1. Don't forget you will need a loading coil. The AM-100 output has no tuning and wants to see a low impedance. This is what you get with a series loading coil.
2. Watch out how you interpret the "300% modulation" claim. Actually the plans are quite detailed in describing this feature. 300% modulation is achieved by dynamic power increase. Power increases as the square of voltage, so increasing the peak voltage by 3X increases the power by 9X. A continuous tone modulation at the 300% voltage level is equivalent to increasing the DC power input to 900 mW. The waveform shown in Fig. 6D in part 2 of the plans (and the field strength reading) is the same as you would get with 100% modulation of a 900 mW transmitter.
I read somewhere on the web about an older commercial AM transmitter that had some degree of dynamic carrier power control to increase the carrier power on audio peaks. Present-day (and most older) commercial AM transmitters don't do that, so I guess the FCC didn't like the idea.
Phil B
I built up the AM 100 without the modulation boost in place, At the time discussions were about the distortion it added, and on top of it my knowledge (at the time) of loading coils and proper antenna really wasent that great, so the performance I was getting was like any AM 100 MW transmitter with a ten foot piece of wire without a loading coil, which is in most cases gives about five feet of range.. anyway I havent fired up the AM 100 for some years, I went FM years ago, but now back into AM and know the loading coil is very important and they are easy to build, so am anxious to try the AM 100 again to see what it will do. Of course this means taking it out of that nice box and unsoldering some wires, I hate to burn up someting in the process to convert to positive modulation to get the 300%.
Has anyone used one of these transmitters with a proper loading coil running the transmitter in the 300% mode?
Back then, I built the transmitter and got very short range with it because of a poor antenna system I was using, and like ohters who tired AM, I got discouraged and gave up on it.
I do remember the crystal clear sound of the transmitter. Tuning it up with a 50 ohm dummy load using a scope, all the wave forms looked good and the power checked out where it was supposed to be, Everything was correct, but the problem was the piece of wire comming off the antenna jack. Just a piece of wire and no loading coil didnt do the transmitter justice, years later I figured it all out how to do the antenna system correctly.
By the way, can anyone look at the schmatic of the push pull power amp on the AM 100 and tell me how to convert just that stage to 12-15 volts ( non split power supply) if I made just the amp part? Right now the amp is made for a split 15 volt + and 15 Volt - power supply, with ground ( common )through the bias network it looks like. I would like to take the power amp section and make a small stand alone amp for other LPAM projects, it looks like the parts and circuit shoud be good for at least 500MW ( for a lab amp of course). Ernie liked his split power supplies.
There is a new LPAM antenna at our test facility undergoing test, the antenna requires a 50 ohm input. That is part of the motivation for bring back the AM 100 which has a 50 ohm output. The AM100 as designed built like a rock with fairly common parts and a relatively simple design that should be easy for most kit builders on a tight budget.
Anyone who has owned one, will tell you the transmitter has allot of punch to it. Our AM100's were driven hard and still had a great big bottom sound without distortion.
If the Sstran could be made available with a 50 ohm output, it would be a great companion for the new LPAM antenna and would deliver extended coverage for part 15 AM
Steve
Radio Brandy
Hi Steve,
The SSTRAN transmitter does have a mode to work with a low impedance antenna. This is the mode it runs in with the SSTRAN antenna, http://www.sstran.com/pages/sstran_buildant.html. The mode is set by simply setting all 4 inductor selection DIP switches to ON. This bypasses the internal inductors allowing the loading coil to supply the required inductance in a much more efficient manner compared with the small internal inductors.
The actual impedance of a base-loaded antenna is almost completely dependent on the ground resistance, which can range from less than 10 ohms to near 100 ohms in a typical part 15 installation. When the coil is tuned precisely to the antenna, the coil and antenna reactances cancel leaving just the coil loss resistance (maybe 5 - 10 ohms) in series with the ground resistance.
I would expect that your forthcoming 50 ohm antenna will work with the SSTRAN transmitter, and likewise, I would expect that the SSTRAN base-loaded antenna would work with the Panaxis AM-100.
Phil B
Phil that is really good news! I have not had a Sstran around here for sometime. All of ours were given new homes to get some stations off the ground.
The new antenna would be a perfect companion for the Sstran. Preliminary test using a signal generator shows outstanding performance, now we need to test it with a transmitter for our final test and review.
The combination of the new antenna and a Sstran may provide the most bang for the buck, for those who don't need a certified transmitter, but still want decent coverage.
I will have to work a Sstran into the budget at the beginning of the year to finalize the test.
The meltdown could be good for part 15 AM XMTR sales, just based on the 10 fold increase in traffic coming to our part 15 AM site in the last week. Allot of radio people have been shown the door in recent months, Part 15 broadcasting is a good way to keep the green backs coming in.
Surviving The Meltdown
Steve
Radio Brandy
"I just made contact with my engineer after 23 years, I'm sure he will be on this board soon. He thinks we can pull off the recreation of the AM100, the trimmer cap should not stand in our way."
I'm now on this board. It's amazing how many forums I can find Steve on, now that I know his handle.
When I get the time, I would like to dig out the original AM100 I modified nearly a quarter century ago, and build a new one, 21st century style.
I would like to set up a whole network of the AM transmitters in the area I now live in.
We have many unoccupied AM frequencies here.
In my opinion, Steve had the best sounding part15 I have ever heard.
With the Breakaway Broadcast Processor I have on my computer, plus using Zara Radio automation, I think these little AM's will kick major ass!
I know this thread is old. But out of extreme curiosity, what became of this project?? I had a friend many many years ago that had one. It was quite impressive at the time. I remember it having very strong clean audio. Going through the archives brought some memories back. I have a couple of Panaxis FME500 exciters I purchased from Ernie way back in the day. Still working strong. Would be nice to see a similar kit return.
Brian
"out of extreme curiosity, what became of this project??"
Have not heard anything since that big announcement. I still have my Panaxis AM 100 and Panaxis FM units.
That AM 100 is easy to construct on perfboard and the trimmer cap is replaceable with another type. Extending the frequency range is no big deal either by simply replacing the 4018 with a different divider and crystal.
RFB
Yes, I downloaded the plans. I need to sit down and maybe plan an attempt at building one.
Brian
This past weekend while finishing up a transmitter rebuild project (a dandy dumpster find!), to break out the ol Panaxis AM-100 unit from the TX History shelf.
The unit, after sitting for years without any power, fired right up and on frequency. So I then proceeded to use the Panaxis AM 100 as an exciter to drive an LPB 25 watt amp with the exciter in the 300% modulation mode.
WoW!! That lil ol Panaxis drove the heck out of that 25 watter with pure clean modulated sine wave peaks and nice rounded off neg. peaks and blasted away all the commercial stations in sound!
Think it's time to un-retire that Panaxis AM 100!
RFB
Never up until now has any modulation level above 125% been known to me.
Even this seemed possibly questionable when 100% modulation would be, by definition, a fully formed modulation envelope combined with a carrier.
Like having a wider frequency response than the width of the allowed channel bandwidth, doesn't so much above 100% exceed the bounds of FCC regulations?
How the......300% ?
I don't remember how I ran across this topic... maybe I googled "panaxis"... Yeah, I think that's how I found it... by accident.
I remember sending off my $2.00 for a catalog back years ago.
A Classified AD for "Your Own Radio Station" sparked an interest with me for one reason or another... Perhaps because I wasn't satisfied with the range or frequency drift from that little tube transmitter I had built from The Radio Amateurs Handbook.
I remember flipping through the pages of the educational little catalog, then sending in a check for (seems like) $75.00 for my PLL AM transmitter kit.
The instructions were straightforward and quite educational when building the transmitter in stages and reading the description of exactly what function each stage preformed. Pricy, but educational. Support was always a phone call away. So the investment was well worth the price of the kit from both an education and a recreational standpoint.
Has the idea of bringing these kits back been advanced?
I realize this is an old topic, but if the quality of the kit and instructions remain the same, I would be interested in investing for the children and grandchildren ...not to mention the opportunity to relive a few my younger days through their eyes.