Category Archives: Antennas

Package Pending

shopping-cart-blur-hiI have some tap and dies on order that I need to finish the 40 meter vertical antenna. I also have some parts  in transit that I need to get started on the antenna tuner which is the next project on deck. As well as the project parts I ordered a couple of items for stock.

One acquisition I have been needing is an LC meter to test inductors and capacitors.The one I ordered measures inductance (L), capacitance (C), resistance (R), and it also checks transistors. A very handy piece of equipment. I have several meters, digital and analog, nearly all measure resistance and voltage, a couple can check transistors, and one can test capacitance in a very limited range.

Since I am planning on making my own air dielectric capacitors, and a variety of inductors and transformers, having a wide scale LC meter will make this work much easier. It will also be a lot of help at flea markets and garage sales to check out components that I am interested in.

With all of this in transit I have some time to get some administrative stuff done. The main thing is to plan out the next few projects. The basic 40 meter direct conversion receiver is done, the antenna is almost done, and the antenna tuner is next with most of the parts enroute, so it makes sense to build a transmitter for 40 meters, I am leaning towards a CW/SSB transmitter.

One of the reasons I want to build CW/SSB is that it will add several other digital modes as well. Many of the digies can be connected straight throught the audio in/out ports on a computer or a handheld device. Leaving only the need to provide a key  or key signal to switch between the receiver and transmitter which could be done manualy or by serial connection to a RT swiching circuit in the radio.

It sounds a lot more complicated that it really is. With a little planning and some experimentation setting up a cable with a couple of connecters on each end will do the job nicely.

I will need to add a couple of circuits to the receiver at some point in the near future as well. An second stage audio amplifier is a must, and a switchable audio filters with bandwidths for CW, SSB, and something in the middle for digi, between first and second stage audio amplification. Neither of these should be all that dificult.

Once I get the 40 meter station all put together I will start work on building another station in another band. By this time I will have figured out a lot of the kinks and bugs and beable to build the second station much more efficiently.

At this point I’m not sure what the next band will be. There are 16 amateur bands currently with the potential of two more that I can gain access to under an experimental license so it is wide open. Each band presents new challenges, ether in technique or materials.

VHF and UHF present strictor tolerances and microwave (UHF-SHF) presents even more challenges. Most bands in HF will be about the same requirements as 40 meter since it is about the miiddle of the HF band. MF presents some challenges in radiators (antennas) because the wavelength is so long. LF presents more challenges in power and radiaors, not to mention the need for that experimental licence.

Fortunatly ist’s all about the fun and learning. As long as I am learning new things, honing skills, and having fun it’s all good.

Until next time, 73
~Jon KK6GXG

More 40 Meter Antenna Fun

20150430_155550Ya know that little voice, sounds like Han Solo in the back of your head “I got a bad feeling…” Yah, that one. Listen to it.

If you look at the image of the antenna base you may notice no screws holding the OS-239 in the bottom of the conduit angle. Now I didn’t leave it all up to gravity. I wound cotton twine around the threads a bunch to keep the connector centered in the hole and was hoping that because the epoxy was pretty thick it would hold down the connector.

20150430_163553Not exactly what I had hopped for. The string did act as a great fiber reinforcement to the epoxy though. Took me the better part of an hour to dig it all out and clear the threads this morning. I know things had gone wrong last night when I did the pour. Thats when I took this picture.

20150430_163541I figured trying to get the epoxy out of the conduit, off all of the components and try again would consume more time than just cleaning the mostly set up epoxy in the morning. Not to mention use up twice as much of a valuable resource. I was right on that one.

I had hoped to use a polyester resin but the can I had was older than I thought so I ended up using some West Systems T-88 structural epoxy, which was also a bit on the stale side so it was very thick. I had hoped that the thickness would be my saving grace on the SO-239. I had also hoped that a lot of the epoxy would filter down the PVC pipe with the antenna but not much of that happened either.

20150501_131622All in all things didn’t work out so bad. After some scaping, thread chasing, cutting and sanding a little gouging as well unfortunatly I managed to come out with a servicable antenna base and connector that is permanently sealed.

20150501_131150I double checked the connector with some feed cabling and all is well with that too. It won’t win any beauty contests and I’m okay with that. As long as it functions well and gives me a good match, that’s all that counts. I won’t be able to test it out until I get the last bits of the antenna finished.

If you look at the image at the top of the post you will see the steel whip is the same diameter as the fiberglass rod. I found some eighth inch bar stock in my materials along with a smaller brass rod so I shifted the plan slightly. I thought the whip should be of a diameter closer to the copper magnet wire of the antenna so the change made sense.

20150501_131901With the last few pieces cut all I need to do is drill, tap, and thread the antenna together then attach the wire to the spike and I can start finding resonance.

I should have the tap and die in the next few days so I should have a working, if not finished, antenna by the end of next week. This project seems to be taking a really long time to complete, and in a way it is. But I decided not to rush things along wouldn’t know it from the goo leak. I also have been doing a lot of day job stuff along the way so time has been divided.

That’s all for now, 73,
~Jon KK6GXG

40 Meter Antenna: Thought Process

I picked up some hardware to connect the antenna bits together into one cohesive unit. Sometimes with hardware you have to just go to the store and look around for solutions to a specific problem or situation.

20150426_122414With this project I wanted to keep things as simple as possible and use off-the-shelf materials that are easily found and relatively cheap. One of the pieces I wanted was a simple piece of hardware I have seen many times. I have even bought it and used it, a three or four-inch long nut.  We used to use them for connecting CB antennas to rigid mounts with a nylon spacer block on the bottom and a bolt. The same basic format used to connect the spring mount base for mobile use. The intended use in this project is to connect the steel spike at the top of the antenna to the fiberglass body.

I remember buying these at Orchards Supply and Ace Hardware. I never had a problem finding one back in the 80s. Yesterday I went to OSH and Home Depot and the employees looked at me like I was from mars. They had these little 1-1.5 inch versions for connecting all-thread, which is what I am looking for, just longer. No clue. Nothing registered on their faces, even with the smaller version in my hand.

20150426_122018Anyway, the next closest thing was turnbuckle bodies. The “solid” bodies were aluminum and the open body type looked like nickel plate and galvanized. I ended up buying an open body style, but it really brought about several issues. First and foremost are the mechanical issues. The contact points on both ends are fairly small, less than half an inch. Even with the fiberglass rod and the steel spike screwed down all the way and touching there is still only a half inch of contact on either end.  These things are intended for stresses in tension not in bending which s what they will be exposed to in this application.

The next issue is the left-hand thread of one end of the turnbuckle. I was willing to deal with this I even started looking for a LH die to thread the fiberglass and this is where I decided to take a step back, reevaluate, and take stock of my options.

20150426_121813At this point the base end has been worked out. The right-angle conduit box is the base and will have 12 inches of half-inch PVC conduit inserted in the port that is parallel to the box. The wound fiberglass rod will be inserted through the PVC pipe into the base. I will cut off all but an eight-inch of the other port which will be the outside housing of the SO-239 which will be inserted from the inside of the box.

Once the antenna coil is soldered to the SO-239 on the inside of the box I will fill the box and the PVC pipe with polyester resin making the base a single solid weatherproof piece. The reason for the PVC pipe being 12 inches long  is to provide a solid place for mounting standoffs to be attached. All done with off the shelf hardware and materials with only one minor modification and no special tools.

Now back to the top end and mounting the steel spike to the fiberglass rod. The most direct method is using the all-thread nut I originally wanted to use. Since it is not available, and a sufficient replacement in size, complexity, and structural strength does not appear to be an off the shelf item, at least around here, I guess I need to make one.

I thought of welding nuts together and other welded configurations but they all require more work than what is really the simplest solution. Drill a piece of half-inch bar stock and tap it for 5/16″ 18 threads per inch. I already picked up the die, now I just need the tap and drill.

This solution does require a couple of tools, tap and die along with their respective handles, the right size drill (an F), and a little machining. This operation isn’t really a big deal. If you have a bench top drill press it will make things easier, but it can be done by hand with a bench vice.

The remaining decision is material for the threaded block. I know I have aluminum and I think I have both steel and brass that are the right size, or at least useable.  I am leaning towards the steel or brass. Aluminum and steel don’t play well together when there is the potential for moisture penetration between the surfaces making galvanic corrosion an issue as well as heat dissipation and mechanical contact issues.

More to come on this subject soon.

73,
~Jon KK6GXG

40 Meter Antenna

With the direct conversion receiver now working and tuned into the 40 meter band, it’s time to get to work on a better choice of antenna. The dipole would be great if it were in the proper environment, but this indoor, RF noisy environment is not conducive to picking up much.

Since tuning the receiver to the band I have been picking up both voice and cw transmissions but they are deep in the band noise. The other issue is portability. While the dipole can be pulled down and packed up for field use, it won’t work well in a mobile environment and would be a chore at home to pull down and put back up. So a whip makes the most sense for now. If the whip works at home I can wind up the dipole and keep it in the ready for field use.

Right now my focus is on getting the receiver, antenna, and any needed matching equipment in place. Once that is all together I can turn my attention to filters, amplifiers, and a transmitter.

Scan from the 1975 ARRL Handbook, page 606.
Scan from the 1975 ARRL Handbook, page 606.

The antenna is a helically wound vertical that I mentioned in a previous post All Aboard the Project Train. I ordered a six foot fiberglass safety flag whip for the core and a fresh 1.5 pound spool of 14 AWG copper magnet wire to get the project going.

Yesterday I started the antenna construction by unrolling the 66.5 feet of copper wire and marking it every five feet, mostly so I didn’t lose my count. After dinner I started winding the coil onto the fiberglass in a tight coil. The picture in the header for this post is the fiberglass with about 30 feet wound on.

20150422_093128
66.5′ of 14 AWG copper wound onto a6′ x 3/8″ fiberglass rod

After winding the rest of the wire onto the fiberglass I threaded a dentists tool in between the wire wraps up the full length of the rod to create the uniform spacing for the coil.

On reflection at this point I think I might have opted for an 8 or 10 foot rod. For most applications it might be a better choice but neither would fit well indoors so 6 foot it is. I may build another antenna like this if it works well and try different lengths and diameters for different applications. A 10 foot whip would be better with a 1/2″ core and any longer would need 3/4″ or 1″ to remain stable unless it were placed inside a tube and filled with epoxy resin, another option. I haven’t tested any of these, I’m just spitballing with the structural integrity issue and weather resistance.

20150421_220832Now that the coil is done, the most difficult and time consuming part I think, it is time to move on to the spike and the base.

The plan for the spike is to pick up a small piece of 3/8″ copper tubing about 4″ long and use a coax crimping tool to mechanically center and attach a 1/4″ steel rod to about 2″ then sweat solder it together. After the spike is properly affixed, scoot the coil up a bit and solder the copper wire to the tube, add some epoxy inside the tube and scoot it back onto the fiberglass rod. This should give plenty of mechanical stability to both the spike and the rod as well as a good electrical contact. To help prevent galvanic corrosion I will coat the steel/copper interface with a few coats of lacquer.

The base is where I am going to have to think some more. The diagram calls for a variable inductor at the base of the antenna. I don’t think I will need this because I am planning on using an adapted Z-Match antenna tuning unit from chapter 23 of QRP Basics but that is for the next project.

OLYMPUS DIGITAL CAMERAIn the mean time I am thinking about using a PVC/ABS 90º conduit fitting with an access panel, cutting off and sealing up the right angle (on the bottom of the image), inserting the bottom of the antenna with the wire sticking up out of the box a little and filling the cavity with epoxy resin, leaving enough room to install an exterior lug fitting to attach the wire to on the inside.  For mechanical stability and to provide a secure mounting point I was thinking about using 6″ of conduit around the antenna and filling that with epoxy resin as well.

I hope to get the spike done this week and the base over the weekend. While out and about getting the final parts for the antenna I will be hitting HSC for the parts for the Z-Match. Another busy week for radio. 🙂

73,
~Jon KK6GXG