Category Archives: Antennas

630m WSPR

Cliff, N5CEY, has been listening to 630m WSPR stations over the past few days and has been consistently picking up three or four stations a night with his antenna system. I thought I would try the same using just the mini-whip antenna and the SDRplay receiver. The mini-whip has been fairly decent on the lower bands. I cranked up HDSDR and when I tuned to the WSPR frequency of 474.2 kHz and found a huge amount of inter-modulation products from local broadcast stations. I tried lowering the gain but they didn’t go away. Looks like I will need a low pass filter or an attenuator.

I then switched to using the SDRuno software that goes along with the SDRplay. It has some filtering features that I thought would be useful to try. The waterfall looked a lot quieter with this software for some reason and after piping the output to WSJT-X I was able to decode 630m WSPR spots from three stations overnight. This compares favorable to what N5CEY saw over the same period.

I will be playing with this some more to see if I can further optimize the receive.

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Practical Application of Soil Measurement Data

Anyone interested in ground radials, ground mounted verticals and even elevated radial verticals should visit Larry Severns, N6LF, website. he has done extenstive research om the subject and has published his results in QST and QEX with many of these articles available on the website. His article ” Experimental Determination of Ground System Performance for HF Verticals Part 4 How Many Radials Does My Vertical Really Need?” was originally published in QEX May/June 2009 edition. The following graph was taked from this paper:

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This graph shows the change of signal improvement on a 1/4 wave vertical with 1/4 wave ground radials under different ground conditions. The impact of this graph is that when the ground is “good”, adding more radials results in small signal improvement vs when using a “poor” ground. I can expect a .2dB improvement if I double my radials from 8 to 16. If I double again to 32 radials my signal improvement would be only around .5dB.

There is a real economic benefit to having good soil as in general fewer radials are needed because the ground losses are less than when over poor soil.

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.

 

Measuring Ground Properties at the QTH

Rudy Severns, N6LF, published a paper entitled “Measurement of Soil Electrical Parameters at HF” where he shows several methods of measuring the electrical properties of soil. I built an OWL probe using his directions made from two parallel 1/2″ aluminum rods spaced 4″ apart and 11″ long.

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Once assembled I measured the capacitance of the probe with the L/C capacitance meter which measured it to be 6.16 pF. I inserted the probe in the ground around my vertical antenna then connected the RigExpert AA-230 Zoom and measured impedance at several frequency points in the HF bands. The Resistance and Reactance are used to calculate the soil conductivity and Er values. Here is a graph of the results:

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The data collected at this one point confirms that the soil in South Texas is quite good in terms of conductivity and Er. I will use these values when modeling antennas with EZNEC. This was the initial test and I will likely try some other areas of the backyard and see how much it varies and whether the data is consistent

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.

A 20m Vertical Beam

JP1QEC developed a portable 20m vertical beam he calls the “Garden Beam Antenna“. I built one this afternoon and have it pointed towards Europe. Construction is stratightfoward. I used a fishing pole to first make a 20m 1/4 wave vertical. It has two ground radials that are about 18 feet long. A third radial extends 18.7 feet from the driven element in the direction opposite where you want the main energy to go. This is connected to two more 18 ft radials and the vertical reflector element also mounted on a fishing pole. I ended up with a very flat SWR of 1.6 across the entire 20m band. I suspect that there needs to be some tweaking to optimize the pattern but I am seeing some directionality based on signal reports from making some JT-65 contacts. The beam is pointed on a bearing of about 40°. I get strong reports from stations in the northeast while stations on the west coast are copying my signals considerably weaker. I made several SSB contacts with most reporting 59+. I’ll be testing the configuration in some more depth over the next few days and comparing with EZNEC results.

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):

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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.