• Get involved.
    We want your input!
    Apply for Membership and join the conversations about everything related to broadcasting.

    After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
    If you use a disposable or false email address, your registration will be rejected.

    After your membership is approved, please take a minute to tell us a little bit about yourself.
    https://www.radiodiscussions.com/forums/introduce-yourself.1088/

    Thanks in advance and have fun!
    RadioDiscussions Administrators

ERI .78 spacing

F

fm-engineer

Anyone here ever custom space a multi-bay ERI rototiller at .78 instead of using half-wave? Seems half-wave spacing is becoming popular again but I'm still not sold on it. I've found just as many engineers that have regretted half-wave spacing compared to others that think its the best thing they ever installed. This particular installation is in hilly terrain with the antenna about 650 feet above the main service area. I've read about some fractional spacing of Jampro's at .78 with some very good results.
 
ERI will be glad to quote you an array of Rototiller[SUP]®[/SUP] elements having 0.5λ, 0.78λ, and other (practical) vertical spacings, and to send you the calculated, free-space elevation patterns for those arrays.

Then you and/or your consultant can select whichever configuration thought best to meet the needs of your particular installation.

Just to note that (other things equal) most of the difference in the field strengths for those various element spacings occurs within the first ~ ten miles of the antenna site.

Suggest that for best performance no matter what the vertical spacing of the elements, the azimuth pattern of the array should be measured by the antenna OEM when mounted on an accurate physical model of the supporting structure that will be used for it at the transmit site.

R. Fry, CPBE
http://rfry.org
 
Agree on the pattern study and near field signal strength differences ~ 10 miles. Class A FM with a 30 year old Shively, 4 bay, full wave spaced. It is a very narrow bandwidth antenna. Two goals on this proposal. Lessen near field multipath conditions in hilly terrain by focusing energy on the main lobe and eliminate some of the downward radiation of the side lobes. Of course, the concern is reduced signal strength at ground level in the main service and population area which averages 400 to 600 feet below the antenna, and is within the first ~ five to ten miles. Second goal is to increase bandwidth to improve IM and synchronous noise, and improve any phase delay problems caused by a long coax run (about 680'). Looking at ERI 4 bay rototiller which will easily improve bandwidth, but at full wave spacing, also has side lobe characteristics similar to the Shively. Some studies of fractional spacing has indicated .78 delivers a reduction of side lobe energy similar to half-wave but with only a moderate loss in gain. There is also an natural increase in bandwidth, but that really isn't an issue with ERI's. ERI will build at .78 on a custom order but they favor using half-wave over .78 or other fractional spacing options.
 
fm-engineer said:
... Some studies of fractional spacing has indicated .78 delivers a reduction of side lobe energy similar to half-wave but with only a moderate loss in gain. ...
Click to expand...

But whatever the max, published, r.m.s. gain of the transmit antenna system of a non-D FM station, all such stations are required to radiate the nominal ERP for which they are licensed -- regardless of whatever element spacing of the transmit antenna, terrain profiles, and multipath issues apply to that installation.
 
Status
This thread has been closed due to inactivity. You can create a new thread to discuss this topic.
Back
Top Bottom