Search found 156 matches

by R. Fry
Sun Feb 11, 2018 4:30 pm
Forum: AM Radio
Topic: Audio Bandwidth of an AM Broadcast Station
Replies: 9
Views: 486

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: 9
Views: 486

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: 84

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
by R. Fry
Sun Feb 11, 2018 6:28 am
Forum: FM Radio
Topic: Singling out 2 stations on same frequency
Replies: 29
Views: 1324

Re: Singling out 2 stations on same frequency

Another approach that might help: using an FM receiver spec'd with a very good capture ratio helps to reject one FM signal in favor of another on the same channel having somewhat less signal strength. A very good receiver might reject an undesired signal only 0.5 dB below the desired signal, while o...
by R. Fry
Fri Jan 12, 2018 6:59 am
Forum: AM Radio
Topic: Low Power AM ATU question....
Replies: 9
Views: 1089

Re: Low Power AM ATU question....

Below are the results of a spreadsheet based on the opening post, and the assumptions shown in the graphic. When this defined system is tuned to resonance, the sum of the radiation resistance, matching coil resistance, and the connection to a "typical" r-f ground for such systems can result in a fee...
by R. Fry
Wed Nov 15, 2017 11:28 am
Forum: FM Radio
Topic: FM range question - coastal mountainous terrain
Replies: 23
Views: 1256

Re: FM range question - coastal mountainous terrain

... I was showing these charts to a veteran Ham Radio freind last night who is also an electronics engineer. ... He suggested that using an array of (for example) 2 or 4 x 3 element Yagi instead of our current type of antenna could give us enough range in that direction especially as we are wasting...
by R. Fry
Tue Nov 14, 2017 9:01 am
Forum: FM Radio
Topic: FM range question - coastal mountainous terrain
Replies: 23
Views: 1256

Re: FM range question - coastal mountainous terrain

... I googled around and found this: https://itstillworks.com/12439428/how-to-calculate-distances-of-fm-transmissions Generally useful, but misses a lot of specifics. I would be interested though to see how much of the blue 45-60 dBuv area turns to light red 60-70 dBuv. There is no way of knowing h...
by R. Fry
Sat Nov 11, 2017 9:32 am
Forum: FM Radio
Topic: FM range question - coastal mountainous terrain
Replies: 23
Views: 1256

Re: FM range question - coastal mountainous terrain

Below is a Longley-Rice coverage estimate for the conditions shown. Other conditions can be modeled (within reason), based on further input.

Hope this helps...

Image
by R. Fry
Tue Apr 04, 2017 5:54 am
Forum: FM Radio
Topic: ERI .78 spacing
Replies: 9
Views: 1000

Re: ERI .78 spacing

Followup -

Here is a link to a paper showing how changing the element spacing and power distribution across an FM transmit array affects the fields near the transmit site, for the conditions given there:

Zero Sidelobe FM Antennas.pdf
(117.95 KiB) Downloaded 101 times
by R. Fry
Mon Apr 03, 2017 5:44 pm
Forum: FM Radio
Topic: ERI .78 spacing
Replies: 9
Views: 1000

Re: ERI .78 spacing

ERI will be glad to quote anyone an array of Rototiller® elements having 0.5λ, 0.78λ, and other (practical) vertical spacings, and to send them the calculated, free-space elevation patterns for those arrays. Then the broadcaster and/or consultant can select whichever configuration is thought best to...
by R. Fry
Sat Feb 11, 2017 5:02 pm
Forum: FM Radio
Topic: 3 Way N-Type RF diplexer question
Replies: 4
Views: 670

Re: 3 Way N-Type RF diplexer question

For further consideration: The channel isolation needed by such a combiner depends upon the ... - frequency separation of the transmitters - mutual isolation of the transmit antennas, as installed - intrinsic ability of each transmitter to reject external, off-channel r-f coupled to its output port ...
by R. Fry
Tue Nov 08, 2016 5:34 pm
Forum: FM Radio
Topic: Theory Discussion: Circular Polarization Vs. Vertical Polarization
Replies: 46
Views: 3554

Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

... If RHCP waves reflecting off perfect conductors become LHCP waves and vice versa, then wouldn't circular polarization multi-path problems be even worse in the cities, where you have tall metal buildings? ... Not if an RHCP receive antenna is used, as it tends to reject incoming c-pol waves havi...
by R. Fry
Tue Aug 30, 2016 6:54 pm
Forum: AM Radio
Topic: Franklin Antennas for MW Broadcasting
Replies: 25
Views: 2836

Re: Franklin Antennas for MW Broadcasting

From an exchange of posts on another website asking me what the dipole pattern would look like if it had 120 ground radials ... ______ I went back to my Franklin NEC model, deleted all of the above-ground conductors and replaced them with the center-fed, 1-wave dipole elevated 1 meter above the comm...
by R. Fry
Mon Aug 29, 2016 5:25 pm
Forum: AM Radio
Topic: Franklin Antennas for MW Broadcasting
Replies: 25
Views: 2836

Re: Franklin Antennas for MW Broadcasting

W2XJ wrote:I suggest you read and analyze the original Franklin Patent.
To whom do you address your suggestion?
by R. Fry
Mon Aug 29, 2016 4:57 pm
Forum: FM Radio
Topic: Whistling Birdie in FM signal
Replies: 29
Views: 2692

Re: Whistling Birdie in FM signal

Not only is there a whistle but I can hear the interfering station's modulation. This is pretty normal for August around these parts. ...

For analog FM broadcast signals, such co-channel interference can be significantly reduced by using a receiver having a very low capture ratio.