Also - let us know how that petition for the license goes - I'm interested in doing the same here... since part15 is kinda a dead idea in the area i live in.
I built an EH Antenna and am feeding it with an SSTran. My design is built on an 8" diameter irrigation pipe with copper sheeting for the upper and lower rings. This design, when placed at ~ 150ft, is supposed to function 80% as efficiently as a 1/4 wave antenna.
Here are some benchmark numbers for you to compare the performance of your EH antenna against. These were generated using the FCC's propagation curves for your frequency, the approximate ground conductivity for land area about 50 miles west of Houston, and an electrical 1/4-wave vertical radiator working against a radial Earth ground connection of ~2 ohms DC resistance (typical broadcast station parameters).
Frequency= 580 kHz
Power= 100 milliwatts
Radiation at 1 mile= 1.9 mV/m
Conductivity= 30.0 mS/m
Results:
Contour level ... Distance to contour
2.000 mV/m ... 0.9722 miles
0.500 mV/m ... 3.7781 miles
0.100 mV/m ... 17.8098 miles[/size:11a5d6f6a1]
I sure wish someone was close by that could help me with this (EH) thing, it is *very* heavy but should be totally legal for P15 applications, and you are not limited to only the upper end of the band, I built mine for 580khz.
The performance claims for EH and CFA designs so far have not been proven by independent means and standard measurement practices -- even many years after their introduction. Their designers have not made that possible.
My suspicion is that if your EH antenna needs to be installed at an elevation of 150 feet in order to get within 20% of the radiation efficiency of a 1/4-wave, broadcast-type vertical, that much of its radiation emanates from its feedline and/or its "ground lead." A vertical radiator consisting of a simple wire of the same electrical length working against the same ground connection resistance probably would do as well (or better), and be much easier to match into.
Of course, the use of a radiator longer than 3 meters, including its feedline and ground conductor, is not permitted for Part 15 AM stations -- no matter whether this consists of simple wires or incorporates other forms of radiators such as an EH design.
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Hi Rich,
I know there are alot of opinions, both pro and con, about the EH design. However, there is a ham club about 80 miles from me, north of Houston, that swears by them. Ted has several different designs, and mine is based on his "small" commercial broadcast *star* prototype. The EH uses no ground system, it's design is supposed to pulse between the uppper and lower rings thus radiating. Tuning the EH is a tedious, pain in the arse, but after numerous calls to others that are using them on 160m and other amateur bands, I do think the design will work.
Two copper "rings" that are each 48" tall, and the phasing coil of about 2" tall, all wrapped on an 8" diameter pipe still falls below the 3m limit of the rules. Not needing a ground system is another big plus, even after I buried a system for my base loaded vertical (built it about a year ago), I was not impressed with the range of about 2 miles in each direction. The EH has nearly matched that range, and it is not even tuned yet..
Without getting an analyzer though, I am at a standstill, and I do not think the el-cheapo Autek analyzer will work for this. AEA is out of my price range, I may be able to get a Palstar ZM30 or one of the Micro908 kits, but money is tight right now and I have been offered a job in Dallas. I'll snap some pictures of my EH and post a link later today if I can, the thing is too huge for one person to handle, and my friends AEA showed we kept missing the mark too high or too low with only tiny changes in the taps, but it is functional.
Radiation efficiency is all that matters with the P15 rules, if you really want your station to have a footprint, you have to tune and tweak and tune.... Unfortunately, this requires more than just a 100mw transmitter and a legal antenna. 🙁
Tom Johnson
http://cat-am.com
Two copper "rings" that are each 48" tall, and the phasing coil of about 2" tall, all wrapped on an 8" diameter pipe still falls below the 3m limit of the rules. Not needing a ground system...
Is your Part 15 tx installed at/near the antenna input? If so, do you have any shielded cables connecting the tx to the power supply and program source on the ground? Then if so, those cable shields are carrying RF current, and can be a (large) contributor to the RF fields that this system can generate.
And if the tx is at ground level and feeds the EH antenna input connector through a cable (coax or otherwise), that cable will radiate.
Ted Hart has stated his concerns/explanations about feedline and cable radiation from EH antennas, which can be a problem -- when the power is greater than 100 mW, anyway.
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The SSTran is inside the irrigation pipe, and I have shielded direct burial cat5 feed the transmitter with power and audio. The whole thing is mounted about 25 feet above the music server running DirEttore. I need to bring it down and seal up some of the holes I drilled, so I will snap some pics in a few minutes.
Tom Johnson
http://cat-am.com
omg. How is it working? That looks really sweet.
My area just sucks for a p15 right now. im pretty envious of anyone who has a running station at this point 🙂
I am getting about 1/2 mile right now, but the antenna is really not even matched. I need to get my hands on a good analyzer, and I think after that it will radically outperform the base loaded vertical (as well as allow us to use the rest of the band). I am hunting for a cheapo Autek right now just to get it a little closer to being tuned. Anyone near Houston have an AEA or other and want to help out??
Tom Johnson
http://cat-am.com
Are there any 2-way radio shops around close to you? Do you know someone who works for one? A field tech usually carries a service monitor around with him and he should know how to use it. If you figure that you can make your adjustments in a short period of time, It may be worth the money for a service call to have a $20k piece of calibrated equipment there for your needs. Maybe you can catch one of those guys at McDonalds and ask him for some "After Hours" help. I was one and I've done it.. 8)
God I pray this thing works out. We sure could use a breakthrough. This is also very exciting news for being able to use the low end of the band. I hope you made notes, so you can share build instructions and parts lists!
Also thanks for the pics, what does the complete assembly look like?
Love to know.