Tag Archives: Antennas

More on Soil Meaurements

It is extremely easy to take soil electrical data using the RigExpert by running a frequency sweep. This sweep is saved on the meter and then transferred to the PC and exported as an CSV file. This file contains impedance measurements across the sweep range. Add the formula to convert to conductivity and Er and you get the following graph:

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This data was calculated with a Co = 8 pF adjusted after making a few more measurements. The average values per band are as follows:

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The values above can be compared to those given as standard values in EZNEC. I further compared the gain results when using a 40m 1/4 Wave vertical with four ground mounted radials as follows:

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In this case, the model has a 2.27dB difference in measured gain between the average soil case and the measured reading. In practice, using the “Very Good” values will likely be close enough for modeling work here at the QTH.

 

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20m Hamstick for Balcony Operating

I discussed a 20m vertical using a hamstick for balcony operation. I put this together this afternoon and ran some tests. Here is a view of the antenna attached to a lawn chair about four feet off the ground.


The antenna performed well on receive against the 1/4 wave vertical but WSPR results were not to good. No stations heard my signal even up to 5W. Not sure if the band conditions were a factor. The only contact I made was to Costa Rica on SSB so it’s does work! The stinger was adjusted to 36″ and the SWR was below 2:1 across the band.

More on the 20m Vertical Beam

The vertical beam is definitely directional. Unfortunately, I have no way to measure the gain. What I have noticed is that when I run this antenna on JT-65 I see much stronger reports from the direction the beam is pointed to versus the backside. Same goes with WSPR results. The antenna is also receiving well based on yesterdays WSPR challenge results as well.

I did some A/B switching between the beam and the 20m vertical while running JT-65. The beam sees signals coming in from Europe (very weak just above the noise floor). These disappear entirely when switching in the vertical. This could make a very nice antenna for next field day as it is easy to setup and from my QTH would cover much of the US my pointing due north.

Here is a picture of the antenna deployed in my backyard:

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These pictures show how everything is connected:

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At the feedpoint I have the homebrew 1:1 current balun. Each vertical element has two 18 foot radials laying on the ground. The two radial sets are connected by an 18.7″ ft wire. Pretty simple really.

The Hardware Store 40m Magnetic Loop Antenna

A while back, I wrote up and submitted some info to QST antenna design competition on my 40m Magnetic Loop antenna. The contest is over so I am now publishing the write up on this site on the Projects page. The direct link to the file is here.

The write up details the design and construction of both the 40m Loop antenna and its High Voltage capacitor made from Copper tubing. Nearly the entire antenna can be made from parts gathered at your local building supply store. Hope some of you find this Useful!

A Cool Idea for a 20m Hamstick

I found this configuration for a single 20m hamstick antenna which may be a winner for balcony operation at South Padre Island. The hamstick connects to a T connector. One end of the T connector goes to the feed line and the radio. The other end has a shorted 1/4 wave length (corrected for cable VF) of coax as a counterpoise. Here is the configuration (thanks to PD7MAA):

no ground antenna

This assumes the stub is RG-58 with a velocity factor of 0.66. Other coax types simply calulate based on the new velocity factor.

Antenna Experiments Continue

First up is a broadband EFHW using an auto-transformer wound on an FT240-43 Ferrite toroid. I used 18 gauge doorbell wire (had to remove the outer jacket of the wire pair first. The basic wiring looks like this (thanks to PA3HHO):

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What is not shown here is a 150pF capacitor across points A & B. Here is the completed toroid:

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Here I test the matching by connecting a 3.9KOhm resistor across point B & C along with the 150pF capacitor across A & B. Here is the SWR plot:

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SWR is below 2:1 across nearly the entire band 80m to 12m 10m is 5:1 well within range of a tuner. I will mount this in a box with a UHF connector and two banana jacks, One for the antenna wire and the other as a ground connection. Once complete I’ll try first with 40m 1/2 wave wire. That should give me a good match on 40m, 20m, and 15m. The wire will be around 66 ft long.  I should be able to add 80m by adding a loading coil and an additional 2.5m piece of wire. Planning to un the first 10m of wire up the travel mast then bring the rest down as a sloper.

WSPR Data collected from the 20m Hamstick Vertical Dipole

Here is 24 hours of WSPR data collected from the 20m Vertical Dipole:

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There were 114 unique receive spots and 90 unique heard from spots with 1W transmit. This seems low compared to N5Cey’s 20m 1/4 wave vertical which typically receives 180 to 200 unique spots from his QTH near Los Fresnos.

I did some A vs. B tests on SSB yesterday switching between the 1/4 wave vertical and the vertical dipole. This time I used a remote receiver using Websdr.org. I connected to a station in the San Fransisco area and monitored my voice transmissions. In this case the vertical dipole came in about 1 S units stronger. I then switched to a station in New Jersey and the opposite was true!

I am going to do some additional testing on various 20m vertical configurations using WSPR over the next couple of days.

A 20m Vertical Dipole…(I am a glutton for punishment)…

Here in South Texas you hear a lot about the Canicula. July 14 through August 24th is considered to be the hottest part of the year. It’s 94° F here today but when you add the 54% humidity we get a heat index of 106° F. So naturally I choose today to play with a new antenna!

I built a vertical dipole for 20m today using two Workman Hamsticks. I thought this would be fairly easy as I didn’t have to get it too far off the ground. More on that later…

I read that one ham had pretty good luck with the stinger set at 38″ so I set that as a starting point. I set it up vertically on a painters pole with the bottom stinger about a foot off the ground and found the SWR minimum was in the 13.5 Mhz range. I shortend the stingers and the SWR went down to the 13 Mhz range. I played with this for some time until the whole mess collapsed in the breeze. Arrrgh!

I came inside and after re-hydrating played around with the antenna again. Nothing I did seemsed to work in getting it to tune in the 14m band. I got it back to the original configuration and ventured outside again. I set it up as before and the SWR was in the 13.5Mhz range again. This time I guyed the painters pole and sent it up a few feet. The SWR started going down with the minimum frequency going up into the 20m band…Aha! I raised it up so the feed point was about 15 to 16 ft off the ground. This put the end of the stinger at about 8 feet.  Now the SWR response looked good with 2:1 or less across most of the 20m band.

Inside again now I started to tune around and found the SWR swinging again. Suspected Common Mode Currents again so went outside and lowered the antenna to 8 feet, redressed the coax so that it comes out away from the feed point at 90° for about three feet. Now everything is working out fine. I made an SSB contact to Chile and to Guatemala right off.

So here is what I learned today:

  1. It is too hot in South Texas in August to play with antennas…wait till early morning or very late in the afternoon next time.
  2. A vertical dipole needs to be a few feet off the ground to tune properly
  3. It is vitally important that the coax feed line in a vertical dipole come out at at 90° angle for several feet to avoid common mode currents.

Here is a view of the antenna:

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Here is the SWR plot:

20m dipole vert

Will run 1W WSPR for 24 hours and compare data with the 1/4 Wave vertical.

 

 

My Ugly Balun

I built an ugly balun today to try and address the SWR swings I was getting on 20m. It actually went together in about 10 minutes. To build it I used a 4″ PVC pipe coupler as a form. I drilled two small holes to run a tie wrap through to hold the end of the coax in place. I had a 25 foot piece of RG-8X laying around with PL-259 connectors on each end. I wrapped 15 turns around the coupler and then tied it off the same was as the other end. Some long tie wraps then are used to hold the winding securely on the form. I replaced the 1:1 current balun I had been using with this. To match up the coax connectors I used two bulkhead connectors and wrapped with electrical tape (for now). Here’s what the finished balun looks like:

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And here it is installed at the vertical antenna feedpoint:

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The balun seems to help with the SWR issues on 20m but I see some shifts in the overall SWR response. I’ll likely have to tweak that over the next few days.I have some ferrite toroids on the way as well and will try and build a choke with those as well. Signal reports on both 40m and 20m SSB were real good tonight!

 

What’s Better than One 1/4 Wave Vertical? —How About Two?…

Next experiment in vertical HF antennas is trying a 1/4 wave vertical “fan dipole”. The 7.2m fishing rods are a perfect support for up to a 20m wire radiator. I set a length of 3/4″ PVC pipe about a foot away from the existing 40m 1/4 antenna. I also removed the last two section of fishing pole as they are too flimsy and are not needed length to support a 20m wire. I connected this wire to the point where the 40m wire connects and after a bit of tuning had three dips in the SWR. 7 MHz is the main tuned frequency, 14 MHz is the new radiator and 21 MHz is the third harmonic of the main radiator. Here is the SWR plot:

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Here is what is looks like:

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So far this works well as before on 40m and 15m. The performance on 20m looks a little shaky still as I am seeing my SWR swing around a bit when transmitting. This indicates to me that my feed line is picking up RF at that frequency. I’ll be building an Ugly Balun soon to try and clean that up. The antenna hears very well on 20m with very little noise so I f I can solve the SWR issue I should be in good shape.