EDIT TO ADD: Apr. 17 2011. See my post later in this thread about the efficiency breakthrough.
END EDIT
EDIT TO ADD: Apr. 17 2011. See my post later in this thread about the efficiency breakthrough.
END EDIT
In another thread (http://www.part15.us/node/2714) I reported on my efforts to increase the efficiency of the Ramsey AM-25 transmitter. Subsequently, since I am reluctant to use my Ramsey or SSTRAN outdoors, I was inspired to construct a transmitter based on my study which could be mounted in a watertight enclosure for outdoor use and I would like to share the project here. This is not meant to be a builder’s guide but rather to show (and show off) what I did in case it may inspire others to develop a similar or improved project.
The first picture attached below shows the assembled transmitter board and the second picure illustrates how it mounts in a standard 4″x4″ marine watertight electrical enclosure.
The transmitter is divided into three sections: audio modulator/bias, oscillator, and RF final amplifier/filter. The audio section is very similar to the Ramsey AM-25 design which provides adjustable audio gain and DC bias to the final. The oscillator is crystal based and uses a digital IC to produce the drive for the final. The final amplifier is a BJT based circuit with a 5 pole low pass filter. Provision has been made for an RF isolation/impedance matching transformer which is yet to be installed on the PC board. This transformer will provide isolation between the circuit ground and antenna system ground to prevent ground loops.
The circuit was built on a PC board using a modified “dead bug” technique. All components are surface mounted to the board which allows a continuous ground plane on the back side. This method also makes circuit changes very simple for further experimentation. The PC board was made using the “toner transfer” method and was etched in ferric chloride. The board will be coated with clear lacquer prior to use to prevent oxidation of the copper traces. I hand tinned some of the traces and then decided this was not worth the effort.
The transmitter checks out with an efficiency of 65% and modulation up to 95% without noticeable distortion. The frequency is stable to +/-2 Hz from cold start to warm but I have yet to check this at the expected ambient temperature extremes so this is still a work in progress. My intent is to mount this at the base of a yet to be built base coil loaded outdoor antenna so details about cable connections have yet to be determined. My plan is to feed a differential audio line level signal, DC power, and ground via a multi conductor cable. I intend to report here when the installation and testing are completed, probably in the next few months.
My well stocked junk box meant I had to buy only the two toroid cores for the filter and the enclosure. It is satisfying to stir a pile of parts with a soldering iron and end up with something which works and then share the experience with others who understand it.
Neil
rock95seven says
Awesome Homebrew
Awesome Homebrew and you don’t have to worry about getting drunk off of it either. lol
That is a great looking transmitter and i can’t wait to see how well it performs once it has a load on it. Keep us posted and have fun, although from the looks of it you have enjoyed the build very much so far.
Until next time, keep on rockin’
Ken Norris says
Cool homebrew
I’m jealous of your skills! ๐
That said, many folks mount their SSTRANs in weatherproof boxes without problems, so my question is: What prompted you to avoid it?
RichPowers says
It does look impressive Niel!
It does look impressive Niel! Can’t wait for the completed project in action. Seems very cool!
Ken Norris says
Integrated TX system
I like the idea of an integrated TX system, rather like the Rangemaster, but with a loading coil. Next shot for me will be a ground-mounted similar idea, unless I can relocate the formulas for building my mag-loop experiment.
I almost tried it with the Spitfire TX. Idea was to mount it inside the same PVC pipe with the coil wound on it (above the TX location in the pipe) and an older Shakespeare marine antenna (which may or may not have a tuned length core inside). It was to be a very clean installation, but I couldn’t get enough modulation and range out of the Spitfire compared to the TH TX I’m using now.
I think the SSTRAN will show better performance and would be worth the effort.
Carl Blare says
Not Sure
Ken, I’m not sure if you meant that the xmtr circuit card would actually be fit within the coil, but if so, what would that do to either the coil performance or the xmtr performance?
radio8z says
Thanks
Thanks for the kind comments. The toner transfer for the PC board got ugly but after 8 tries I got it to work. All the guides I read urged too high temp and too much pressure. I backed off on both and it worked.
Ken asked “That said, many folks mount their SSTRANs in weatherproof boxes without problems, so my question is: What prompted you to avoid it?” The SSTRAN is just too pretty to put outdoors but that would work. The real reason is that I know that this tx. will drive a base coil loaded antenna with at least 65 mW (with 100 mW input) and I don’t know about the SSTRAN power drive capability. Also, I have spare parts in case of lightning damage and can repair it quickly due to the modified dead bug construction.
It checked out on my loaded indoor antenna but it will be a while before I get to try it outdoors.
Neil
scwis says
65% efficiency is pretty exciting!!!
I’d say Neil has really brought something new and exciting to the table here. Should we all start begging for a foil pattern and parts list?
I would definitely be willing to pay for a kit with the PC board and parts list, that’s for sure ๐
How about a version with the modulator in the studio and the exciter on the mast?
Nice product!
Ken Norris says
Nice product!
Indeed …
“Should we all start begging for a foil pattern and parts list?”
(Holes in knees ;)) … Where do I sign up?
Ken Norris says
RE: Not Sure
I said: “mount it inside the same PVC pipe with the coil wound on it (above the TX location in the pipe)”
IOW, inside a PVC pipe, the TX at the bottom (base mount point) of the pipe, then above that the coil windings, and finally, above the PVC pipe, the antenna mount and antenna.
Oh, and P.S., now I’m thinking about a larger diameter pipe with a cage system. All the cage systems I’ve seen are too flimsy, even for testing here this time of year… winds were up to about 30mph today. I get PVC really cheap at the local recycle yard, so stringing wire on one is no big deal, certainly not considering I will wind a coil on it as well.
scwis says
That brings to mind a nice image
With a 6″ pipe ten feet long you could put the cage and the coil on the same pipe.
If you added a short section on the bottom a there would be a little spot for a small transmitter too.
Again, this image is not to scale and twelve verticals would probably work fine.
A 12″ pipe would only need 13 turns on the coil with the 50 Ohm tap two turns from the bottom. Plenty of room for the transmitter in the bottom, too.
Lay out some ground radials and put some fire to the wire ๐
Carl Blare says
Do You Realize
SCWIS, do you realize your illustration shows a completely self-contained transmitter/antenna in-a tube? A very significant product for the part 15 market. Get patents!
RichPowers says
SCWIS, do you realize your
SCWIS, do you realize your illustration shows a completely self-contained transmitter/antenna in-a tube? A very significant product for the part 15 market. Get patents!
Well, I believe that is exactly Ken had described.. but illustrations do speak louder than words!
MICRO1700 says
WOW you guys have really got something!!
SCWIS – I’m not sure what kind of
pipe you are talking about. Did I
miss something?
And Neil – what is the output
impedance of your prototype
transmitter? I’m assuming you are
aiming for around 50 ohms.
This is exciting!
Bruce,
MICRO1690/1700
scwis says
Referring to Bruce’s question
That was PVC pipe from the comment Ken submitted where he said he could get PVC pipe cheap at a local recycling yard.
It also refers to the cage antenna concept discussed in this thread
part15.us/node/2785#comment-12561
Ken Norris says
Images
How do you do it? For the life of me I can’t include an image. When I try I always get a message telling me it can’t scale the original image … no matter if it’s small and only 16kb.
What am I am I missing? Can someone please walk me through it step-by-step?
TIA …
radio8z says
AM Transmitter Update
This is still a work in progress and that makes me reluctant to publish construction details at this time. .
For example, a simulation predicted that a change in the filter can boost efficiency by 10% and I confirmed this on my prototyping board but not with the transmitter I built.
Bruce asked about the output impedance. I have been testing the unit at 50 and 29 ohms. A base coil loaded antenna will have an impedance around 20 to 30 ohms which will drop the efficiency and I am trying to optimize the circuit for this load. I have tested a matching transformer but the loss is higher than I want so I am working on a filter stage which will also match the impedances without a transformer hoping to gain efficiency. What I have already works but I think it can work better with a few changes.
More to come.
By the way, the single pipe idea for the whole system is intriguing. Good thinking!
Neil
Ken Norris says
Coil at bottom
Howdy …
“A 12″ pipe would only need 13 turns on the coil with the 50 Ohm tap two turns from the bottom. Plenty of room for the transmitter in the bottom, too.”
Could you explain how this was modeled? IOW, where did the number of coil turns and tap turns come from?
What would happen if the the coil was top- or mid- mounted?
scwis says
How this was modeled
I started with this pamphlet and used the formulas starting on page 4 of Medium Frequency Antenna Construction Plans
Then I made a little Excel spreadsheet so I could try different configurations without using the old pencil-paper-scientific calculator method and showing my work for extra credit ๐ A copy of the spreadsheet can be downloaded here Antennacalc.xls
I can testify to the efficacy of the formulas in the plans pamphlet. I have used both air and iron powder core (rod and toroid) coils made using these formulas with great success.
MICRO1700 says
Thank you
Thank you SCWIS for the answer about
the pipe and for the large print, I appreciate
it.
And Neil, thanks for the answer regarding
the output impedance of your prototype.
I am lucky – I came upon access to a Mac
computer that I can use sometimes, and
now I can read the board again. I can now
magnify greatly, make the cursor larger,
and invert the video (which really helps.) So
you guys don’t have to enlarge the print
messages you are sending.
However, the info regarding the PC is greatly
appreciated, because I have 2 PCs at home,
and I am going to try everything you guys
have talked about.
These new ideas, Neil’s transmitter design,
the cage antenna, and the whole works in
one big tube are fantastic – we really have
something going here.
Great stuff!
Bruce,
MICRO1690/1700
MICRO1700 says
Cage Antenna: How about this…
I have a bunch of PVC pipe and copper
tubes lying around.
How about a ten foot high PVC pipe with
a ten foot copper tube on the front, the
left, the back, and on the right side.
In other words, one copper tube every
90 degrees around the PVC pipe? I guess
they would be tie wrapped on or something
like that. It would probably have to be guyed.
My SS-Tran would go into an upside down
wastebasket mounted on the bottom of the
PVC tube, along with the coil, which would
be wound on the PVC tube.
Have we hit the point of diminishing returns
here?
Best Wishes,
Bruce, MICRO1690/1700
Carl Blare says
Part 15 Is That Point
Bruce you walked right into this one.
Part 15 broadcasting IS the point of diminishing returns.
MICRO1700 says
Yes it is…
But I love experimenting with the
electronics, and it reminds me of
when I was growing up.
So to me, the diminishing returns
don’t matter.
Best Wishes, Carl…
Bruce,
MICRO1690/1700
RichPowers says
Bruce, I remember living in
Bruce, I remember living in Englewood Colo. when I was in about the 5th grade.
At home I had a “CB Base Station” It was just a plastic toy, and I can’t remember the brand, but it looked real neat… It really was only good for talking to other toy walkie talkies while in the neighbor hood.
But one time after wrapping a wire around my whip and out the window up on the roof and concocted a outdoor antenna with several coat hangers and aluminum foil.. I had no idea what I was doing, but was thrilled to find I was able to talk to a trucker for about 4 or 5 minutes!
It was just a one time occurrence, but it was cool!
MICRO1700 says
Hi Rich!
Well. from my point of view you hit
the nail right on the head! And good
going with that CB antenna you made!
I started with CB and listening to far
away AM radio stations. This lead to
other radio stuff.
But one of the funniest things that ever
happened on CB went like this:
My best friend lived in the house behind
mine. He was on the street behind my
street and our back yards faced each other.
The gap between our houses was about
150 feet. Our Space Patrol walkie talkies
would not make that distance, so we couldn’t
even talk between houses! Then we put up
a 150 foot thin copper wire that ran from his
bedroom window to mine. Then we could talk!
If his or my CB was hooked to the wire it worked.
Both of them connected on either end was fine, too.
Those were the days. but thanks to my Part 15 stuff
and a bunch of other radio projects, those days are
still here (sort of.) I think that we like experimenting
with Part 15 AM BCB transmission because we really
don’t always know what will happen, and that’s the
fun part!
Best Wishes,
Bruce, MICRO1690/1700
Carl Blare says
Sorcerers of Radio
The term “sorcerers of radio” just got said on the Geoff Filipiak Show just when I needed it, so I will use it now to describe what you guys are talking about. Here’s what I realize after reflecting for one-second on your comments: if the world had developed low power to its full potential, they would never have needed high power to overcome the shortcomings of cheaply manufactured radio receivers. NO, STAND BACK! LET ME TALK! If low power were the norm, today we would enjoy many more radio stations and the cancer rate would be a whole lot lower. Why? What do you mean “why.” Isn’t it obvious? TAKE YOUR HANDS OFF OF ME. See that spot on your skin? That’s from the high power radiation which is cooking everybody. WHAT’S THE HOOD FOR?
This has been a dramatization. Any resemblance is unintentional.
MICRO1700 says
Carl I can be just as silly as you are!
HE PLUGGED IN THE A.C. OULET TO SEE
WHAT WOULD HAPPEN!
BAMM!
“This also has been a dramatization.”
Now we’ll just have to see how Neil’s new
transmitter circuit works when he has it
ready.
Bruce,
MICRO1690/1700
Carl Blare says
Too Much Fun
Bruce, that happened to me way in past. My mom’s iron had a broken cord and they kept the AC plug with all the gnarled wires, so I figured that I would plug it in the wall. Fire flew four feet into the room and the entire house went black.
Neil’s transmitter is yet to come.
radio8z says
Efficiency Breakthrough…86.7% with 100 mW Input
As I mentioned before this transmitter is a work in progress. Through simulations I was able to develop an output network which simulated to 88.7% efficiency and I built it and measured the following data:
DC Power in 99.4 mW
RF Power out 86.2 mW into a 50 ohm load.
Measured Efficiency = 86.7%.
Driving a 29 ohm resistive load which is closer to what a base loaded antenna will present gave a measured efficiency of 83.9%.
This is about as good as it gets!
A major change was using a 3 pole filter instead of the original 5 pole filter on the output. This doesn’t give as good harmonic suppression but it is within the FCC limits according to the simulation. I just simulated the changes using a 5 pole filter and the calculated efficiency is 84%. If the simulation model works as well as the 3 pole model did then this is encouraging. I’ll report when I make the changes and do an actual measurement on the 5 pole design.
Neil
scwis says
Amazing news
I was over the moon at 65%, anything over 80% would be too much to hope for. Really remarkable news!
As far as range goes, RF power attenuates as a logarithmic function so merely doubling range requires a four-fold increase in power.
It’s beginning to look like Neil will at least get a three fold increase in power over many of the units available today, which might get us range X 1.3
More important in my mind is that the receivers within range will perform much better with the higher output. Even a cheap pocket radio ought to open up to a signal that strong.
radio8z says
More Data
The measured efficiency of the tx. using the 5 pole filter is 80% with a 50 ohm load. I am arguing with myself about whether to use a 5 pole or 3 pole filter. There’s not a lot of range difference between 80 and 86% but why not go 86 if it can be done? The simulated harmonic suppression is adequate for both filters. The 3 pole simulates at -36 dBc and the 5 pole at -63 dBc and a resonant base loaded antenna will give even more suppression. I need to do some more testing before I decide which to go with since there might be some “gotchas” I haven’t found yet.
Regarding the range increase, it could be better than SCWIS mentioned. If a typical AM tx. efficiency is 30 percent (just a guess, some may be and probably are higher) then the power ratio is 86/30 = 2.87. The field strength is proportional to the square root of the power so for a given field strength the range will increase by SQRT(2.87) = 1.69. Without knowing the actual efficiency or power output of other transmitters it is not possible to predict this but if the power/efficiency is known it can be done as illustrated.
Neil
Carl Blare says
Considerations
Another triumph for part15.us, having an exceptionally efficient transmitter designed here.
A career opener for you, Neil, as to whether you might become either an equipment supplier or perhaps make a patent agreement for someone else to manufacture and offer the product.
Somewhat switching focus, earlier SCWIS drew a cage monopole in a tube, and I question the apparent connecting of the several elements at the top, as shown in the illustration. My gut says the top of each element should end unconnected.
In the unconnected state, again adding another idea, there could be several top hats, one for each element.
I hope these points stimulate a discussion.