Radio Frequency vs. Power

[rfry]

I've completed a "Current Study" (as KROU is currently licensed to operate) and posted it for you. It's a greatly detailed coverage projection that takes all terrain obstructions into consideration and, if you look closely, you can tell where high and low areas of ground are simply by the amount of RF that gets into each area.

Was your coverage study based on a perfectly omni radiation pattern from the antenna? If so, the result could include significant errors in some sectors, because the azimuth radiation pattern of a side-mounted FM antenna almost never is truly omnidirectional.

The elevation pattern of the antenna as installed also does not closely resemble the free-space elevation pattern published by the antenna manufacturer, and that may affect the conclusions drawn from these coverage studies, also.

Paper 6 at http://rfry.org shows examples of this for two mounting situations.

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[OKCRadioGuy]

Thanks for the map! That pretty well proves what I've been hearing. It doesn't even show the primary red coverage to the city center of OKC, and lots of non-red in S. OKC and out west. For the record we are running a 3-bay Harris(ERI) FML-3 rototiller antenna http://www.eriinc.com/products/rbs/Harris_FML_Brochure.pdf currently mounted on the SE side of a 1500 foot TV tower. Unfortunately I don't have the face size of the tower we're on handy. Changing the mounting of the antenna would be the first thing to do in fixing the signal, even if we had to keep the height, location and power. I just became CE of the station a bit over a year ago and wasn't around when they put up the antenna back in the mid 90s. One consideration for us would be to move southward a bit to excape a short-space issue to the north of us. With that in mind it would probably be good to make the rest of the maps from these coodinates: 35°32'51.47"N , 97°29'30.06"W. There are several towers in that area that might be a possibility so that particular one is sort of of in the center of that group of towers. It would be interesting to see what 152meters at 2.65KW would do. Also at 213 meters and 1.35KW would do. My guess would be that 274 meters and 790 watts would be too little power to get into buildings. THANK YOU for the info!

 

[littlejohn]

The first step is to have the antenna optimized to the tower. As several have pointed out, side mounting will usually result in an aberrant pettern. It can be optimized quite well though. This isn't a particularly cheap operation, so know where the antenna is going to end up before you pay for optimization. Also, if it's to be relocated, it's much easier to mout it as optimized than to come back anbd move/add/etc l;ater.

 

[CW]

If you're out in the tower farm, I'd run the thing up as high as I could get it. We put KKNG on there so it wouldn't overlap KWEN when we moved it to Sand Springs. Knowing we were selling KKNG. When it first went up there, the rigger got one of the bays upsidedown... you couldn't hear the thing in the parking lot hardly. It did improve a bit when he corrected it.
ERI put something you dint like? I've always had good luck with their stuff. Including their panels and cavity backed stuff.
There used to be a family of skunks who lived up there, we often watched Mama lead the kids around the towers. From a distance.
I'll be in TheCity (well, Blanchasrd anyway) in a couple weeks, and then over to Tulsa, gonna see some of the old radio types from Back When.

Didnt CC have an abortion from ERI on a new master antenna they put up about 7 yrs ago and it didnt work worth a crap??? I seem to recall Mike at KATT telling me NOONE was impressed with that ERI antenna.....

 

[OKCRadioGuy]

At the suggestion of Bob Groome a couple months ago I took a look at some of the ERI pattern studies done for others in their database close to frequency and tower size, etc. Our current placement on the tower certainly is a hinderance if what I'm seeing on similar tower faces and placement is any indication (should be). The interesting thing is how many holes are in the signal even if the antenna was a truely omni signal from our present location (which it's not of course). I would think 200 feet or more would do wonders along with doing the right thing and either doing a study or getting one close enough for antenna placement. I'll be real interesting to see the predicted coverage at higher heights and what effect that factor has.

 

[OKCRadioGuy]

"Didnt CC have an abortion from ERI on a new master antenna they put up about 7 yrs ago and it didnt work worth a crap??? .. NOONE was impressed with that ERI antenna....." I think they had some issues with the American Tower site for CC if I recall at first with some of the combining stuff but the signal was OK on it. It's been a while but I think ERI got the problem solved for them in a reasonable amount of time and it seems to work fine around town now. The new combined Richland site works alright away from the tower a bit, but I personally have heard plenty of areas within the first several miles from it where the signal is less than stellar. Out in the fringe it works great of course due to height.

 

[Play Freebird]

At the suggestion of Bob Groome a couple months ago I took a look at some of the ERI pattern studies done for others in their database close to frequency and tower size, etc. Our current placement on the tower certainly is a hinderance if what I'm seeing on similar tower faces and placement is any indication (should be).

One of the Class A stations I worked for had an ERI single-bay mounted on the leg of a 10-foot face TV tower. It was originally mounted perpendicular to the face, rather than straight off the leg, because this azimuth appeared to hit the center of the market.

We did a drive test which revealed a rather drastic reduction in vertically-polarized field strength about 60 degrees off this bearing. Apparently the opposite leg on that face, spaced about a wavelength from the antenna, was acting as a reflector and introducing phase cancellation in some directions due to the difference in path length.

The station decided to move to a new site and combined into a master panel antenna which seems to have solved this problem.

 

[littlejohn]

Two situations come to mind... both high power G-5 6-bay antenna side mounted on ten foot towers. In both inbstances, ERI got them to within 9 dB or so of circular, and more importantly got the H and V within a couple of dB of each other. And in both instances, managed to narrow the null in azimuth considerably and place it where it did the least damage. Both of these were something like 25 - 30dB out of circular when they started.
I would never sidemount an antenna without an optimization study... you know the tower is going to screw the pattern, you best find out where and how, and minimize it. All the manufacturers offer the service, and do a fairly good job of making things round. If you've never seen it done, I recommend going and watching.