Tag Archives: helically-wound short vertical antenna

Antennas & More

20150507_192446Today was a good antenna day. I finally got the PVC cover on the 40 meter helically-wound antenna I started back in April. I have been using the antenna without the cover as a test antenna next to the bench but it’s time to get it up on the roofline for some actual use.

By “actual use” I am referring to the Beach 40 project that is back in motion now that I have a VXO that pulls more than 1.8 kHz of selectivity. Yay 148 kHz selectivity! Now all I need to do is get the Tx/Rx switching working for the transceiver to be operational.

20140430_131323Another antenna project completed today is the 2 meter twin-lead J-Pole. This one was also waiting for a PVC cover so it could be mounted on a pole. The original design was intended as a portable antenna but the twin-lead J-Pole on any frequency above 50 MHz lends itself well to mounted vertical use, it just needs a housing to keep it in the vertical position.

This little antenna works really well. On numerous occasions I have been unable to ping the local repeaters with my HT with the stock or aftermarket antennas for handhelds. If I attach the twin-lead J-Pole I can actually get out and participate in the nets. With this antenna up in the air at roofline I should have no problems working any of the local repeaters including the packet and Winlink towers.

Speaking of which, I want to get into digital modes once I get the antennas up in the air. I’m not quite up to building a TNC from scratch so I need to save up a hundred and fifty bucks to get digital rolling. Soon…

20151111_145644The other antenna project today was a new-start. When the 2 and 40 meter antennas go up I also plan on attaching a 70 cm half-wave vertical with counterpoise. This one is an experiment. I originally planned on building a 70 cm full-wave twin-lead J-Pole, and I likely still will, but I wanted to see if I could make a vertical with counterpoise that works well. I may even mod this one into a full-wave vertical with half-wave counterpoise radials. Dunno. Like I said, this is an experiment.

Another near-term antenna project, as-of-yet not started, is an aviation band twin-lead J-Pole set up like the 2 meter one. Being a pilot and mechanic, at some point I would like to have either a hangar at a local airport or a small strip at home to work on restorations, so it would make sense to have an AvBand radio in the shop. I have a Vertex Standard (Yaesu) HT for aviation VHF, it just needs an external antenna. I also have a few old radios salvaged from aircraft that would never make it back into an aircraft, but may be suitable for base station operations.

I have a number of other antenna experiment/projects in various configurations, in particular 2 m and 70 cm yagi and/or helical beam antennas suitable for satellite and moon bounce communication. But these are for the future. I also want to build some highly directional antennas for radio orienteering and high-gain narrow-beam antennas for really low power communications.

As for the “More” in the title, once I finish the 40 m transceiver I plan on building a 20 and 10 meter versions. I also have an idea for simple low power beacon transmitters I want to play with. I also want to get set up for QRSS, WSPR, and APRS.

Lots to do. One step at a time.

Till next time, 73,

Marker Generator and more

20150507_190019Picking up where I left off in the last post, I got the drill bits and finished the 40 meter Helically Wound Vertical antenna. I will get a project page up soon.

Now when I say “finished”, what I mean is the antenna is useable. I still need to seal and cover it but I wanted to get it all tuned up first. As far a receiving goes, the vertical is out performing the dipole strung in the house just sitting on the floor leaning up against the wall next the operating station, so it’s looking good.

I need to finish the tuning with a transmitter on it. Since the only transmitter I have for 40 meters is a CW 250mW transmitter I am holding off on that.

20150508_121409In the mean time I put together a Marker Signal Generator. The design takes an 8 MHz crystal and divides the signal down several time ending up with the desired 1 kHz signal with many harmonics to mark out a tuning dial in 1 kHz increments.

20150508_150243It was fun to build and I leaned a little about some ICs I had never used and some of the basics of working with multiple devices in a single package.

When I came to function, I was very disappointed. The oscillator was anything but stable and we very dependant on an extremely stable input voltage. The onboard diode voltage regulations stunk so I tuned down the power supply from 12 volts to the 5 the ICs need.

20150508_153648At this point I was finally able to calm down the oscillator and get close to 1 kHz I was hoping for. A millivolt up or down and the frequency was out. Not a particularly useable device as it sits but it does give me some ideas for using out of band crystals to generate a signal.

As always, this is the whole point, to experiment and learn about RF design by doing, not just reading and modeling on a computer.

The big news, and the reason I missed a post last week is that I have been doing some research on finding my next big build project. The winning design was the Beach 40 by VK3YE. I have been scouring the web looking for a simple phone (voice) transmitter. I was hoping for SSB (Single SideBand) but the Beach 40 DSB (Double SideBand Suppressed Carrier) is simple and straightforward as is.

IMG_20150513_125237Being me, I had to make some modifications to the design and tweak a few things. One of the great things about this design s that it uses discrete components rather than ICs.

At one point Peter (VK3YE) recommends changing the audio amplifier to one that uses the LM386 chip rather than discrete components because the output is rather low. Since one of the main reasons I chose this project was to keep to available discrete components I went out in search of a different audio amp.

Enter Arv Evans K7HKL and his Discrete Component AF Amplifier paper. By the way, at least via email, Arv is a really nice guy. Thanks for the help Arv!

20150513_170104Now with the circuits mostly settled and parts enroute, Digi-Key arrived a day early! 🙂 I sat down tonight and began kitting the parts for each of the transceiver subsections beginning with the Super VXO. I am only installing one crystal set right now but the plan is to set it up for several banks of crystals. I also had some ideas as to using the banks for multiple bands as well as sections of a single band, but that’s for later.

20150513_202942I also kitted the Local Oscillator/Buffer and the Balanced Modulator/Product Detector sections. There are a few bits that will need some refinement, mostly inductors, but these will be addressed as needed.

And speaking of inductors, since I sent back that crappy one I am still in need of one. I will be ordering one tomorrow because I wont get far in this build without one. The goal is to have this radio up and running before Field Day June 27-28.

Look for a project page soon.

Till next time, 73,

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,

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.


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.

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. 🙂


All Aboard the Project Train

Sometimes it is indeed a project train, not just a project; occasionally a train wreck, but it’s early so we’ll hope for the best.

Now that I have built several receivers and a transmitter for 40 meters, I probably should have an antenna that does more than pick up all the RF noise around the shack. The antenna, and I use the word loosely, is nothing more than a dipole of 26 AWG insulated wire strung around the house. While it might work well if the wire was straightened out on a hill top, or even in a backyard, elevated 15 feet or more above ground, in its current incarnation, in a word, it sucks.

Next up on the project block, an antenna, sort of…

I have been looking at several small footprint antenna options like spiral coils that look like those God’s Eye yarn and popsicle stick things you may have made as a kid,  the one in the movies from the 40s when the resistance spy transmitting Nazi secrets and the SS storms in. It looks like a X and has thin wire wound around it.
288And Small Loop antennas that look more like old direction finding antennas on aircraft. And by the way, according to the formulas and general information, for 40 meters, not so small, 10′ diameter.

Now there are lots of variations and tons of experimental configurations to run with, and I do want to play with many of the possible configurations, but I need a stable, small, portable option for the immediate future. Something I could mount on the car, throw up on a pole, or stand up on the back porch, all without much effort. I also need to keep the cost down.

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

Enter the Helically-Wound Short Vertical. I ordered some 14 AWG lacquered copper magnet wire and a 72″ long 5/8″ diameter fiberglass rod, I need to learn to make these so I also ordered a How-To book on making composite fishing rods, and I’m in $20 so far. I have all of the hardware items including the 12″ spike for the top. What I don’t have is the variable inductor, or a tuner.

Whooooo Whooooo! Here comes the train.

RollspuleLets start with the one I haven’t done any research on yet, the variable inductor. The mechanics are fairly simple, rotate the coil and the follower moves up and down the coil creating a tap point. As long as the coil is perfectly cylindrical, the follower makes good contact, and smoothly moves down its axis rod, no sweat. he he he, no sweat I only need the one variable inductor according to the diagram so I really need to find out what value I need. I already have several small value iron-core variable inductors so I may not need to make this one, but if I do, it will be a homebrew. These things are a high-dollar item otherwise.

Moving on to the antenna matching unit. I have plans for one that is fairly simple and straightforward, I even have most of the parts on hand. What I don’t have is the variable capacitors. Sensing a theme here? Variable…

cav-167-205-71_lgBA funny coinky-dink on capacitors; while I was doing research on the Small Loop antennas I came across several websites that went into some lengthy discussions on making variable caps. Turns out, they aren’t that hard to make, I even have nearly all of the materials to make several. Not only are they fairly easy to make, but the formulas for calculating the capacitance based on the area of the plates, number of plates, and the distance between the plates is also fairly straight forward.

So lets see where we are now…
I have three receiver and one transmitter for 40 meters. There is an antenna for them, but it sucks particularly in this location. My next project is to build another transmitter, But I will need a better antenna first…

  1. Antenna
  2. Resonator for antenna (variable inductor)
  3. Antenna tuner
  4. Variable capacitors for the tuner

Now, after these are done I can move on to the new transmitter. As a side note, with the next transmitter project I wanted to pump up the power all the way to a couple of watts, not just miliwatting it. I also want to include SSB (Single SideBand, voice) as well as CW so I can incorporate digital modes into the shack. For all of this the antenna really needs to be better than what I am using.

That’s all for now, 73,