Now that I’m happy with the audio performance of my SSTran, I’m going to start working on modifications in earnest! NOTE: None of these modifications will affect the input power to the final stage!
Now that I’m happy with the audio performance of my SSTran, I’m going to start working on modifications in earnest! NOTE: None of these modifications will affect the input power to the final stage!
In the works:
1. Frequency adjust trimmer to allow the carrier frequency to be set precisely on channel.
2. Improved output match efficiency using a large iron-core toroid instead of the small axial-lead inductors. I just ordered up some #15 material toriods from Amidon Associates. The toroid should still fit inside the enclosure.
Planned:
1. On/Off switch
2. Remote metering for the output
3. External access to the output trimmer capacitor
4. Reduced adjustment range for the Compression pot to limit it to 1:1 – 2:1 and make it easier to choose low compression ratios
5. Negative peak LED to indicate when the carrier is being modulated at -95% or greater
I’ll let you know how it turns out!
Meanwhile, I have to say that I don’t agree that Part 15 AM can’t be used for high fidelity transmission. My SSTran sounds great on classical music now, and so does my Rangemaster. Listening on a high quality AM radio is an amazing experience! The SSTran signal is plenty strong enough to give excellent reception anywhere on my property, and the Rangemaster pushes that out to a couple of blocks. Sure, as you get further away, the audio quality drops due to noise, co-channel interference, etc. but it still sounds good and these impairments do not really spoil the enjoyment of the music until the signal gets very weak.
I have been a longtime devoted listener to classical music on AM over CBC Radio One (until they took it off the air last year) from CBL-Toronto (now off the air) and CBW-Winnipeg. AM radio is very usable for classical music, especially if you’re actually interested in the music and not just listening to the equipment. There’s a commercial classical AM station in Kansas City, KXTR (1660) that I hear from time to time. So it definitely can be done!
Part 15 is, in fact, a great place to experiment with high quality AM because we aren’t forced into a need to over-process the signal in an attempt to be louder than everyone else on the dial. Don’t get me wrong, though– some processing is good, and if someone offered me a used Inovonics 222 at a good price, I would probably be inclined to pick it up!
SSTRAN mods
WEAK,
I have enjoyed your writeups about the SSTRAN. Thought you might be interested in this:
http://part15.us/node/1366
I also installed a “netting” trimmer cap (3-12 pf) across C12 and can net the frequency to within a Hz or two. My unit is indoors and at a pretty constant temperature and the frequency easily stays within +/- 10 Hz over the long term.
Neil
Great ideas!
I am planning to use a similar technique to zero the transmitter frequency. I think that actually, a butterfly trimmer would be ideal, but they are too big and too hard to find these days– so I’ll probably just put a trimmer across one of the fixed caps.
As for the output matching, I’m not really planning on changing the overall design at this point– just reducing the losses by changing to a large diameter iron toroid inductor. I’m also thinking about various simple ways of getting rid of that output trimmer that shunts some of the signal to ground. Essentially, you’ve got a capacitive divider there– the RF current that flows through the cap doesn’t go to the antenna. That’s why the manual recommends to choose the inductor setting that results in using the lowest capacitance to tune for resonance.
WEAK-AM
Classical Music and More!
More thoughts SSTRAN
WEAK,
I realized after I posted that you had engaged in the link I provided and already had seen it. Oh well, maybe others will be interested.
My frequency was a bit high so paralleling the trimmer cap with C12 worked. As you probably know, you may have to make the fixed cap a bit smaller to get the adjustment range you need. My experience is that this is set and forget unless you want to continually adjust it for DNO (dead nuts on….a technical term) frequency all the time.
Regarding the output Z, PhilB contributed to a long thread where this was discussed and explained how the output network works. I believe I also posted a math analysis of this. Try a search and if you can’t find it, let me know here and I will try to dig it up. I just don’t remember the specific topic that was being discussed so it may take a bit of time to find it.
Neil
I always enjoy your comments!
Neil,
I always enjoy reading your suggestions! Thanks for the tips on your frequency adjustment! I think being within a few Hz will be satisfactory. BTW my Rangemaster has remained within about 1-2 Hz of the co-channel commercial station for about 3 months now, mounted outside and operated in all kinds of weather and temperature variations. Remarkable! Being on channel makes a difference in usable range.
Yes, I’ve crawled through all of the discussions on the output circuit. There are basically only two sources of loss in the existing circuit. Loss in the inductors (those are not very high Q components) and loss due to the capacitive divider. I plan to address the loss in the inductors by going to a large toroid. The capacitive divider will be the impetus for further experimentation.
WEAK-AM
Classical Music and More!
Classical on AM
Hi WEAK,
Just curious…are you in the Buffalo, NY area by any chance? I used to listen to those stations as well. (CHWO, AM 740, still sounds good to me.)
I am running an SStran with the base loaded vertical and external processing.
[email protected]
CHWO is a great station!
Although I do miss CBL… though not as much, now that they took all of the classical programming and many of the other programs I enjoyed off the air.
I can no longer listen to CHWO due to IBOC interference from WGN. I just hate the IBOC system! It creates so much noise and interference to first and second adjacent stations! Even the host station sounds bad! I just wrote WGN a letter complaining about the interference, partly motivated by statements in Radio World that there haven’t been many complaints. I’m going to make sure that some get on the record!
I’m in the midwest– primarily in northern Illinois, but I also have a location in southern MI.
What kind of range are you getting with your setup and did you install any radials? I would love to hear more about your system.
I take it that you are broadcasting classical music? I have the compression turned all the way down on my SSTran. It sounds fantastic!
WEAK-AM
Classical Music and More!
My humble set-up
Hi WEAK,
Sorry, no I’m not running classical music…(Although professionally I announce at a classical station) I am running alternative talk. Some RBN, some truthnetradio.com and the show “News And Views” from the Information Radio Network 1 to 3 each weekday afternoon. Processing is a yamaha (rack mount) compresser / limiter / gate into a 12 band per channel EQ for audio quality and bandwidth limiting. 24-9 foot radials help get the signal out, however, the range changes with the weather. For the last 3 to 4 months the temperature has fluctuated from the 20’s to the upper 40’s with a mixed bag of precipitation. I have had to retune for 13 volts twice now. For the last few days it has been below freezing so the signal gets out about 3/4 of a mile. When the temp. rises and it rains, it gets out about 1/2 mile. (I’m not exactly happy about this!)
As far as IBOC: On AM it is a complete waste of money and energy. The mess that the AM band has become has been made worse by digital hash. Right now, less than two dozen stations are still running the “buzzsaw” at night. In my opinion, if the FCC cares so little for the AM band…let those of us who would like to preserve it run 10 watts at the high end. We’ll abide by the rules in effect now and with enough of us, maybe there will be some decent programming people will want to listen to.
Sorry about the rant…
[email protected]
Toroid Material Selection
PhilB pointed out to me that according to his tests, the #15 iron powder material is not efficient for use at AM radio frequencies (at least not at the upper end of the band). He recommended #2 material instead.
The downside of this is that #2 has a lower permeability– 10 instead of 25– meaning that you need more turns of wire to achieve a given inductance value. A further consequence is the need for a larger sized core (to accommodate the additional turns). 🙁
I just thought I should pass along this information in case any of you are interested in experimenting with these toroids. Stay tuned– I will present my findings in a couple of weeks after I receive my order from Amidon and wind up my new output coil.
WEAK-AM
Classical Music and More!
Rants on IBOC are welcome!
I am actually thinking of posting a slightly edited version of my WGN letter for the benefit of others here who might be inspired to write a letter of complaint to their favorite interference causing IBOC station. Last summer I told you folks that IBOC would become a problem for LPAM operation, and wouldn’t you know, it has! DUH! There are quite a few channels in my area that I cannot use because they are DESTROYED by IBOC hash. Not to mention the other stations down the dial that I would LIKE to be able to listen to (like CHWO), but CAN”T because of the gosh darned IBOC noise!!
Anyway, brief diversion over, I snooped around and think I have found your picture on the WNED (classical 94.5) web site. You are one of the program hosts. I think I know which one. Tell me if I am right, and I’ll send you a message to your e-mail at the station.
I am just nuts about classical radio, and I support (meaning $$) a total of THREE stations, two in IL and one in MI.
I appreciate your description of your station. Mine is still very experimental; I am tweaking and improving things as I go along. I wish I had more room for a better antenna setup. Of course right now is not a good time to be working outdoors… brrr!
WEAK-AM
Classical Music and More!
IBOC and more…
WNED is correct, sir! So e-mail away.
Did you know… about a month after the nighttime IBAC (In Band, Adjacent Channel) was foisted on the listening public, Citadel told their AM’s to cease operation at night! Why? because WJR in Detroit was interfering with WABC in New York…and vise-versa. The noise was present within both stations’ protected contours. What? iBiquity didn’t know this would happen? Where is the FCC? Their job is to prevent interference not cause it!
[email protected]
New “Tubes” for the final!
All this talk about keeping the output voltage of the SSTran under a certain value got me to thinking. Why should that be? I may be wrong, but it sounds to me like there is an underlying problem that needs investigation.
The PN2222A transistors used in the output stage of the SSTran are nice devices, but they only have a 40V breakdown. That’s not much headroom if you get a significant amount of RF voltage flying around in the collector circuit. So I decided to have a look at what else is out there that might be a reasonable drop-in. Just like in the “old days”, when we’d go looking for the “industrial version” of a particular tube to get a little better performance.
I found two devices so far that seem like they might work. Both are available from Digi-Key. The first is the MPS-A06. This transistor has a Vceo of 80V vs. 40V for the PN2222A. It also has a similar hfe of 100 minimum at Ic=10 mA . The output capacitance does not appear excessive; it is 7 pF at 10V. So this could be a good one to try.
The second device is the 2SC2632. This appears to be a slightly updated version of the 2SC2631. It is a silicon epitaxial planar device, intended for low-frequency high breakdown voltage amplification. The Vceo of this transistor is 150V, which is almost 4x that of the PN2222A. It has a minimum hfe of 130 at Ic=10 mA. And the output capacitance is 3 pF at 10V. This could be a hot prospect!
These two devices appear to be somewhat unique. Low power devices typically have low breakdown voltages. Medium and high power devices have higher breakdown voltages, but these often come at the expense of lower gain, and higher input and output capacitance. Thus, they would not necessarily be “drop-in” replacements.
I am going to order some of each of these and give them a try. I’m curious to know if anyone else has experimented with “new finals” for their SSTran! This highlights another good thing about kits– they’re great for modifying!
WEAK-AM
Classical Music and More!
The new “tubes” thing
Now there is an idea I had not thought of…replacing the 2N2222. Would you please let us know what you find?
BTW: I have added remote metering and power control. I have a three-pair shielded cable for audio and another for the remotes. The second cable connects to an interface in the garage that houses a 12 volt DC supply and a general purpose relay for x-mitter power so I can switch it on and off or meter the stick from inside my studio or out back. Maybe one of these days I can post some photos.
So far, no e-mail from you………….
[email protected]
MPS-A06
hi,
Have you made the try with those MPS-A06 ?
Any improvement ?
Thanks
Different transistors?
Hi,
If I understand your post, you are probably asking for an update from an earlier post by WEAK regarding trying different transistors. I would also be interested in his report.
But, a well design circuit such as the output stage of the AMT3000 operates in a manner which is mostly independent of the active devices (transistors) with biasing, gain, and overall performance being set by the passive components (resistors and capacitors) as long as the transistors meet minimum specifications. I would not predict any advantage will be gained by substitution of transistors different from those specified by the kit provider.
I could be proven wrong, but this is my take on the subject.
Neil
I don’t recommend changing the transistors
I did not notice much of a difference using other transistors in the output of the SSTRAN. For those that haven’t been following the thread, I tested a few other devices with higher collector voltage ratings that were compatible with the circuit. All of them worked fine, but I did not notice much of a difference in audio distortion or stability under conditions of mis-tuning.
In particular, the audio distortion problem noted by some, and mentioned in the adjustment procedure for the external antenna, seems primarily due to a tendency toward instability when the output load impedance is too far from the design value. By adjusting the output trimmer until the rectified antenna voltage is under 13V, you are essentially bringing the load impedance into an acceptable range.
There are basically two ways to keep the output stage stable and reduce the possibility of audio distortion: one is to install a resistor in the output tank (the kit uses a value of 820 ohms for lower frequencies), and the other is to adjust the output loading (trimmer) capacitor. Although the resistor wastes some power, I personally prefer that approach because it ensures that there is at least some resistive loading on the output at all times. Note that you may be able to use a higher value than 820 ohms depending upon your particular load impedance. I found experimentally that values of up to 5 kilohms could help stabilize the output and reduce or eliminate the distortion problem. I finally chose a value of 3.3K and left that in permanently. You should not hear distortion if the transmitter is adjusted properly (including setting the audio levels correctly). The best way to see exactly what is going on is to monitor the RF signal with a high frequency oscilloscope. This will show you what modulation depth you are achieving, and you will also be able to see if the output is tuned correctly.
I do agree that if you have a very efficient (high Q) antenna system, it is possible to reach a point where the audio high frequency response will be affected. I think this is highly unlikely for the vast majority of installations, even if you use a high Q loading coil (which is desirable), because ground losses will still tend to limit the Q of the antenna system. If you are blessed with a situation where you are able to deploy a very low loss ground system and you also use a highly efficient loading coil, it could affect the audio. However this should not manifest itself as “distorted sound” in the usual sense, but rather as a reduction in high frequency response.
WEAK-AM
Classical Music and More!
“New tubes”
I’m using the Wenzel ckt, which I understand is the SStran basic ckt, and using a SStran type antenna. Since I’ve attached a high Q loading coil, the modulation sounds raucously clipped.
It didn’t occur to me that the transistors may be saturated or to lower the voltage, which I’ll try. I do plan to install a capacitance hat, that may reduce the Q enough for me to see if that’s affecting the sound.
Anyone else had this problem or know what’s going on?
Macrohenry
SSTRAN audio clipping
See this thread:
http://part15.us/node/1641
Neil