Category Archives: Antennas

Don’t Drop the Toroid!

I sat down to start working on the phase transformer for my phased vertical project. I dropped the toroid!

Sigh!

Just ordered a replacement. Hope it arrives before I break for Christmas….

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Using SDR Receivers to Track NOAA Weather Balloons

Found an article by the folks at RTL-SDR that shows how to recieve data from NOAA weather balloons. This look like a fun project and considering the balloons at the NWS Brownsville are launched twice a day just 2 miles from here it could be very doable.

40-20-15m EFHW Round 2 – Update

WSPR results o 40m and 20m WSPR look good with the EFHW. here is 40m during nightime hours:

2017-12-11_9-54-35

And 20m for just a few hours yesterday and so far this morning:

2017-12-11_9-55-11

On 40m there have been 103 unique heard vs 106 heard by (@1/2 W). On 20m, this is 124 unique heard vs. 74 heard by (also @1/2 W). These numbers indicate good overall performance.

I found a great write up on how to build one of these antennas titled “A Shortened Multi-band End-Fed half Wave (EFHW) Antenna for 80-10m” by Steve Nichols, G0KYA.

I am going to do some work on how to best deploy this in the field given my typical situation (i.e. lack of tall trees). this could be a great Field Day antenna.

40-20-15 EFHW Round 2

There were some things bothering me about the EFHW matchbox. I would run a scan using the RigExpert with a 3.9K Ohm resistor from the antenna line across to the ground and sometimes get a good reading and sometimes not. I suspected a poor solder connection or the el cheapo binding posts I was using. Well I am done with the el cheapo binding posts! From now on I am using stainless steel machine screw hardware. I replaced the binding posts with these and the readings settled out.

I made a few other changes for round 2 with this antenna today. First up, I wrapped the end of the RG-58 cable eights times around an FT240-43 core to act as a choke at the feedpoint. I added about six feet of counterpoise. I went back to setting this up a a low inverted V of sorts. The feedpoint is over a tree branch on one end about 6 feet off the ground. The other end is supported by a fishing pole. Unfortunately, this configuration had a huge amount of sag in the middle. I placed another pole in the middle so the apex is up about 16 feet. Not happy with this configuration. I will use a sturdier pole and set this up as a true inverted v next time around. meanwhile, I am running some test in this configuration. SWR was good on 40m and 20m but a bit high on 15m:

efhw

Initial WSPR results on 20m look promising. 1/2W signal is showing a good ratio to received spots. I tried a few SSB contacts but none were closed. I’ll run WSPR on this over night on 40m and 20m and see what the data shows. I’ll then switch to a 10m pole to support the middle of the wire into an inverted V.

One more thought is that I’ll add a 110uH coil to the end of the wire then about 2m more of wire, the idea that it can trap 40m and then act as a loading coil on 80m. I have worked out the coil dims for this using a 1-1/4″ PVC pipe coupler as a coil form. 110uH works out to 52 turns of #20 magnet wire.

40-20-15 EFHW

Here are the 24 hour WSPR results on 40-20-15m receive using band hopping. They appear to be pretty consistent with current band conditions and while not as good as the 1/4 wave vertical it is a very respectable and very portable multi-band antenna.

40m40m

20m20m

15m15m

The SWR plot is as follows:

swr

These antennas are increasingly popular and many quality antennas sell for ~$140. Building your own is very simple and I would estimate my cost to build this would not be greater than $30. This will work out to be a good antenna for portable or field day use. It is not especially sensitive to mounting or orientation.

 

EFHW Broadband Transformer On the Air

Back in late August, I had a post regarding a broadband auto transformer for an EFHW antenna. I finally got around to cutting 66ft of wire (1/2 wave on 40m) and did some basic tests. It is only up about 10 ft and stretched out north-south across the back yard. The RigExpert Zoom showed dips in the 40m, 20m & 15m bands. SWR is below 2:1 across each band. Twenty-five feet of coax forms the counterpoise. Very promising. One SSB contact on 20m yielded a 57 report on this antenna and the 1/4 wave vertical. I am running WSPR now on 40m. Tomorrow I will raise this up to a least 20ft and run some more tests. If I add another 66ft it will be a 1/2 wave on 80m and should get me a match on all bands (except 60m) between 80m and 10m.

Junction Box for Vertical Antenna

Here is a simple junction box I built to simplify setting up a vertical antenna. The hardware is all stainless steel. There is a 1Meg resistor across the feed-point to bleed off any static. This box will replace a coax pigtail. Ground radials connect to one lug and the vertical element to the other. The coax from the ugly balun connects directly to the UHF connector.

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Antenna Cleanup

I took down the ground beam QEC antenna and the 20m quarter wave element that I had connected to my 40m vertical today. I am not really seeing much of a difference on 20m although I need to use the tuner now.

I have some construction projects I need to finish before I make some additional antenna tests. I am building some boxes to clean up vertical antenna setups. I am also working on the phase transformer box for the 20m phased vertical experiments. There are feed lines to prepare for this.

Once I have the vertical feed boxes complete I would like to convert the vertical to an end fed with ground radials. I recall this configuration worked pretty well.

More Test Results of The Ground Beam QEC Antenna

Tried 20m FT-8 early this morning as VOACAP indicated this was the best time for EU contacts on this band. My signals were heard toward the Northeast US but very few were heard in the EU. I made no QSO’s. WSPR results over 24 hours are here:

wspr mapo

This data appears to confirm that this antenna is directional (I have it pointed at a 45° bearing from my QTH)  but the F/B ratio is still relatively poor. The antenna is about the same as the 1/4 wave vertical overall. I must say that my single reports in the forward direction on SSB have been very good. Propagation on 20m is not helping. VOACAP shows the following based on 100W SSB with the receiving antenna based on a dipole at 10m:

prop1prop2

20m has been largely dead after dark. This chart indicates that 20m contacts with this combination of antennas and power will be challenging to the EU.

Overall, The ground beam – QEC antenna is an easy to carry and deploy vertical antenna with just enough directionality to help in some situation. It is well suited to my QTH on filed day as it has a wide enough bandwidth to cover the USA and Canada.

Musings on Vertical Beam Antennas

I have been doing some EZNEC & Propagation studies on various vertical configurations. First off is the Ground Beam QEC antenna. The EZNEC model looks like this:

gbqec

The model indicates (and the performance seems to confirm) that this antenna is directive but the small number of ground radials causes gain to suffer. The main benefit of this antenna over a vertical is that it has some F/B reduction. Running some optimization on this models indicates some improvement by significantly lengthening the reflector. The gain increases slightly but the F/B ratio improves. Unfortunately, the reflector would have to be 7m long for a 20M antenna making deployment difficult using the telescopic fishing poles.

I was thinking about the homebrew Buddistick I built a while back and remembered it exhibited modest forward gain in the direction of the single elevated radial. Here is the model:

buddistick

This antenna is somewhat directional but also has considerable high angle radiation. It would still appear to be a better performer as a beam than either the 1/4 wave vertical or the ground beam QEC antenna. Drawbacks?…not as lightweight.

My final candidate is a 2 element vertical beam. Making a few compromises in mounting I can use the fishing poles to make a full size 1/4 wave vertical on 20m using a single elevated radial. The feed point is only 3 feet off the ground. Here is the model:

2el vert

This can be built in a manner very similar to the ground beam QEC. I just need to figure out how to mount the ends a bit higher. Horizontal space needed is about 16 feet greater than the ground beam QEC. here are the radiation patterns from the model:

pattern

To summarize this chart, the GB-QEC is almost equal to the 1/4 wave vertical in forward direction but with some rear rejection. The 20m Buddistick has greater forward gain, some rear rejection but considerable high angle radiation. This antenna makes a great Field day antenna at my QTH as it can point north and cover most of the USA and Canada. Finally the two element vertical beam provides 3db greater gain then the 1/4 wave vertical with 8db F/B ratio and good low angle radiation.

This info leads me to want to try the 2 element beam next. These parasitic beams are of course fixed in direction. The phased 2 element vertical array has the advantage it will provide some steering.