I have a AM 25 from Ramsey. The instructions state to wind a loading coil 120 turns on a 1 1/2 PVC Pipe and connect a 8 vertical wire or a 102" CB whip.
Looking further in various other pages and on other sites on coil instructions, I see others use a 4 to 12 inch PVC and wind 30 or 60 more inches on that.
I have a AM 25 from Ramsey. The instructions state to wind a loading coil 120 turns on a 1 1/2 PVC Pipe and connect a 8 vertical wire or a 102" CB whip.
Looking further in various other pages and on other sites on coil instructions, I see others use a 4 to 12 inch PVC and wind 30 or 60 more inches on that.
Other comments suggest use a 4 inch PVC with taps along the coil.
Other comments suggest using the tapped coil arrangement with a vari-capacitor.
What is the best method? If Ramsey suggests 120 turms on a 1 1/2 PVC, what about SWR issues? Is SWR issues not a concern with the Ramsey kit?
In amateur radio, the transceiver usually folds back the power ( reduces the power) automatically when the SWR is above a certain level.
The 120 turns suggestion does not seem to address what frequencies one will be using...it seems too generic for practical use. Surely 600 khz would have a different amount of turns required than say at 1600.
Also I notice that some say the mast mounted (transmitter) is the best way, yet then would the mast would make the ground too long for legal purposes....or would it?
Would then the mast mounted transmitter NOT count toward the total permitted 3 meters?
If the mast and transmitter is 25 feet in the air, then the ground wire connecting to the mast from the mast mounted transmitter (which is driven into the ground) is only 6 inches, then the rest of the height from the transmitter could be used for the antenna? I thought the transmitter would have to be mounted at ground level to be legal.
And if a capacitive hat is used, in theory it could be used as the total length of the gound and antenna are under 3 meters..thus the cap hat does not add any height to the antenna...any more than a loading coil would....your thoughts?
Lastly, has anyone tried using ham equipment like a MFJ tuner or the LDG auto tuner for part 15 purposes? (I know the connecting coax would have to count to the total height of the antenna)
I want to stay legal and yet not fry the finals due to proper mismatch.
Thanks in advance for your comments...
Welcome to Part15.us!
Part 15 AM is the experimenter's paradise, in part because there are few hard and fast answers.
The conflicting information you are seeing comes from the fact that no one really knows what's best because there are so many variables.
There is a huge amount of information here to draw suggestions from and the least reassuring thing I can probably say, though probably the most accurate, is that when you find something that works - please tell us 🙂
All kidding aside, be sure to search our library and forums and above all, DO SOMETHING. Don't get too wrapped up in the theories, the math or the simulations, that can be paralyzing. Instead, study the info here, develop some theories of your own and give your ideas a try.
Legality is important, but similarly undefined in the area of antenna experimentation. The FCC enforcement database indacates that no one has ever been cited for Part 15 AM antenna and ground designs that are anywhere near within the general scope of the Part 15 regulations.
As you will read here and elsewhere, FCC action tends to be driven by complaints. If you don't do things that generate complaints to the FCC (objectionbale content or radio frequency interference) you will likely be left to experiment in peace.
Above all - HAVE FUN!
Experimental broadcasting for a better tomorrow!
Kyradio,
Scwis gives some good advice regarding reading and experimenting. To help you a bit I offer that I have bench tested the AM-25 on the low power setting with a load from 0 ohms to open circuit and have not had any damage to the transmitter. Unlike many ham transmitters, the AM-25 does not monitor the load with a fold back circuit, but again this has caused me no problems therefore you should not be afraid to try various antennas.
For aesthetics, I mounted my AM-25 board in a metal box. Since I noticed that Q9 (the audio and DC supply transistor for the final, not the final itself) runs pretty hot, I mounted it on the box using an insulated heatsink kit. Since it does not process RF, the EBC can be connected to the board using hookup wire. You might consider something like this if you want to test it at high power.
I have also measured the RF output power for various resistive loads and found that the maximum output power occurs at a load of 23 ohms resistive. Though I have not tried it, this seems to indicate that this would work well feeding a basecoil loaded antenna over buried radials since others have posted that the feedpoint impedance of this type of antenna when tuned to resonance is in the 20 to 30 ohm resistive range.
For these tests, I did not monitor the quality of the modulation so that may be something to consider beyond what I did.
It doesn't appear that the recommended coil you mentioned will resonate with the antenna, but it would reduce the reactance seen by the transmitter and will probably be better than no coil.
I hope this information will encourage you to try some experiments.
Neil
Hi
Here is what I am thinking, If (on page 18 of the AM25 manual) Ramsey suggests using a " 5 - 6 foot wire antenna connected to the center pin of the RF OUT connector will provide satisfactory results". Then the SWR issues are non existant, then in that case their suggestion of 120 turns on a 1 1/2 PVC pipe with a 8 foot radiator would work fine.
I have been reading the archives here and elsewhere. One of my questions was going to be about a helical wound antenna all the way up the PVC mast. Yet I do not see many others taking that approach. If the majority uses a basic loading coil and a 8 foot mast/antenna. then perhaps that would be the best route.
Thanks for the reply.
It is my impression that some hams prefer the helical antenna for mobile work since it is mechanically sturdy, but considering the difficulty of making and tuning one I would stick with the base loaded coil design. The SSTRAN design is not too hard to build from easy to get parts.
I have built one, but have yet to install it so I can't tell you much about how it works.
Presently, I use a link coupled coil loaded antenna with a tuning cap. mounted horizontally on my basement ceiling and working against a waterpipe ground. I use the link coupling to isolate the transmitter audio ground which is through my PC from the cold water pipe ground.
This antenna tunes well with both the AM-25 and the SSTRAN unit and both transmitters give a strong signal around my yard on a cheap receiver. You may not want to replicate what I did and I mention it only to illustrate that there is no harm in experimenting. You might come up with something simpler and better.
Neil
Kyradio,
Scwis gives some good advice regarding reading and experimenting. To help you a bit I offer that I have bench tested the AM-25 on the low power setting with a load from 0 ohms to open circuit and have not had any damage to the transmitter. Unlike many ham transmitters, the AM-25 does not monitor the load with a fold back circuit, but again this has caused me no problems therefore you should not be afraid to try various antennas.
It doesn't appear that the recommended coil you mentioned will resonate with the antenna, but it would reduce the reactance seen by the transmitter and will probably be better than no coil.
I hope this information will encourage you to try some experiments.
Neil
Thanks for the info on the SWR, it would explain the contradictions from Ramsey's AM25 manual.
I am going to stick with the 1 1/2 pvc and do some calculating to see what coil I would need for 1590 khz. Later on I plan to experiment with the LDG Z100 ham tuner. My reasoning is that if the tuner is good from 1800 khz, it isn't such a stretch to 1590.
Thanks for the feedback!
I would like to give something back to this forum. i have been reading comments about audio chains and limiters/compressors. I have been using the Tomass' Limiter 1.0 plugin for winamp.
I have been using a inexpensive (car mp3 type ) Stereo FM broadcaster to attempt to play my talk radio and music files through the house. It really is not powerful enough to cover the whole house, thus my reason for going to AM.
The Tomass' limiter works quite well and properly adjusted sounds like a professional broadcaster. Best of all its FREE.
I tried the Plantronics Volume logic, The FM magic setting is excellent. You can try it too its a 30 day free trial, but after just 5 days you can only use it for 5 minutes at a time. Its $20 to buy it. But doing some research, I found other plugins and programs for free..so I passed on it. Maybe if it was $ 10 I would spring for it.
If you are looking for a editing MP3 files, the MP3 Direct Cut is excellent. Best of all it too is free and very easy to use.
Thanks again!
Hey Kyradio,
If I was you I would build an SSTRAN type coil. There are only 87 turns to make, 13 of them are taps. If you plan on staying at or around 1500-1700 kHz it would work just fine. Though if you want to go below AM 1500 you would have to add more turns (I'm not sure how many). Hope I have helped some.
- Travis
Hey Kyradio,
If I was you I would build an SSTRAN type coil. There are only 87 turns to make, 13 of them are taps. If you plan on staying at or around 1500-1700 kHz it would work just fine. Though if you want to go below AM 1500 you would have to add more turns (I'm not sure how many). Hope I have helped some.
- Travis
Yes you have, I think Lowes/Depot is open tomorrow. Right now I am running a 10 foot wire. Yea the supplied AC walwart is providing some hum, just like others have posted. I'm going to hook up my filtered power supply- should make a difference.
Seems there is a lot of success with the SSTRAN antenna. I need to hook up this properly to see how far I get out. With the Tomass limiter plug in for Winamp this sounds better than a regular radio station. Playing the top hits of 2006 now...
Happy New Year !
First,on the antenna loading coil,I had no luck with the 4"PVC coil,couldnt get any good results.I could not find anything near the 13 volts they called for,best try was 2.3 volts. I wound up using the mast mounted SStrans internal tuning to a 9 foot antenna and got ten times the range. I also had to use a different wall wart as theirs just dies after a short time for no reason. I used Sound Solution for a long time,but it wont do overlaps cleanly,it always tics and sputters.and I never was happy with the sound quality-way too many adjustments! I upgraded to v 1.6,use the AGC and an equalizer and I am much happier! I also went thru my collection of nearly 8000 sound files and normalized them all! Thank god for batching!!! Happy New Year all..... from Radio Free Erie
AM1610,FM 101.5,SW 13.56
Regards,Lee