SWR Illumitron

[brandonb959]

Does anyone here have experience with the SWR Illumitron that claims "Typical random variations are reduced from +/- 10 dB to less than +/- 2 dB"? I am no antenna expert, more of a "tube changer" and "wire crimper" We have a 50,000 watt directional that currently has a 5 bay half-wave jampro that we are less than happy with and they are definitely going to replace it....its just a matter of "what with?" Also in the running is a roto-tiller from ERI with similar claims of +/-2dB random variations....

[Dale H. Cook]

Does anyone here have experience with the SWR Illumitron

Our owner purchased two stations that had SWR antennas. Both developed problems (one failed completely when a boom broke off) and both have been replaced with ERI antennas.

[RGORJANCE]

My first experiences with ERI antennas started in early 1965. Their products have been very good. To wit, a VERY EARLY rotiller was recently replaced after being hit by lightning. It was on the air for well over 30 years with never any troubles! It sat on top of a 400 ft tower on top of a good sized hill. There had never been a single instance of an antenna problem until last year. This particular site had taken devastating hits by lightning since it was built that destroyed phones, phone lines, AC service, numerous xmttr related items, Marti units, remote control, etc.

I can't recall ever experiencing another failure in our area with the ERI antennas.

Fossil

[Kelly]

I agree in staying clear of SWR. So what's wrong with the existing Jampro half wave spaced antenna? Generally I've found the performance of the 'Penetrator' style antenna design to be quite good with excellent circularity and gain. Especially true for the .75 or .8 wavelength spaced versions. Okay granted the heaters are not so great, but if replaced every few years, shouldn't affect performance. How old is the existing Jampro antenna?

[Deep Thought]

"a 50,000 watt directional"

You can throw that +/- 2 dB claim out the window with a DA. They'll generally fit it inside the envelope and make 85% efficiency and send it out the door unless you are vigilant with the manufacturer. What exactly is the complaint with your current antenna? How closely does the DA pattern match the protection envelope?

[awsherrill]

If you haven't already done this, I'd have a rigger go up and make sure the existing antenna was actually installed correctly. If parasitics are even a little bit out of position, it can screw up everything.

One of our class-A FMs (built before I got here) had signal issues from the day it was turned on. It is an ERI three-bay half-wave on a lambda mount. The guys who put it up apparently looked in the parts kit, said to themselves "Gee, what are all these extra pieces of brass tubing for?" and used the extra clamps to mount the transmission line.

Even after we got that part straightened out, it took a visit from an ERI field crew to get the parasitics adjusted correctly.

[brandonb959]

The biggest problem is poor coverage within even our "local" coverage area especially at night. Some nights distance stations will come in on top of us even within about 30 miles of the transmitter while we are on full power (TPO). We recently had a network analyzer rented for something else and decided to put it on this antenna, a tower guy took the readings (I know very little about the devices, as I've never needed one before) he said the the return loss I believe was around 30 dB when he thought it should be closer to 50dB. He also said that it looked like the top 2 bays were behaving differently than the rest. He volunteered to climb up and take a look, but management is already looking to replace. The line was shot about 1-2 years ago and a section of it was replaced, but according to the network analyzer the line is fine other than the fact that it won't hold pressure for more than a few hours. We are also planning to replace the line.

[R. Fry]

A return loss of 30 dB means the antenna system VSWR is about 1.07:1, which is fairly good.

At certain seasons and times of day, distant FM stations can produce signals strong enough to capture an FM receiver on that frequency, even in the normal coverage area of a closer FM station.

If you can borrow/rent a calibrated VHF field intensity meter like a Potomac FIM-71 and take a series of measurements at a radius of about 5 km from your antenna site, that can tell you if your antenna is radiating at least approximately your licensed ERP toward that sector.

[Kelly]

I agree with R. Fry. A field strength study is in order. Either using a FIM, or renting/borrowing one of those GPS tracked Ademat field study units to drive the area recording the field strenth of your and other stations to compare.

I'm not sure how someone using a network analyzer could tell whether a single bay had problems, since with a series fed antenna, you're looking at the impedance of the whole antenna. Now I've retuned plenty of antennas by using a network analyzer to tune each bay on the ground, then fine match the entire antenna, but to identify one bay out of a 1/2 wave spaced array as being a problem? Hmm...

[R. Fry]

Does anyone here have experience with the SWR Illumitron that claims "Typical random variations are reduced from +/- 10 dB to less than +/- 2 dB"? ,,,

This link tells more about that concept: http://www.swr-rf.com/products/illumitron.html

The "random variations" there apply to the elevation pattern, not the azimuth pattern. So whether or not the station is licensed as a directional in the horizontal plane is irrelevant to this claim.

Such antenna arrays produce essentially no sidelobes in their elevation patterns by using 1/2-wave vertical spacing of their radiating elements, each with identical radiation patterns when mounted on the supporting structure (which can be unlikely), using binomial, equally-phased power distribution across the array.

But this antenna configuration may produce much higher fields near the earth close to the antenna site, which may lead to an aggravation of blanketing interference problems, as well as requiring more cost to buy, install and operate the FM transmitter and antenna hardware needed for this system configuration.

For more information about this please refer to paper 5 at http://rfry.org .