Hello,
Hello,
I am still fairly new to operating a part 15 transmitter. My transmitter works well and with a 10 foot copper wire antenna, I get about a 150 - 200 ft. range. I use a Ramsey AM25. if you read my station listing, I operate at 1490 kHz. I am trying to start up a community radio station, but when it comes to the antenna, I am very confused.
I have seen many ideas and plans, and I really don't know which one is right for me, I would like to cover anywhere from 1/4 mile to 1/2 mile area, to cover my neighborhood. I am not sure if I completely understand how to build the antenna.
If anyone has any advice, I would greatly appreciate it,
THANK YOU VERY MUCH!
The biggest improvment over a simple wire antenna will be to add a base loading coil and adjust the coil and wire to resonance by changing the taps on the coil. The front page of this site shows a manufactured coil which could work.
More information on building your own coil, antenna, and ground plane can be found on the SSTRAN site by clicking the SSTRAN logo on the left side of this screen. If you want to dig deeper into the theory try this link:
http://lpam.info/index.php?page=antennas
I have used the AM25 with a base coil and it did extend the range quite a bit. I also tested the RF output of this unit under various load conditions and found it to be very tolerant of different antenna loads. It should work well with a coil.
Neil
Why not center loading? More efficient.
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For those who are interested, here's a link to a thread which has information on center loaded short antennas:
Neil
I have been researching some more about the topic, and I think that it would be best for me to experiment with a few differnet designs before I make a choice.
I am writing to ask what anyone thinks about the idea for the antenna that comes with the AM25. It involves wrapping about 120 turns of wire around a 1.5 inch diameter PVC pipe and attaching a 102" CB whip to the coil.
I figure I will try this first, but like I said, I'm wondering if anyone would recommend this.
Thanks Again.
This would be a good place to start. Unless you have the CB whip you can save money by using a wire and if you are satisfied with how it works you could then get the whip or a copper pipe.
The idea behind a loading coil is to use the inductance of the coil to cancel the capacitance of the short antenna. When done properly (that is, when at resonance) the only load the transmitter output will "see" is resistive and, in theory, this will provide an effective transfer of power.
Without digging out my AM-25 manual and going only on memory I don't recall them mentioning tuning the coil/antenna. Even if not tuned, the coil inductance moves the radiating system impedance in the right direction providing the coil inductance is not too high. My experiments with a tuned matching network, not a simple coil, shows a very sharp resonance accompanied by a marked increase in signal strength.
I think you will find an improvement with the coil in the system but if you want to push it further put taps on the coil and try different ones until you get the best performance (usually at resonance). An oscilloscope is a great aid in this adventure and if you have one available I will be willing to post how I use mine as a field strength meter for tuning the antenna (rather than doing so now which would make this post quite long).
Neil
Hi again,
Two days ago I build my loading coil. It consisted of enamel coated wire wrapped around a 1.5 inch PVC pipe. After the first 30 turns, I started making tap points at every 10 turns. In all, I had 12 taps. Tonight, I hooked up my antenna (102'' CB whip) to my coil and transmitter. Once I found the best tap, I hooked it to it and instantly my very sensitive AM radio picked up the signal crystal clear. My whole house recieved the signal perfectly. I thought the best of this.
Then I went out to drive around the block to see how far my signal reaches. I tuned my car radio to 1490 Khz and out of no where, my signal was gone. Right in front of my house I was able to pick up a tiny bit of my signal mixed with the loud roar of the frequency. I lost my signal completely about 10 feet from my house. How can it work so perfectly inside my house and so badly outside. I live in Scranton, PA and the closest 1490 AM is in Hazleton, PA. (About 30 some miles south.) During the day, I cannot recive this station at all. I am wondering if the scattered bits of noise mixed with the dead air at night is from theat station and if it is drowning out my signal. I also can recieve stations at night from the Binghamton, Philadelphia, Harrisburg, and New York City markets if one of them could be reducing my signal.
I was just wondering if you had any ideas based on this.
Thanks again.
Now, I saw plans for the SSTRAN antenna which looks fairly simple to construct. The plans are detailed (believe me, I need that) and it seems to work for my need. I also saw that it is not compatible with the Talking House transmitter or the Rangemaster. Is it compatible with the AM25 from Ramsey, I hope?
If anyone knows, please let me know. Thanks,
each have internal inductors to load the antenna output, so the loading coil on the SSTRAN Antenna plan would add another inductive load which would be far too much inductance.
Strictly speaking, many Talking House models do have a second external antenna connection that does not use the internal inductor, for the purpose of using a Talking House "external antenna and matching circuit" sold separately.
That connection could theoretically be used for the SSTRAN Antenna but then it is likely the unit would not meet its FCC certification requirements and it would be a non-certified experimental transmitter - like the AM25.
The last time I saw an AM25 schematic I don't remember seeing any internal matching circuits, so the SSTRAN antenna could be useful.