Well in such a configuration, one coupler would be using the neutral of the AC as it's return path, while the other would be using that same neutral of the AC as the injection path, resulting in the 2nd coupler dumping all it's signal right into the return path of the first coupler, and potentially burning up the output toroid, or at the very least over-saturate it to the point it could damage either or both transmitters and couplers.
What is still needed is a way to isolate the two from each other, while allowing each coupler the ability to see the load paths properly onto themselves, and keep them from shoving signal into each other. It would still require a combiner.
But an interesting idea for sure.
RFB
Rather than modify the LPB2-20 Transmitter by designing an oscillator circuit/PLL combination to excite the unit, I have decided to preserve the design as originally intended, especially when finding that the needed crystal is reasonably priced.
Source; International Crystal Manufacturing
http://www.icmfg.com
The PLL circuit we purchased will not go to waste. It will remain attached to the original project for which it was obtained, the Deep Voice LowFER Deep Voice Transmitter, now under development here on this website.
Estimated shipment date is Feb. 22, so this thread will just be dangling around in the meantime.
Well hopefully the crystal you get will be a good frequency to work. Although 1 crystal is not that big of a deal as far as expense, several of them would be, and having just 1 crystal may not be the correct one to work if the frequency chosen doesn't pan out to be workable.
This is why the suggestion of the PLL would be the way to go during the testing phases.
You wont have to modify a thing on that transmitter to use the PLL board. Removing the two IC's and injecting the frequency at the frequency test point or pin 8 of A3's socket isn't exactly modifying the transmitter itself. It is merely substituting the A2 and A3 chips plus the crystal.
When the good frequency is found, simply order a crystal for that frequency, reinstall A2 and A3, install the new crystal and bada bing!
Hopefully the one you already ordered and its final frequency will be workable for your new CC station!
RFB
I ordered crystals for 530 and 570. I am beginning by using the low band, because using any frequency above 830kHz would require a real serious modification of the output filter, and I see those big toroids and realize I am not sure how to design the correct toroids for the mid-band.
Also, looking at the PLL literature that came with the kit, it is all over the place as far as writing is concerned, and does not come through clearly to me. On top of all that, designing an oscillator appropriate to the low AM band is not something my skills have ever dealt with, and at this exact moment I would prefer to postpone a college course until months later.
On the long slow road it would be nice to try the PLL method, and as of now the LowFER transmitter will be the time and place for that.
I am going to run initial tests at 530kHz which is sort of off-band and won't capture much attention. When the result is fine-tuned, I'll move it to 570kHz and call it a win.
If it works poorly I'll be frustrated, but may never try the mid-band, because for all the trouble there is no guarantee it will work better.
Subject to change.
As you guys know, I have been waiting for a CC
transmitter that belongs to me - a good friend
has it. This guy is great and I've known him for
decades. But he is going through a lot right now.
And he lives in another state.
The reality is I may not see this transmitter for a
long time. But I do believe I will eventually get it back.
However, in getting ready for it, like Carl, I have thought
about different frequencies on the AM BCB where i
can eventually transmit. This is an old LPB tube CC rig,
that uses fundamental crystals. There is an inexpensive
source for AM BCB crystals above 1000 kHz so operating
about there would not be a problem.
However, if I decide to go lower in the band - I am stumped.
Do any of you guys know of a manufacturer that will
make a crystal for below 1000 kHz that can withstand
the energy that a tube oscillator would put through it?
I'm not really in any condition to build an crystal oscillator that runs
on a multiple of the frequency which is divided down to the
actual AM BCB channel. At least not right now.
As always, thank you!
Bruce, DOGRADIO STUDIO 2
Hello Bruce:
The people at ICM, International Crystal Manufacturing, have always been very wonderful to talk with. Today I talked with a guy, and although I only ordered two crystals, he spent a calm time talking to me in depth about the subject of crystals.
He is Mark Handley, his number is 800-725-1426 Ext. 265
ICM is familiar with LPB transmitters because they were the OEM supplier for LPB. They may have the exact crystal you need.
Good To Hear From You As Usual!
OK. When I eventually get the transmitter
back, I will call that number.
Thanks very much Carl!
Bruce< DOGRADIO STUDIO 2
Those crystals aren't cheap. But modifying the oscillator to run an LC varactor circuit controlled by a PLL is not that difficult.
I posted some links to excellent reference material on LC and VCO circuits. Those references refer to solid state designs however.
But with a little bit more research..like examining other tube based oscillator circuits, it won't be impossible to convert that RC-6 to work with a PLL.
In fact just recently, a Cunningham 10 watt transmitter was sold on ebay that was modified with a PLL board, replacing the entire oscillator sections. PLL Cunningham
Take a look at the pictures of the unit. You can clearly see the PLL board in place of the oscillator tube section prior to the final tube.
RFB
Gee RFB, that thing looks really great!
I guess I'll look at E-Bay if I get some funds.
I'm going to stop bothering my friend for a
while. If he can't send the RC-6A to me now, I know
there is a good reason. He is very reliable and
sincere.
In the meantime, I'll just keep learning about this stuff.
Thanks again for the info.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
I wish I had the funds to grab that unit during that auction. But every now and then good stuff like that shows up.
My luck its always good deals show up but no funds and when funds are handy, no good deals to be found! Ironic it works out like that a lot! But the patience pays off eventually as Carl discovered. Miracles do happen and when least expected.
With the way things are out there I am sure your friend is pretty tied up just trying to make ends meet. He will get that sent back to you soon. 🙂
RFB
Evidently there is more than one reality.
The one in here, inside the internet building, brings an image signal from AM 1430 while listening to 530 kHz. Since it was "only an image" and therefore not a genuine station, I ordered a 530kHz crystal for carrier current.
But out driving around in the car, that reality has an entirely different 530kHz, one where the Illinois Department of Transportation comes in with a muffled voice giving constructions zones. Although Illinois is 8-miles from here, I have officially abandoned any plans to use 530kHz.
ICM, International Crystal Manufacturing, was very generous and allowed me to change the order to a 670kHz crystal, still within the AM low band.
Continuing my last post, I am beginning to have a grasp of what separates reality # 1 from reality # 2. It is the walls of the house.
If you are inside the walls, that's #1, and outdoors is #2. Why are they so different? It has to do with dB. DeciBels. What are those? Well, one way of describing them is that they are a difference of attenuation.
Huh?
I think RFB will be proud of me, but I now see that out in the car the world is louder, the radio more sensitive, because the walls of the house are gone and are not causing a loss of signal strength coming from all the radio stations. After all, no licensed radio station puts its tower indoors. There is a good reason for that.
Stop. Now we face up to Reality # 3. And that is that no single web posting should go on for too many paragraphs. So I know that I should stop now, and continue this on a future posting. Meet me there.
Isn't being both the teacher and the student fun?!!
I may have to retire early if you keep turning in these excellent thesis posts! 😉
RFB
Teacher and student?
Who?
You or me?
Both?
What have I taught you?
You sure teach me plenty. That's for sure. Why, if I was paying for all this advice it would be too costly. Or would it?
Everyone can be their own teacher as well as their own student.
A good example...when your AMT5K unit arrived. Before breaking out the solder and iron and clippers and screwdriver...you studied the assembly manual to become familiar with the unit's circuitry and theory of operation, identified all the parts and inventoried them, then after all that and once you felt confident enough to proceed with the assembly, began doing just that knowing which way the cathodes of diodes and polarity of electrolytic caps and orientation of DIP IC's and FET's were to be mounted onto the PC board.
You were in effect a teacher and a student.
We all are a teacher and student at some point..no matter what it is we are dealing with...assembling kits, reading information in a book or on the web, or just walking down the street and being aware of what is all around us on a daily basis.
If we were all to just close our minds and never explore or discover and totally depend on something or someone to tell us how to all the time...we would be nothing more than automatons and zombies requiring a punch card program to set our zero's and one's.
Costly? That would depend on a lot of things. But in my view, information is meant to be shared. Knowledge is meant to be spread everywhere and to everyone. To me knowledge is like air, everywhere and available for everyone to take in and continue life.
It is the stingy, the greedy, the selfish, the power hungry that hoard knowledge for themselves because they believe in that other meaning of "Knowledge Is Power"..that other meaning is taken as know more than the other so you have an advantage over them, which is a sick and twisted definition to those three words.
RFB