Another thought on the Antenna .
There has been past discussions about using a copper pipe.. it seems they were all for the positive. I do recall that somebody had replaced their 102" whip with a copper pipe on a Rangemaster and claimed that it made the received audio sound fuller, but no noticable improvement in range was acheived.. I don't know, never tried it, but am curious if antenna diameter could actually have affect on the audio quality
Search "copper pipe" at the top of the page in the search box
Rich I have been reading this concept over the past two hours and it looks like the Bandwith will improve a great deal with this concept and that alone might be a reason to try this.
I think I am going to give it a try VS the Whip and see what I see.
Yeah, I re-read a few of the old post too. It does sound promising
But what is "VS the whip"??
I also have read that the bandwidth of an antenna is more narrow with a thin metal, be it a whip or a wire; wider with a thick pipe. The technical term for the resonant range of an antenna is the "Q."
But how large a diameter does an AM medium wave antenna need to be for an easy bandpass of 10kHz or 15kHz?
Take an audio frequency response graph using a whip, and then using a large-diameter copper pipe.... compare the difference.
The measured input Z of my outdoor base coil loaded 3 meter vertical (1/2 inch aluminum pipe) above ground radials antenna is measured as 57 + j0 ohms. The j0 means it is resonant and this was measured at 1680 kHz. The loading coil inductance (L) is 260 uH.
From this the antenna system bandwidth can be calculated as BW = R/(2*pi*L) which equals 34.9 kHz so the audio high frequency cutoff for AM is half this = 17.5 kHz.
As an experiment, the audio cutoff of my transmitter was measured to be 20 kHz measured at the output of the modulator at the input to the final RF stage. The receiver, a BC-1004-C, has a measured audio cutoff at 17 kHz with the IF wide open. The overall system bandwidth from transmitter audio input to receiver audio output was measured as 17 kHz (high cutoff) so the receiver BW dominates and the transmitter/antenna system BW is at least greater than this.
For my installation, increasing the diameter of the pipe would have no noticeable effect and is not worth the effort.
To repeat this calculation using the AMT-5000 the audio bandwidth of this transmitter needs to be known and also the Q (or RF resistance) of the loading toroid needs to be known. The Q of my loading coil was measured to be 147 (R = 19 ohms) so if the AMT-5000 specs. are similar then similar results would be expected providing the antenna system R is comparable to my 57 ohm reading.
Since the Q of the loading toroid and the audio bandwidth for the AMT-5000 is not known to me I cannot make an accurate prediction but I expect that if your ground resistance is comparable to mine then the bandwidth will be adequate using a 1/2 inch diameter radiator.
The only sure way to know is for you to try a narrow and wide radiator and do a "listen" test or better yet a measurement of bandwidth for any difference. If a difference is found then the good news is that a lower bandwidth means lower losses compared to my system.
Neil
Neil Radio8Z touches upon something we tend to overlook, and that is the bandwidth of the receiver itself.
Plain garden-variety AM radios are probably likely to have a bandwidth of about 5kHz.
Better radios sometimes have two choices: wide and narrow.
This TECSUN PL-310 has something unusual, a whole range of choices: 1, 2, 3, 4, 5 and 6kHz. At least that allows sampling the difference in quality among these differing widths. Of course 1kHz sounds very dull and lacking in highs, 6kHz sounds clear and "normal."
Question is, why transmit more bandwidth than ordinary radios can reproduce?
Question is, why transmit more bandwidth than ordinary radios can reproduce?
Frequency drift perhaps? I remeber as a kid listening to am stations in the late hours and having to frequently notch the dial a tad to left or right to pull it back in as the station would start to fade.
Unfortunately radios now, it seems, mostly have just push button tuning, making it difficult to fine tune for weak stations. TV sets too.
Well I have two radios with AFC (Automatic Frequency Control) permanently set by the manufacturer, but the trouble with both radios is that the AFC drifts! I constantly have to retune the dial, but soon it drifts to the edge and the "S" sounds start to slash!
Can't we all just get along with decent radios?
I vote for wide bandwidth, for those radios that can handle it. The cheap narrow bandwidth radios will still pick it up, just not all of it.
But the question is, HOW wide do we dare put out?
Some of the thoughts I have are rather deep when it comes to our station.
I would like to get AM Stereo on our stations and get small producers of radios to make and sell radios for wide bandwith for our stations.
yea I know it's a long shot , but I am looking at ways to bring AM back to the people with content that makes them want to listen.
Normally an AFC circuit (whether drifty or not) was included only in older generation FM broadcast receivers using analog tuning, and were not necessary, or used in AM broadcast receivers. Modern FM receivers using digital tuning don't need/use them, either.
But the question is, HOW wide do we dare put out?
Most, modern, monaural, analog AM broadcast receivers do not reproduce audio frequencies greater than about 4-5 kHz -- so there would be no great benefit in transmitting them.
In my state (CT) there are still a few AM
stations running C-Quam stereo.
KCJJ on 1630 in Iowa still runs
C-Quam - well - as of a year ago.
The chief engineer told me on the phone.
That station has a huge coverage area at night.
KCJJ used to do oldies, but now they are
news/talk. I wonder if you can hear C-Quam stereo
in the music contained in the commercials and promos?
I used to get KCJJ but that channel is blocked now.
Radios for it? Yeah, I guess that's a problem. I have
an old Sony SRF-A100 from 1983 that has seen much better days.
I guess you can buy (maybe) a Sony SRF-A300 portable directly
from Japan that gets C-Quam. These radios are still being manufactured.
It's very pricey it think. $200??? I don't know. If I had the money I
would probably get one.
Bruce, DOGRADIO
P.S. I always used copper pipes for my Part 15
AM antennas. But since that's all I did, I have
nothing to compare them to (i.e. whips, or wires).
Neil, in the picture of your station
set-up on the ALPB website, you have
arrows pointing to 2 different receivers
for monitoring the AM broadcast band.
I can see the BC-1004-C there on the
shelf. There is another radio on a lower
shelf that you use for the AM BCB. I don't
remember if you ever told us what it was?
So, I guess I'm wondering - what is that other radio?
Bruce, DOGRADIO
I have a few very informative charts that contain extra useful information about audio frequencies. Two of them in particular are:
1.) Chart of Musical Instruments Pitch Ranges - The Instrumental Spectrum -- Figure 7-1, Page 157 from a musical reference book (I didn't jot down the name of the book back in 1990);
2.) The Audio Spectrum, Figure 1 from a TV Technology article by Dave Moulten, 4/1/2010.
Let's look at voice.
The fundamental pitch of human voices, from bass to soprano, spans 82.407Hz to 1,046.5Hz. Well within the AM footprint.
1,046.5 up to 2,560Hz contains major harmonic content and spectral identifiers.
2,560Hz up to 5,120Hz critical vocal range including presence, "edge" of hard consonants, primary recognition range for voice and words.
5,120Hz to 10,240Hz vocal sibilance.
From these charts we can understand why AM is considered the band for talk programming.
From these charts we can understand why AM is considered the band for talk programming.
Probably this perception is related to the point that an audio bandwidth of 5 kHz or so includes the more important spectral components of human voices.
In practical terms it is also related to the fact that the FCC allocation plan for AM broadcast stations does not provide r-f channels permitting ~ interference-free audio bandwidths greater than 5 kHz for analog AM broadcast stations -- particularly at night when strong skywave signals may be present on adjacent channels.
For this reason (interference), the manufacturers of most consumer-level AM broadcast receivers have restricted their r-f and a-f bandwidths so as to minimize such interference, meaning that they have little audio output above 4 to 5 kHz.
However this does not mean that AM as a process is incapable of transmitting baseband frequencies much higher than 5 kHz, or that AM receivers cannot detect baseband modulating frequencies above 5 kHz.
For a common example of this, analog NTSC TV transmitters used AM to transmit video baseband frequencies extending from about 60 Hz to about 4 MHz.
TV receivers using that standard had no problem receiving and displaying that bandwidth, because the FCC allocation plan for those TV stations was designed to permit it.