I see KLVV is in Oklahoma City. I presume your new station isn’t going to be further north, but if it is, and antenna icing is an occasional consideration, a high power ERI Rototiller is the way to go. Even without radomes, the 3 inch diameter radiating elements do not detune nearly as quickly as a Jampro Penetrator when covered with ice.
A medium power ERI Rototiller is a good choice as well, but they will bend with heavy icing. I have one that has been on the tower in extreme northeastern Montana since the early 80’s at 2 kW input, now 4 kW input, still very little reflected power, still holding pressure well. That site does not get icing like the mountain tops in western Montana. K-Love has an ERI medium power 2 bay 2 station combined antenna with radomes on TV Mountain near Missoula, Montana that has survived a few winters with heavy icing. Time will tell.
I won’t put up a Shively without radomes. The heaters do not protect the feed straps and they go out ouf tune quickly. I have 3 6813s, two 4 bay and one 6 bay. Shively modified the design of the medium power antenna about 2011 or 2012. They went from 2 ¼” interbay lines to 1 5/8”. I had the brand new six bay antenna at 450’ AGL break at 3 welds in a late spring blizzard in western North Dakota with days of installation. Its replacement has survived six winters but I keep a wary eye on the line pressure alarm in the winter. Shively also raised prices in the last 5 years making them less attractive.
The main advantage to the Nicom besides price is that it is an unpressurized system. As was mentioned, SWR tends to be a variable thing. I have a 2 bay at 90.7 on the catwalk of an old AT&T microwave tower that has very low SWR, and single bays that are in the 1.3:1 range. I always go with the 7/16 DIN connectors on the Nicom BKG-77s as they seem to be more rugged than the N connector models and the connector price isn’t much different. We have built a few Nicom arrays that we bought the radiators from Nicom, built our own equal length lines out of Superflex or LDF4-50, and used a Bext power divider. I have used several Nicom power dividers but have sealed the top cover with RTV so that driving snow or rain can’t get into them. Some we have also drilled a weep hole near the input connector as well. The BKG-77 with the mini-radome is surprisingly resistant to detuning from ice buildup.
Just a few random thoughts from the past 30 years of building and living with what I built or what I inherited from someone else.
Ron Huckeby, CBRE
From: Scott Todd [mailto:firstname.lastname@example.org]
Sent: Tuesday, April 03, 2018 12:32 PM
To: CRTech <email@example.com>
Subject: [CRTech] RE: What do you recommend for FM transmitter antennas?
Best coverage is usually with a rototiller or slanted arrow types. This is particularly true with hilly terrain. Ring stub types are best over flat terrain. My company uses ERI for higher power installs (full class-A and up) almost exclusively. They’re not the easiest to tune, but once they’re set they perform well. For something like this I’d not use the Nicom, presumably the BKG-77. We use a lot of them on lower power installs including translators, and while they work OK, I’m not happy with the VSWR at the band edges. VSWR approaches 1.3:1 especially at the bottom of the band. They’re indispensable if you’re doing a diplex or triplex, though.
From: Dave Land [mailto:firstname.lastname@example.org]
We're looking at putting in a new FM station soon. I'm wondering what folks prefer for transmit antennas on a budget! This will be a 6,000 ERP station with about 4,000 TPO so a 4 bay antenna. We're looking at - BEXT, Dielectric, ERI, Jampro, Nicom, PSI, Shively, & SWR. Which do you prefer and why?