We Do Not Have Serious Part 15 Research Hobbyists
A "serious part 15 research hobbyist", to my way of thinking, would be someone dedicated to trying all of the transmitter antenna installations that we talk about year after year and providing detailed numbers describing their comparative performance.
We are left with nothing more than opinions and anecdotes about "elevated is better than ground-mount" and "this transmitter does more than that transmitter".
This same problem just came to light in a discussion at the ALPB Forums where we noted that the AMT5000 Transmitter from SSTran has never had an unbiased review nor has it been properly compared to more expensive certified models.
While we drift along the part 15 kits are dying off and becoming ghost stories as most of the kit makers have closed shop.
Important to mention that my comments here pertain to operation in the medium wave band, as part 15 FM has been scientifically and professionally researched by Tim in Bovey with astounding results.
Ground conductivity plays a massive role in our AM setups as well. Stations up north on the coasts will struggle to get out of their own way compared to setups in the midwest.
It seems like over the years we have had several AM Experimentors ranging from ship broadcasts, towers, water towers, homebrew antennas, homebrew rigs... Off the top of my head it seems like Radio8z, Station8, End80, Rich Powers, myself and many more have done various tests with AM.
It seems the top transmitters are always without fail the Rangemaster And Procaster with the Rangemaster slightly favored. SSTran had a good reputation at one time, that is now about completely gone. SSTrans are capable of long distance broadcasts however they require a bit more effort to achieve good results.
Put the antenna loading coil in liquid helium.
Super conductor.
Don't really try to do it though.
I had to say that because some poor
chap might actually try.
Brooce, WUF (?)
Mighty 1650 correctly recalls: "It seems like over the years we have had several AM Experimentors ranging from ship broadcasts, towers, water towers, homebrew antennas, homebrew rigs... Off the top of my head it seems like Radio8z, Station8, End80, Rich Powers, myself and many more have done various tests with AM."
That is 100% true and you can add my name to the list but each of these examples are single events with no comparative dimension... no comparisons were run among different transmitters nor between the range of elevated, ground-mounted, radials, ground rods, with calibrated F.I.M. and laboratory measurements. Basically we've been driving arround in a car looking at range of single transmitter installations.
We're amateur hobbyists dabbling around under sketchy rules with virtually no professionall measuring equipment nor the knowledge to operate it if we had it.
The members we have, including myself, are mainly music or talk programmers with the transmitters being merely a barely understood doorway to the air.
It is concievable that a science-minded member could exist who would tackle all these questions but what I'm pointing out is that we don't happen to have that member.
I strongly encourage folks to make use of the vast amounts of published literature in the ham radio world. There are tons of tech articles about physically small antennas for the 160 meter band. This band is at 1800 - 2000 KHz, just above the AM band. The technical information about 160 meter antennas would be applicable to the top end of the AM band.
Another facet of ham radio that certainly has oodles of info for low-power "broadcasting" are the QRP operators. QRP is shorthand for low-power in the ham world. Google "160 meter qrp antenna" and you'll get lots of starting points to explore.
Mike
AB1AW
Ab1aw said: "I strongly encourage folks to make use of the vast amounts of published literature in the ham radio world."
THAT is a great suggestion!
At last I can escape all this half-informed talk and go somewhere where real technicians live.
Don't take that the right way.
While the suggestion to compare 160m QRP to Part 15 AM is a good one, there is one important difference - there are no antenna restrictions on 160m QRP. And it's the antenna restrictions for Part 15 AM that make it, or more accurately, break it.
To do what Carl is suggesting in his initial post, it would be necessary to own a decent field strength meter. Measuring field strength of different transmitters with identical installations (ground, antenna, etc.) is the only way to do a proper comparison. I also believe that the same transmitters need to also be compared with several different installation scenarios (i.e., different grounding conditions, different locations, etc. as some transmitters might perform better compared to others with poor grounds or better grounds - I believe that was partially the case with the AMT5000 in the AM Transmitter Shootout conducted over at Hobbybroadcaster).
DavidC reminds us: "It's the antenna restrictions for Part 15 AM that make it, or more accurately, break it."
That's a vital point.
And another key factor also mentioned by DavidC is being equipped with a $22k F.I.M. and the needed training to use the meter.
Add to that the cost of aquiring one of each of the leading AM transmitters...
Hobby Bill was able to get some of the manufacturers to lend or give transmitters and one of the never-to-be-forgiven grudges against PhilB is that he chose not to send a sample... which, after all, would have been a kit... a different class compared to the certified pre-built transmitters being subjected to testing.
None of it would amount to anything without the real-estate to set up antenna sites and towers or poles for all the experiments.
By the time it's all figured in it goes beyond hobby and enters the realm of professional laboratory... far more than any part 15 members we've ever known.
to me. I also do QRP anyway.
Sometimes it is easier to experiment with
a ham transmitter instead of a Part 15.219
set-up.
Brooce, Part 15 Hartford
In a previous forum thread on this site I explained how to convert the SStran 3000 to drive a 50 ohm antenna. This would allow one to repurpose a readily available 8 foot mobile ham antenna as a ground mounted AM broadcast antenna. Some folks may find this easier than building a coil and antenna from scratch. It also lets one use or borrow inexpensive equipment like SWR meter to tune the antenna for max performance.
Mike
ab1aw actually had a good idea because there are many apartment antennas that were constructed back in the sixties for the 160 m band and there are articles out there in magazines such as popular Electronics Ham Radio Horizons and quite a few more.
keep in mind that even back in the day Ham Radio keep in mind that even back in the day ham radio operators had the Dilemma of being able to operate an antenna while living in an apartment. Some even lived in dormitories so you know they didn't allow outside antennas but yet they were able to perform with a relatively short antenna.
Different constructions could be experimented with as well such as J poles and other types of antenna constructions like the helical antenna. I do think that in order for hobby radio to really go anywhere is for people to get their minds out of that one sentence thing that keeps on coming up all the time. Think out of the box and look at some earlier articles I'm sure somewhere you can find some older magazines laying around that some hams might have. Ask questions to some of your ham buddies and see what happens you never know you might come up with a really great antenna that gets some serious range and yet still be compliant for part 15 AM
ab1aw Said:
In a previous forum thread on this site I explained how to convert the SStran 3000 to drive a 50 ohm antenna.
MrBruce Said:
I have posted numorous posts with schmatic diagrams asking about the antenna impedance of the Chris Cuff C-Quam AM Stereo Transmitter kit, but to no avail has anyone answered my questions.
I realize most people want me to simply use a 10 foot wire antenna and that be it, but, with a nano watt output there has to be some suggestions in regards to making this thing go past a nano watt and the other defect is when you turn the power pot up to a certain level, the audio is totally squashed and none-existant, Chris Cuff's answer is turn the power pot back a notch, but with a nano watt or less you are not seeing any distance past 20 feet if you are lucky maybe 20 feet to a good radio! That is if the kit is built per his instructions and my C-Quam transmitter was built by Chris Cuff himself not me or anyone else.
Now I've seen mods done to the Chris Cuff C-Quam Stereo transmitter that use amplifers of some type, but people are not willing to share exactly what we see in some published photos on the web.
I mean even carrier current can be used if the amplifer is putting out more than a 100 Milliwatts, but the amplifer in most cases is 50 Ohms input and output impedence and we have not figured out the impedence of the Chris Cuff transmitter to match to an input of 50 Ohms.
I have asked how this transmitter can be altered to achieve a 50 Ohm output to match a 50 Ohm impedence amplifer, even to achieve a 100 milliwatt output to an antenna or carrier current using a higher powered linear amplifer at maybe 1 watt.
Of course the amplifer has to be geared for the MW band at 1MHz (1000 KHz) and above for it to work.
I am not looking for advice on how to make an illegal transmitter, but at a nano watt or less come on, something has to be suggested that will allow both positive and negative audio peaks at 100 milliwatts total output before the antenna.
Again I post the schematic diagram of the final stage of the Chris Cuff C-Quam Transmitter to this thread, when will someone look at it and seriously post the actual impedence output and what needs to be done to make this thing operate at least at a legal part 15 level?
A simple 10 foot antenna does not acheive any usable distance other than a table top transmitter to table top radio novelty. It has decent C-Quam stereo sound, it just needs a little engineering help to achieve what other part 15 AM transmitters achieve.
Click link below for the schematic diagram of the final RF output stage of the Chris Cuff C-Quam Stereo Transmitter.
NOTICE: IN THIS SCHEMATIC BELOW THERE ARE TWO 390 Ohm RESISTORS SHOWING NEAR THOSE TWO 2N3904 TRANSISTORS . THOSE ARE ERRORS ON THE PUBLISHED SCHEMATIC DIAGRAM ON PART15.US. THOSE ARE ACTUALLY 3.9K Ohm RESISTORS, NOT 390 Ohms!! That is a typo in the schematic diagram!!
Please take note of that while examining that schematic diagram at the link below this notice.
Other Schematic diagrams for the Chris Cuff C-Quam Stereo Transmitter:
Thanks for reading...
Bruce.
The short story:
On sheet 6 of 6 of the schematic: Ignore/remove the components of the RF power amp stage. At point E (top right of schematic) connect a 1500pF capacitor (C1) to ground. Also at point E connect one end of a 20 uH coil. Connect the other end of the coil to one end of a 0.005 uF capacitor (C2). Connect the other end of that capacitor (C2) to ground. Connect your 50 ohm antenna across capacitor C2.
The long story:
The RF "preamp" stage (with the 2N3904 and 2N3906 transistors) is a class AB push-pull amplifier. This type of amplifier is essentially a symmetrical pair of common collector (aka emitter follower) amplifiers. In this configuration the theorectical max efficiency is about 78%. The output "resistance" of this type of amplifier is whatever the load resistance you choose - within the power handling limits of the transistors. The current gain is the Beta of the transistors. The voltage gain is unity (i.e. voltage in = voltage out). With a 9 volt power supply driving a 900 ohm load we get 90 millwatts output. The additional components I described above create a Pi-network to convert the 900 ohm output to drive a 50 ohm antenna.
The two transistors (2N3904 and 2N3906) are going to get hot. I suggest adding heat sinks to them. I suspect that these transistors are the little plastic cases with one flat side (TO-92). There are slip-on heat sinks available for them.
I hope that helps.
Mike
ab1aw Said:
On sheet 6 of 6 of the schematic: Ignore/remove the components of the RF power amp stage. At point E (top right of schematic) connect a 1500pF capacitor (C1) to ground. Also at point E connect one end of a 20 uH coil. Connect the other end of the coil to one end of a 0.005 uF capacitor (C2). Connect the other end of that capacitor (C2) to ground. Connect your 50 ohm antenna across capacitor C2.
MrBruce Said:
First off thanks for the reply!!
I seen it a few days ago, but wanted to wait until I had more time available to think out my reply.
The schematic diagrams for the Chris Cuff Transmitter published here at part15.us were designed by Station8 (Jeff) according to proof reading done by Chris Cuff as they were designed. So credit goes to both Station8 and Chris Cuff.
Errors were caught after I published the original schematics at part15.us, but they are far more superior as to compared by various rough draft hand drawn ones originally done by Chris Cuff.
One thing I noticed was no parts were given a specific part number in the schematic diagram, such as R1, C1, D1 or L1 which would have been great for parts discription and better explanation for parts placement.
Station8 used TinyCAD to make those diagrams, but his time limitations prevented him from improving the schematic diagram design even futher.
So Mike ab1aw I have to ask 2 questions in regards to your directions you posted above.
Which side of C-1 would I connect the antenna to? You said: "Also at point E connect one end of a 20 uH coil. Connect the other end of the coil to one end of a 0.005 uF capacitor (C2). Connect the other end of that capacitor (C2) to ground. Connect your 50 ohm antenna across capacitor C2."
Which side of C2 would I connect the antenna to? You said across capacitor C2, obviously C2 has only two terminals, one to ground and the other to the 20 uH coil. So obviously you mean connect the antenna between the coil and C2 correct?
Also, a 20 uH coil, can you please point me to a good example on the web of such a coil? Are they already factory made or do I have to make such a coil and of what parts?
Looking at the RF Power Amp Stage (the bottom part of the schematic) if using that 150pF capacitor and using a 2N3053 transistor or any of the ones the schematic diagram states were used, what exactly is the potential output with that set up? Or does any part of that design actually make things worse?
If it was possible to replace the publish page 6 of the schematic diagram with a better updated copy, I would do that, but I can not personally edit anything already published to part15.us or edit the links without starting a whole new topic in my name with all new links.
Bruce.
Hey, Carl- one of the fellows in STL that runs a ham repeater has a pro meter for broadcasting. Shoot me an email if you're interested in chatting with him.