The radio on the shelf is a Yaesu FRG-100 which is a nice communications grade receiver.
The BC-1004-C is the big radio below the oscilloscope. This radio was fungus proofed in 1943 so it was a WWII unit. This is the one which I used for the measurements mentioned above since it has an adjustable bandwidth.
In fact, using the internal five stage crystal IF filter, the bandwidth can be as narrow as under 100 Hz. When tuned to an AM station and using this minimum bandwidth all that is heard is a very low rumble since the sidebands are almost totally removed. I once used this feature to tap into and tune to the 10.7 MHz IF of an FM tuner to detect when the carrier disappeared with modulation which is a very accurate method of measuring the modulation index in order to set the deviation accurately.
The radio just recently was treated to a partial rework with new resistors and capacitors and it really performs well. There is more to do to finish the project but for now it is very usable.
As Rich Fry mentioned there is no inherent audio bandwidth limit to AM and with my transmitter and this receiver the audio sounds better than broadcast FM in terms of clarity despite being mono. This radio has a reputation as being among the best AM receivers in terms of audio fidelity.
Neil
Hi Guys Here what i ran into building antenna and trying out on different am part 15 transmitters.
Copper antenna works well.
But have you try to make an antenna out of brass while i did, out of curtain rods and it worked very well.
My wire antenna worked very well, made of 12 awg.
I also found having a bigger diameter antenna did help.
I also found building a solid antenna seems to work ok. ( which will make antenna shorter do to the k factor or velocity factor which it's called its the size of material used. )
But the biggiest thing i notice is really depends what kind of am transmitter you have and how you build the antenna to the transmitter is how it will preform.
And the only really way you can see the difference is to take a drive.
Here is a prime example i used a rangemaster 1000 and tested with original antenna and took note on s signal.
Then i took the rangemaster 1000 with my 12awg wire antenna design and took notes on s signal.
The original rangemaster 1000 102 inch whip beat my 12 awg wire antenna design in the s signal report hands down at the same distance and height. NOTE: (the receiver was at 25 feet away from transmitter in test. )
But when it came to the driving around test my 12 awg wire antenna, was stronger in audio and filled in gaps where the the 102 inch antennna did not cover very well.
I have tested on rangemaster 1000 and procaster and Graymark 533 so far.
Its a trial and error test but have have fun jeff
Let me see if I understand you correctly..
You tested the Rangemaster with first the whip antenna, and then ran the same test with a 12awg wire..
When 25 feet away from the transmitter the whip antenna outperformed the wire antenna.
But when you ran the same test driving around the neiborhood the 12awg wire outperformed the whip antenna.
My first question is how long was the 12awg wire?
My second question; were both test done under the same conditions? Such as same weather, same time frame, same transmitter location, position, power and feed?
My third question is, are you serious?
Jeff, I'm no expert, but I can't imagine how that could possibly be so.
Here is a clip from a 2006 joint study on this subject by the Consumer Electronics Ass'n and the National Ass'n of Broadcasters.
The blue line there is the average value for the frequency response of all the receivers tested.
The receiver audio response curves displayed by Rich are very telling. In fact, those curves are the target for AM stations to serve.
None of them is exactly flat within its range, they are all mid-range emphasized, with the blue (average receiver) being the closest to flat.
The green has a little perk in the higher mid-range, a kind of self-post-emphasis.
But guess what, by using EQ (equalization) it would be possible to make a complementary curve so as to provide a flat response within the available range.
And guess what again. The AMT3000 and AMT5000 transmitters already anticipate the situation by providing a user selectable NRSC Pre-Emphasis which adds a 9.5dB treble boost to the top end.
NRSC Pre-Emphasis which adds a 9.5dB treble boost to the top end.
Adding high-frequency boost to your audio fed to a standard (analog) AM broadcast transmitter can produce a smoother frequency response for the output audio of a typical consumer-level AM receiver.
But the downside is that if your adjacent-channel neighbors also do that to make themselves sound better, they are increasing the interference you will get in the output of a typical receiver tuned your channel. And that greatest interference appears in your channel spectrum carrying your audio range of 20 Hz to 5 kHz, where human hearing is most acute. This result is easily possible at night when skywave signals just above and below your AM channel are maximum.
The graphic below shows why this is true.
Perhaps the NRSC Boost might be safe during daylight hours, but as shown by Rich, perhaps inadvisable at night. Hmmm. Let's go up another sleeve.
Recently there have been several proposals floated by the FCC and others for "improving the AM band."
Many of us feel the proposals are rather flacid and ignore a main problem with AM radio, namely the programming itself. But there is another improvement to consider that I haven't heard anyone put forward: widen the bandwidth for better audio!
The AM band as we know it spans 535 to 1705kHz, a total bandspread of 1.170MHz, with 117 channels each 10kHz wide.
If channel width were widened to perhaps 15kHz there would be room for 78 channels.
But as part of the discussion we can bring in the idea of another band expansion, international treaties perhaps in need of adjustment, to grab space below 540 and above 1700kHz.
Like my idea? Let's get the ALPB involved.
Hi Rich Remember Guys don't stay closed minded about thing be open minded when building antennas you be surprise in results thinking out of the box !
Here are answer to your question i hope it helps you.
You tested the Rangemaster with first the 102 inch whip antenna, and then ran the same test with a 12awg wire.. THAT'S CORRECTED !
( used a national panasonic DR-49 ) Receiver is 25 feet away from the transmitter the 102 inch whip antenna outperformed the 12 awg wire antenna in signal strength. THAT'S CORRECTED !
But when you ran the same test but went driving around the neiborhood the 12awg wire outperformed the 102 inch whip antenna. THAT"S CORRECTED !
My first question is how long was the 12awg wire?
Answer to your fist question: The antenna is about 10 foot long but it's how it's constructed and formed !
My second question: were both test done under the same conditions? Such as same weather, same time frame, same transmitter location, position, height and power and feed?
Answer to second question: EVERYTHING WAS THE SAME , THATS HOW I TEST AND THATS HOW EVERONE SHOULD TEST AND ALSO KEEP NOTES !
My third question is, are you serious?
Answer to third question I'M VERY SERIOUS !
I'll give you an idea, how does commerical am station work, the answer in front of you it runs with either 1 antenna or 2 or more and if you have 2 or more you have a beam antenna!
Here your answer i made the 12 awg wire antenna as a BEAM antenna that's why it out preform the 102 inch whip antenna !
Here is another story i saw in person it was made for 2 meter ham radio handheld it was minature beam antenna Aprox 6 inches long by 4 iches tall, and i heard so many hams say i won't work but i hung around and saw a man hit a repeater 20 mile away with full quieting.
Keep in mind just because people say there no way it will work give a try you will be surprise !
I always had beam antennas and dipole antennas and always had found beams preformance are way better than dipole antenna and think about using horzonital antenna they will give you more range than a vertical antenna.
have fun jeff
The NRSC standard is downloadable at http://www.nrscstandards.org/SG.asp (you can type in any name and any company name) . The document is titled: NRSC-1-B NRSC AM Preemphasis/ Deemphasis and Broadcast Audio Transmission Bandwidth Specifications September, 2012.
The standard specifies a maximum audio bandwidth of 10 kHz for non-IBOC AM transmitters. It also specifies the characteristics of the audio filter required to attenuate audio above 10 kHz. It's a very steep slope low-pass filter often called a "brick wall" filter. A receiver pre-emphasis audio response curve is also specified, and receivers are to be designed with a matching de-emphasis curve to produce a final flat response. There is no FCC enforcement for receiver de-emphasis, so receiver audio response is all over the place, mostly poor.
The FCC does not allocate frequencies to stations within daytime range of each other that are 10 kHz apart (first adjacent channel). So, there will be at least 20 kHz spacing allowing for 10 kHz audio (20 kHz RF bandwidth). Nighttime reception can bring in stations on adjacent channels.
The standard specifies a MAXIMUM audio response. A station may choose to limit their audio frequency to less than 10 kHz to concentrate their power in the "sweet spot" for voice.
There is no FCC rule covering Part 15 AM transmitter bandwidth. But, it is stated that there is to be no interference to licensed broadcasters. If you can find a frequency in your area that doesn't have local stations within 20 or 30 kHz, you are free to increase TX bandwidth appropriately.
A really good audio bandwidth can rival FM quality, but only with a super-wide bandwidth receiver. I have one of the original GE Superadio III's that has a wide-bandwidth switch (not one of the newer RCA Superadio III's without the switch). It really does have extremely wide bandwidth to the point that it's almost useless. You need a very strong signal for noise-free reception. It does indeed make my transmitter sound like FM, but it is only practical within a short range of the transmitter.
Part 15 AM antenna Q is a real Catch-22. The higher the Q, the better the range, but the narrower the bandwidth. The "sweet spot" for best range and fidelity is a compromise. Given the crippled audio response of today's receivers, its probably best to go for higher Q to increase the range.
As PhilB noted, the FCC does not assign stations to adjacent frequencies for any one city of license. But there are many cases where adjacent stations can produce daytime interference to each other in common areas where they can usefully be received -- especially if they transmit the full 10 kHz NRSC bandwidth.
Below is a screen clip showing a small part of the upper Midwest with examples of this. Other parts of the country have even denser populations of adjacent-channel stations with overlapping daytime coverage areas.
These circles must not actually depict coverage areas, as I would expect varying coverages, due to differences in ground conductivity. Michigan alone varies from a conductivity of 2 to 15 millimhos/meter, which would result in non-circular contours for most of these stations, I would think. This can be checked on Radio-Locator. But it does give a good idea of how stations are shoehorned in with each other.
These circles must not actually depict coverage areas, as I would expect varying coverages, due to differences in ground conductivity.
Correct. They are based on the radiation patterns of those stations, only, and do not account for earth conductivity.
But at these frequencies and for the omnidirectional, 1 kW daytime power of most of those stations, ground conductivity is not a big factor in the circularity of their 150 µV/m contours -- which contours are about the limit of their useful (interference-free) daytime coverage areas.
The graphic below shows the 150 µV/m contours for the 1240 kHz stations in that region based on their radiated powers, and the earth conductivities shown by the "M3" FCC conductivity map for that region of the US.
Stations operating at 1 kW using omni patterns on 1230 and 1250 kHz have very similar effects due to ground conductivity, so those 150 µV/m contours would be rather circular, as well, and can overlap/interfere with the 150 µV/m daytime contours of the nearest stations on 1240 kHz -- and vice-versa.
Like many PhilB posts, the above note on NRSC AM PreEmphasis is a printout for filing in my AMT5000 file-folder.
This last paragraph is packed with important meaning:
"Part 15 AM antenna Q is a real Catch-22. The higher the Q, THE BETTER THE RANGE, but the narrower the bandwidth. The 'sweet spot' for best range and fidelity is a compromise. Given the crippled audio response of today's receivers, IT'S PROBABLY BEST TO GO FOR HIGHER Q TO INCREASE THE RANGE."
Now, me Carl Blare speaking, I would like to tack-on what I think is an important COMPANION IDEA to support the practice of INCREASING RANGE THROUGH BETTER Q.
I have found that certain careful equalization of narrow bandwidth audio can sound surprisingly clear and life-like. The perfect example is a small loudspeaker in a portable radio that sounds amazingly rich.
I might have an article or two in my audio files regarding the science of tailoring an audio curve to maximize the audio output from a small loudspeaker.
If the AM transmitter is viewed as a small loudspeaker, I believe it is possible to maximize the Q (range) and the fidelity (apparent audio quality).
I'll return to this theory as soon as I can locate some documentation.
I'm an AM DXer and I
spend a lot of time on
the local channels.
1230, 1240, 1340, etc.
Very cool!
Bruce, DOGRADIO
Glad that you found them interesting, Bruce.
From the number of stations assigned to those local channels, it would take an unusual combination of receive system hardware and alignment, propagation conditions, and operator skill/patience to identify any single station using one of those carrier frequencies for nighttime reception at points located more than about 15 miles from the nearest station using that carrier frequency.
When I tune here to any of those local channels at night, all I hear is a lot of "trash" with no single station identifiable above the din.