Homebrew Single-Band 2M Slim-Jim
Dual band antennas definitely seem to be all the rage, but I’m also interested in antennas that will give me solid performance on the bands I use most often. I picked up some air-core twin lead 300 ohm antenna line, some RG8/X 50 ohm feed line, and lots of fittings. The Slim-Jim is an improvement on the traditional J-Pole antenna, but also extends the primary radiating antenna element an additional 1/2 wave folded over where the traditional J-Pole simply ends.
I was getting decent readings from the SWR meter with this antenna design with only a ferrite bead balun at the antenna feedpoint, but something in the back of my head was telling me that I needed to add a balun to match the feed line impedance with the antenna, so I did! It’s covered in heat shrink in the photos, but the balun is a cheap ferrite core wrapped in a 4:1 Guanella winding with small gage wire.
After everything was put together, I whipped up a holder and stand from 3/4″ PVC piping and joints, and it works pretty well. I can’t fit the balun through the pipe, and I’m going to need to upgrade that part to 1″ PVC, but atleast the recipe works and functions better than the 14.5″ rubber duck!
I’m using a SMA-female to SO-239 socket pigtail to connect the handy talkie to the antenna, and I suspect that I’m getting significant insertion loss from that. I have some similar fixtures that are a single component, and I believe that their arrival will further improve my reception. It’s still the best antenna I’ve tested for 2M operation, and I’m able to talk clearly on repeaters that wouldn’t even open their squelch for me before. I can break it down for mobile operation, but it’s not as convenient for that purpose as the rubber duck antennas.
I’ve got some designs I’m considering for making a 1/4 wave ground plane antenna for 2 meters. Some designs incorporate a second antenna element to make it resonant for 70 centimeters, but I’ll wait to bring that part once I’ve got the recipe down for the 2 meter single band version.
I would be a flat out liar if I claimed that I did all of this on my own in a vacuum. I scoured the internet for sources on antenna construction, baluns, and matching antenna impedance to the feed line. Some sources are better than others, but they’ve all been helpful. Here’s some that helped me out with this particular project:
- DU1ANV’s Slim-Jim Antenna Instructions
- HamUniverse’s 2M 300 Ohm Slim Jim Write Up
- KF3G’s 300 Ohm Twin Lead Slim Jim Write Up
- VK5AJL’s “Why Buy Baluns – Make Your Own” Page
- KB1LQC’s “How to Build a 4:1 Current Balun” Page