Tag Archives: eznec

Holiday Project Update

Managed to finish rewiring some of the shack for shorter cable runs and lower RFI. The shorter cables are especially handy on the FT-817ND. I can now neatly accommodate any combination of radio, amp, tuner and SWR meter. It is crazy windy out here today so I will likely wait until next week and setup the Buddistick and run the FT-817ND at 45 watts portable.

The APRS cable project has been de;ayed by the lack of a correct cable for the radio. The correct cable should arrive on Tuesday so I will wrap that project up then.

Been rethinking the 20m-10m portable beam project and am doing some EZNEC modeling. The issues I am looking at revolve around a portable 20m 2 element yagi that I can only raise up to about 20ft versus vertical buddisticks.

Thinking of a 2m Yagi

Looking at the Yagi again for 2m. The Moxon had a predicated gain of about 7.5dBi. This is roughly equivalent to a 2 element Yagi. So to get any improvement I would need to go with a 3 element Yagi. I’ve layed one out and here are the EZNEC predictions:

2015-07-22_12-25-582015-07-22_12-25-43

The compromise here is reduced beam width vs. higher gain. This would give me 12.1dBi of gain vs. the 7.5dBi on the Moxon.My guess is that at 5w I will be heard simplex in Weslaco and improve reception from the upper valley. I will probably put this on hold as I now have the parts I need to start my HF magnetic loop antenna project. I am also hoping to get an FT-857D soon that would give me 50W of VHF capability.

SImplex Testing of the 2m Moxon

Setup the 2m Moxon on a painters pole late afternoon yesterday and checked into the local daily ragchewers net. Was able to hear the repeater traffic in Brownsville, Harlingen and La Feria at full quieting. South Padre Island was readable but scratchy. Could not hear the Edinburg or Raymonsville repeaters at all. W3OQ in Olimto helped me do some testing. I was able to work the La Feria repeater with no problems with full quieting reported on the local repeater node.

Photo Jul 21, 7 24 24 PMPhoto Jul 21, 7 24 56 PM

On simplex I heard stations from Mcallen/Mission and Weslaco for the first time. The Weslaco station could hear me only once. Stations in the upper valley were fading in and out but could not hear me. W3OE was reporting hearing stations near Corpus Christi and received a text message that he had been hear near Refugio.

So to summarize, the 2m Moxon does show an improvement as predicted by EZNEC. At 5W this is not enough to be heard widely through region on simplex but does give me access to a number of other local repeaters. Note that many of the simplex stations I was trying to work are on 50W and have antennas mounted up around 40ft.

More on a directional VHF antenna

Now thinking that a better choice over a Yagi for 2m is a Moxon. The Moxon has a few really positive attributes:

  • Reduced size – folded elements
  • 2 elements have approximately the same gain as a 3 element Yagi
  • Large Beam width and Front to Back ratio
  • Easy and cheap to build

For 2m the Moxon rectangle works out to about 29″x11″. Here are some EZNEC predications for such an antenna realized with #8 copper wire:

2015-06-30_12-52-332015-06-30_12-52-55

I am going to try an build this by making a frame out of 1/2″ PVC and then putting the #8 wire around it and holding it in place with zip ties. This should be a fun and inexpensive experiment for 2m

VHF Yagi Ideas for Simplex Work

Some local hams have been experimenting with VHF simplex for communicating up and down the valley. The guy who usually leads these experiments is located in Brownsville and has his VHF vertical mounted on a 40 foot tower. He is able to communicate with other hams up and down the valley depending on the other hams configuration. I can communicate easily with him from my home QTH but I am deaf to all but one other local ham on simplex.

My VHF station is spartan at best. I use a 4W Baofeng handy talkie connected to a discone antenna that is up about 10 feet. I get no gain from the discone. This setup works real well for hitting the local repeater and for limited local simplex. I started thinking about the geographic location in respect to other stations in the valley and plotted the following map:

2015-06-30_7-16-07

My QTH in Brownsville is in the lower right hand side of the map. The Rio Grande River is the US-Mexico border and the Gulf of Mexico is to the East. To cover the valley I only need a Beam width of about 126°. I started thinking about building a 2 element yagi vertically oriented and came up with the following azimuth pattern using EZNEC:

2015-06-30_8-51-10

This antenna would give me a 133° beam width and a gain of 7.5dB over what I have now. My only concern is the rather low take off angle of the main lobe. Clearly the higher the better for this antenna but it looks like it would be a good starting point for experiments. Should be fairly simple to build from PVC and aluminum tubing. Will post more as I progress on actually building this.

Portable Antenna Analysis Roundup

Portable Antenna Analysis

The link above is to a file containing a EZNEC analysis of various antenna types I am looking at for portable use. These are mainly based on the Homebrew Buddipole and Buddistick designs that I have been working on with an emphasis of operations between 20m and 10m. Right now I have a decent setup with the vertical Buddistick in this range. It is easy to deploy on either band. The homebrew Buddistick has worked great on 10m. The jury is still out on 20m as I have not tested it much yet. The next iteration is a homebrew Buddipole dipole antenna. The EZNEC studies show better 10m performance if the dipole is at least 16ft above ground. Not much difference between the vertical on 20m but the 20m dipole needs additional height which starts getting tricky. The nice thing is that I should be able to use the dipole as the driven element for a two element Yagi on a short boom. The simulation shows good directivity and significant gain increase on 10m at 16 feet. Once again the 20m version requires more height to be effective vs. the vertical.

This analysis is still a work in process but this is showing the direction I plan to take the antenna work. I will use the Vertical Buddistick as my main antenna system for portable use as it is already built and is easy to deploy. Next step is complete the 10m Buddipole dipole. This will work thru 15m as well by extending the whips. I will go ahead and wind the coils for 20m operation even though it looks like at 20m the antenna will be extremely compromised. Once I have played with the dipoles I can use them as the driven elements for a 2 element Yagi. This should provide the best performance on 10m thru 15m. Stay tuned and I will post pictures and maybe some video on my progress.

HF Portable Antenna Choices

I am quickly settling on the Buddistick as my HF portable antenna option to cover 20m through 10m. The reasoning for this has come from analysis of different configurations using EZNEC. First let me just state this:

“You can’t change the laws of Physics”

Antenna design is a harsh reminder of this. In many ways I am glad I started this exploration by looking at the special case of portable HF antennas. The reason for this is that portability imposes some interesting constraints over antennas used in a fixed installation. The first major constraint is height. I set out with the idea that I may find myself in a location without a natural height source (i.e. trees) so that the antenna would need to provide its own support. Portable masts, painters poles camera tripods, PVC pipe…anything that can be compactly packed and then used as a mast. The higher you go the more you also have to deal with stability and that means guy wires. So far I have not dared beyond 8 feet for the feed point of the Buddistick, On 10m this gives me a vertical antenna height of about 20ft and a bit more when configured for 20m.

Doing some calculations on the Buddipole, which is essentially a horizontal dipole shows that for best results I need to get it up at least 16 ft on 10m and considerably higher for 20m. The gains of this configuration look promising and I intend to at least test this on 10m. The vertical may end up being the easiest to safely deploy in the field. A portable beam looks really interesting but the height constraint really kills its use in practice. a 2 element 10m beam is possible but getting this to work on 20m would be a challenge as 16 feet is about minimum.

So for now I am going to focus on the Buddistick configuration for portable HF. I will test the Buddipole on 10m and my ability to setup a 16-23 painters pole as a mast. If I can feel good about setting up the mast I may try the 10m beam but frankly not sure if it is worth the added expense of two long whips.

That still also leaves wire antennas which may be the best choice of all given that the portable mast up to 20 feet can work. I can use a dipole in inverted V configuration as only one support would be needed. Also have an end fed antenna to try in different configurations.

Well I think you see what I will be working on in the short term….

Some additional thoughts on yesterday’s QRP DX session

Did some calculations this afternoon to try and discover what went right during yesterday afternoon’s QRP session. The homebrew buddistick antenna is somewhat directional. The single radial points to the direction of highest gain. When I set up yesterday the direction of the radial was randomly picked and somewhat limited by where i could drive the stake that supports the radial 4 feet off the ground. I thought i was pointing generally in the Northeast direction but it turns out the opposite was true. I was roughly pointing at a bearing angle of 297°. The directivity of the antenna gives me pretty stable gain 90° on either side of that. So the swath of best coverage was between SSW and NNE. So here are the bearing angles of the DX contacts from my QTH:

  • Japan: 318°
  • Brazil: 128°
  • New Zealand: 230°
  • Argentina: 162°

The contacts from Brazil and New Zealand were will within the swath of main directivity. The South American contacts must have been just outside the 180° main coverage. Now what was interesting is that I was also picking up clear stations in South Korea and Australia (though I did not make contact with them). The South Korean station never heard my call at 5W. For grins I ran into the house to try and contact him on my main rig at 100W but I could not hear him on the FT-450D. Not the radios fault! Remember that my main antenna is a horizontal end fed antenna running north south about 20 feet off the ground. I simply do not have enough gain in that direction to pick up that station.

The other observation is that I was not picking up any contacts in Europe during that time as they would have been deep in the null created by the antenna.So when all is said and done the theory matches up with the practice! Looking forward to my next session with this rig and seeing what happens when i point it in different directions by moving the radial around.

Upgrades and Tweaks for the QRP Portable station

I made a few minor changes to the portable QRP station based on the Yaesu FT-817ND. First I upgraded the solar panel to a foldable 60W panel. It spreads out like a tarp on the ground or hangs over a chair. Added some power poles to this for quick and easy changes to the configuration. Also added a second wattmeter for the load side. Now I can monitor what is coming out of the solar panel and what is going to the load. Also swapped out the solar charge controller for a slightly fancier one. It was billed as a MPT controller but looks like it is a PWM controller with an LCD display. The display is nice as it shows what each component is doing.

I operated in overcast skies this afternoon for about 2 and a half hours and made seven contacts. The wattmeter from the solar panel showed .295Ah during that time while on the load side I consumed 1.057Ah. I am sure that on a sunny day the panel would have kept the battery fully topped off.

The Yaesu FT-817ND shows a current draw of 330mA on receive and 1.68A peak during transmit. So the go-box is pretty well set. Just need to get a cheap multi-tool to throw in there as you never know when something will need adjustment.

The big tweak today came with the homebrew Buddistick. I did some EZNEC modeling and found out some interesting things. The main two observations were that I needed to get the feed point higher to at least 8 feet (from the 5 and a half feet I tried last time) and replace the wire in the two foot PVC segment with Aluminum tubing. Both of these result in much better predicted gain and low angle radiation. So off I went to Lowes for a 3/4″ Aluminum tube. It was pretty straight forward to cut it to length with a hacksaw and drill two holes  at the same place in the PVC pipe where the wires came out of. The tube fits inside the existing piece of 3/4″ PVC pipe.A screw on each end holds the pipe in place and serves to connect the wires to the rest of the antenna.

Lastly I had to cut longer pieces of paracord for the guy wires. Straight forward enough, I simply divided a 50ft length into three equal pieces. Setup takes about 15 minutes in my backyard. The antenna tuned up easily using the Mini60 analyzer to about 1.4 SWR on 10m. So…put on my headphones and…the results?

First two contacts were in Idaho for the Idaho QSO party both were 59. Did a bit of tuning and picked up a CQ from New Zealand. He returned my call and I had a 33 signal report! Next was a 57 in Chile. Then picked up a lonely CQ from Japan who reported me at 53. This was followed by a 52 from Argentina and finally a 53 from Japan. The last contact was 7421 miles from my QTH. This worked out to 1484 miles per watt at 5w!

The changes I made seemed to work successfully and this on a day with SFI of 119, SN of 56 and poor predicted band conditions on 10m.

All in all a nice afternoon outdoors working DX on QRP!

Antenna Fever

OK so now I have antenna fever. As I had posted previously I have built and successfully tested a homebrew Buddistick. I have the parts for a homebrew Buddipole that I would like to try next, but now I am thinking more and more about a beam for 20-10m. A 2 element Yagi for 10m seems to be within reach with buddipole components. A reasonably sized 20m will require loading coils. I am working with EZNEC now and will post my progress on design in future posts.