- Posts
Hi everyone.
Hi everyone.
I have some general info that somebody might find useful, but because I am legally blind and didn’t do the work all by myself, I can’t give any big specifics. The person who helped me with this has some major family commitments now, and is unreachable (even by me, and I’m a close friend.)
My AMT-3000 has been used with just a 3 meter indoor antenna (no ground) for quite a few years. We wanted to increase the transmitting range. I do have in my backyard a copper pole that sits on an insulator a few inches above the ground. The pole is supported by guy wires, it was just the best I could do at the time.
I have sixteen radials in the ground. The antenna and ground lead are less that 3 meters in length. (Part 15.219.) It took me a long time to put this together.
First, I tried using the AMT-3000 in this set-up, using one of the internal inductors switched in on the board, and then we tuned the transmitter to the antenna, using the variable cap that is just before the output jack. This worked well. The transmitter could be heard about 1000 feet on the car radio, but at that point the strength was almost gone. Still, I think this was good, considering the Q of the internal coil probably wasn’t in the big numbers.
My friend removed one of the internal coils from the board. The one he took out was the biggest one, which allows operation on the low end of the AM band. Since I am not going to operate down on the low end, that coil isn’t needed. (I did save it, though.) Wires were soldered (sp?) to those points. The idea was to make a fairly high Q coil, attach it to the transmitter, via the wires, and switch it in and see if there could be any useful transfer of power to the antenna. (As far as I was concerned, any increase over what we had before would be fine.) I do not have the coil specs because my friend made the coil and I can barely see it. However, it is similar in size and turns to the coil that is meant to be part of the 3 meter antenna that is on the SS-Tran website.
Because this was a jury-rigged experiment, a tap was put on every coil wire. (I know this doesn’t help Q, but this is all just for fun, anyway.) The operational frequency was 1700 kHz. Everything was hooked up and powered up.
My friend switched the coil into the board and nothing useful occurred. He then took a wire from the transmitter board and tried every tap. Our $20 field strength meter showed nothing, except for a tiny tiny reading on one tap.
This was discouraging because the energy output was much less than before. But my part 15 station is not a serious endeavor, it’s just for fun. Then (to make a long story short) we took a big ferrite rod from an old junk radio and just put it into the coil. Suddenly there was a big peak. He just let the coil sit in there, and put a little duct tape in to hold it in place.
The variable cap in the transmitter was also adjusted and there was a little bit more of a peak. We did not put a voltmeter on the tuning indicator test point because we didn’t expect much of anything. The transmitter does sound fine, though, audio is good.
The station has much more coverage now. I have only been able to take a few measurements with regard to range, because I can’t drive and don’t get out much. Our town center is 2000 feet away and the signal is readable all over that area on the car radio. In some places it is fairly loud perhaps 3000 or more feet away from my house. There are of course hot spots and dead spots, but the experiment was fairly successful. Sorry I can’t give more specifics, but you guys who are more technically savvy than I am might find this interesting. If you are not comfortable trying this, then don’t. Or get somebody else who is able to do it.
Lastly, I’m sure that this is not as good as the antenna/coil arrangement on the SS-Tran website, but it is pretty good. It won’t be on the air for very long, though. It is just jury rigged, and will have to be made permanent, if we even decide to do that. Also, if this has been tried before, and mentioned on Part15.us, the above is all moot anyway.
Thanks for reading this you guys. As somebody who is legally blind, and sort of isolated, it is nice to be part of this group.
Best regards.
Total posts : 45366Hi there, this is Micro 1700.
In my original note, I had a slight error. You guys have probably figured out what I really meant, but I’ll mention it anyway.
I had talked about putting a ferrite rod into a coil. There was a peak then and I said we taped the coil in place with some duct tape.
What I really meant to say was that we duct-taped the ferrite rod in place inside the coil when the signal peaked.
Sorry about that.
Thanks again.
Total posts : 45366MICRO1700,
For many of us, experimenting is a big part of the fun of Part15 AM and your detailed writeup of your experiment is appreciated. Thanks for sharing.
Neil
Total posts : 45366Hi Neil, it’s nice to hear from you.
Future plans for the next couple of decades, include restoration of a Gates Studioette board (it’s a real mess),
Remote frequency change for the SS-Tran (because the clearest AM frequency here during the day is not the same as the clearest frequency during the night),
A 13.56 MHz transmitter with reduced carrier (or none at all) and just one sideband, and
Last but not least, tying a scope into the IF strip of a good AM radio for a modulation monitor.
I plan to have these all done by the time a human being sets foot on Mars (HA!). Thanks again, and by the way, my real name is Bruce.
Total posts : 45366Hi Bruce,
You mentioned tapping into a radio IF with a scope for an AM modulation monitor which should give a selective and sensitive modulation display but I have a “cheap and dirty” way to monitor AM which I use here. I attached a 2 foot wire to the scope probe tip and another wire to the probe ground, stretched them out in a dipole shape and placed an RF choke between the probe tip and ground to eliminate the 60 HZ hum but allow the RF through. It is placed about 8 feet from my transmit antenna and I get about 20 to 50 mV peak indication on the scope and can easily assess the modulation as well as the RF waveshape. It could be tuned with a variable cap in paralled but here I found that was not needed. I like this because it doesn’t interfere with the transmitter or the antenna tuning.
Another neat way to monitor AM is to use a trapezoidal display by setting the scope to X-Y mode and applying the antenna RF to the vertical and the audio signal at the final modulator stage to the horizontal channels. This makes it really easy to measure the % modulation as well as to see overmodulation. It is more complicated that a simple time display of the RF and it requires tapping into the transmitter. I just used it for some bench testing and use the aforementioned method for routine checking and monitoring. Do a web search on “AM trapezoidal” and you should get more info.
Neil
Total posts : 45366Hi Neil:
I live in Connecticut but regularly talk on the phone to a good friend in California, who also has a part 15 station with an SS-Tran. He said pretty much the same thing you just wrote, although he didn’t mention the choke.
I haven’t looked at the RF textbooks in a long time – can you let me know at some point what the value is of the choke you have across the scope? I’m figuring it probably isn’t that critical.
I am an AM broadcast band DXer, and I have a wire that runs about 75 feet into the back yard that passes very near to the “Micro 1700 stick.” Maybe I can hook that to the scope and ground the cold side. I guess then I might have to tune it with an LC combination.
I actually have several wires that I phase to hear stations that are “under” other stations.
Anyway, I will bring the scope into the back yard and try it the way you describe. My son will be glad to help me with that. So it sounds like were going to have some fun!
Thanks, Neil!
Bruce
Total posts : 45366Bruce,
I needed to use the choke to eliminate the 60 Hz hum (same as you get if you touch the probe tip) and just grabbed one from the junk box. I would guess that it is in the 1 milliHy range. It looks similar to the chokes used in the SSTRAN for audio ground and power decoupling (L1, L2, and L3). The value would not be important unless you want to tune it to resonance which I do not do. You do need enough inductance so it doesn’t pass AM RF though else it would short the signal to ground.
If you connect to your outdoor receiving antenna you may need to set up a resonant circuit since there will be a lot of RF signals on that wire as opposed to what I receive on my short test dipole. Here, the closest AM broadcast station is about 12 miles distant running 500 watts so I don’t get much AM without an outdoor antenna.
Neil
Total posts : 45366Hi Neil:
Thanks for the info. This will be another learning experience. I seem to have learned more about radio doing this part 15 stuff than any other radio activities I’ve done. (I started TV DXing in 1962 when I was seven years old. My parents, all the kids on the street, and my second grade teacher all thought I was crazy.)It’s a funny thing. As I adjust modulation in the audio chain and out at the “Micro 1700 transmitter shack” in the back yard, I sometimes adjust it wrong – so it is over modulating. If you listen to something for too long, you can convince yourself that it sounds fine. It could also just be fatigue from having a long day doing other things. Then I’ll get up the next morning, turn the station on and at first listen – things will sound terrible. It’s not the SS-Tran’s fault; it’s just me messing with it for too long. So the scope will really help.
Micro 1700 has three listeners:
#1 Me, when I’m walking my dog. (His name is Hoover, we named him after the vacuum cleaner. He eats radios.)
#2 My son, who thinks it’s cool, but he lives in our house.
#3 An actual REAL listener who listens faithfully to it when he is driving around our town. At last check, he could just barelyhear it in his house a mile away using a Kaito 1103, which is a good radio.
If he was using an R-390A with a phased receiving array, he could probably really listen to it. But I am thankful that I have one faithful listener. There are people in my neighborhood that have sincerely expressed interest (which is remarkable by itself) but they don’t have good AM radios, and are a little bit too far away.Besides, as I like to joke about – Micro 1700 is just an experiment anyway.
Anyhow, it is nice to hear from you again, and when I get this scope running, I will post here what I did.
Thanks again, Neil
Best regards, Bruce
- You must be logged in to reply to this topic.
