Search found 168 matches

by R. Fry
Sat Aug 03, 2019 5:35 am
Forum: FM Radio
Topic: Willis/Sears Tower FM Coverage Estimate
Replies: 11
Views: 410

Re: Willis/Sears Tower FM Coverage Estimate

As for the "building penetration" of an FM station using reduced ERP with an overheight, low-gain transmit antenna, below is a comparison of the nearby radiated fields from Class B FMs using a 1-bay antenna at 1550 ft HAAT and a 6-bay antenna at 500 ft HAAT. The 50 kW at 500 ft station wins, but eve...
by R. Fry
Wed Jul 31, 2019 6:02 am
Forum: FM Radio
Topic: Omni FM with Parasitics?
Replies: 8
Views: 329

Re: Omni FM with Parasitics?

Two comments with respect to previous posts... Usually the tower distorts the v-pol radiation pattern more than it does h-pol, so if the goal of adding parasitics to an "omni" FM antenna is to produce a better match of radiated ERP in the two planes, vertical parasitics are required (not horizontal)...
by R. Fry
Mon Jul 29, 2019 5:09 am
Forum: FM Radio
Topic: Willis/Sears Tower FM Coverage Estimate
Replies: 11
Views: 410

Re: Willis/Sears Tower FM Coverage Estimate

Bob Gorjance and radio_guru both had good comments in response to Kevin Kidd's question. In my job before I retired as the FM Applications Engineer at Harris I was the technical interface between customers, consultants and various Harris engineering groups, and involved in the FM transmitter and ant...
by R. Fry
Sun Jul 28, 2019 6:37 am
Forum: FM Radio
Topic: Willis/Sears Tower FM Coverage Estimate
Replies: 11
Views: 410

Willis/Sears Tower FM Coverage Estimate

For anyone who might be interested, below is a clip showing a section of a Longley-Rice coverage study for the non-D, ~4kW ERP FM stations on Willis/Sears Tower in Chicago. The study includes the effects of terrain elevations (300-ft horizontal resolution). https://i.postimg.cc/v8nc3VdH/WIllis-Sears...
by R. Fry
Sun Jul 07, 2019 4:10 am
Forum: AM Radio
Topic: Isotron Emergency Antenna STA for AM
Replies: 8
Views: 358

Re: Isotron Emergency Antenna STA for AM

If you can find a place to install even an electrically short vertical radiator and depending on soil conductivity at the site, it may not take much of a radial ground system to make a fairly low-R path to r-f ground for it. Below is a NEC4.2 analysis of such a system, showing ground path R variatio...
by R. Fry
Fri Jun 28, 2019 4:08 am
Forum: AM Radio
Topic: Vertical Monopoles Using Buried Radials
Replies: 1
Views: 302

Vertical Monopoles Using Buried Radials

As an "FYI," below is a set of extracts collected from the textbook Radio Antenna Engineering by Edmund Laport, Chief Engineer, RCA International Division and Fellow of the Institute of Radio Engineers (McGraw-Hill, 1952). Some of its details may be different than popular concepts about the way thes...
by R. Fry
Thu Mar 14, 2019 1:44 am
Forum: AM Radio
Topic: Retune Harris DX10
Replies: 11
Views: 958

Re: Retune Harris DX10

Below is a clip showing the total a-c input power to r-f output power parameters for the Harris DX-10 transmitter: PA AND OUTPUT EFFICIENCY: 90% or better. OVERALL EFFICIENCY: 84% or better. Typically 86% at 10 kW, 77% or better at 5 kW, typically 80% at 5 kW. POWER CONSUMPTION: 11.9 kW or less at 1...
by R. Fry
Tue Jan 01, 2019 7:57 am
Forum: FM Radio
Topic: Horizontal or vertical
Replies: 8
Views: 748

Re: Horizontal or vertical

Below is a comparison of h-pol and v-pol "coverage," for the conditions/methods stated there. The terrain in/around Springfield IL is not very hilly, but the comparison shows differences in received fields — slightly in favor of v-pol. https://i.postimg.cc/fTNWXhws/H-pol-to-V-pol-FM-Fld-Comparison.j...
by R. Fry
Mon Nov 19, 2018 5:29 am
Forum: AM Radio
Topic: Gates 5 rebuild
Replies: 11
Views: 1479

Re: Gates 5 rebuild

Here is a link to a short paper written by Jim Pickard (Harris Broadcast Div) regarding the issues when using open delta mains service:

http://rfry.org/Software%20Download/AC% ... ations.pdf
by R. Fry
Mon Nov 05, 2018 4:41 am
Forum: FCC Discussion
Topic: Knife edge limits for § 15.221 Operation in the band 525-1705 kHz.
Replies: 2
Views: 337

Re: Knife edge limits for § 15.221 Operation in the band 525-1705 kHz.

An unlicensed AM transmit system exactly meeting FCC §15.219 most likely would permit much higher field intensities at the campus perimeter than using §15.209. See below: Note: Some of the assumed 85 mW of output power is dissipated in the radial ground system. Those effects are included in the mile...
by R. Fry
Thu Jun 14, 2018 7:47 am
Forum: AM Radio
Topic: Part 15 AM Signal Coverage Expectations
Replies: 0
Views: 394

Part 15 AM Signal Coverage Expectations

From a post on a "Part 15" website... ____________ A great number of possibilities exist for the equipment configuration and performance of a radio transmitting system. Even when the transmitter power, frequency, and modulation values are the same in each case, these systems can produce widely varyi...
by R. Fry
Sun Feb 11, 2018 4:30 pm
Forum: AM Radio
Topic: Audio Bandwidth of an AM Broadcast Station
Replies: 19
Views: 2118

Re: Audio Bandwidth of an AM Broadcast Station

No doubt, Kevin.

The r-f spectrum shown in my post was produced by an SDR directly from the daytime radiated fields of that AM station, received about three miles away from their tower site.

Their performance clearly may not be representative of the performance of other AM stations.
by R. Fry
Sun Feb 11, 2018 12:28 pm
Forum: AM Radio
Topic: Audio Bandwidth of an AM Broadcast Station
Replies: 19
Views: 2118

Audio Bandwidth of an AM Broadcast Station

Basic information for any somewhat non-technical readers of this board ... _______________ Below is a clip showing the received r-f spectrum of an AM broadcast station, at one instant of time. The carrier plus its upper and lower sidebands are clearly visible. The two sidebands are mirror images of ...
by R. Fry
Sun Feb 11, 2018 6:41 am
Forum: Ham Radio
Topic: Affect of Earth Conductivity on a Monopole Antenna System
Replies: 0
Views: 479

Affect of Earth Conductivity on a Monopole Antenna System

For anybody interested ...

Below is a graphic showing how earth conductivity affects the radiation pattern/gain of a base-fed, unloaded, λ/4, 40m, monopole antenna system, over the range of very poor to very good conductivity.

Image