I must say I agree that knowledge belongs to the public domain.
The idea of private knowledge seems anti-social.
From inside the house 570 and 970 seem like good carrier current frequencies because they are mostly blank all the time.
Outside driving around in the car there is no such thing as a blank frequency. There are stations on every channel.
Aha, but the strength of carrier current is that it delivers the signal right into people's homes via the power wires, thereby by-passing all that outdoor band clutter.
Home run and touchdown!
"Aha, but the strength of carrier current is that it delivers the signal right into people's homes via the power wires, thereby by-passing all that outdoor band clutter.
Home run and touchdown!"
Woah hold on there before starting that play. Let's take a closer look at this situation.
You are correct, the CC signal will be delivered directly to homes and businesses via the power lines and right up to their wiring in the home or building. And yes the CC signal will be like as if their radios are in the same room as your TX is.
However, you have to remember that their radios still have that internal ferrite bar antenna and still picks up over the air signals at the same time your signal is present on the AC wiring. It is that very reason why you have to be very careful in choosing a frequency. There could be someone who may listen to a station on one of those frequencies and has set up an elaborate antenna or even a simple long wire to pull those stations out from the clutter.
This could be a problem for both that person and your CC operations. Remember what I was pointing out about choosing a frequency in CC. That preventing interference is even more crucial than that of a simple wire antenna setup or 3 meter antenna setup. Because your signal has a better chance of penetrating into homes than would the short wire or 3 meter antenna, you could cause interference even more with a CC system.
Also keep in mind about the potential for inductive interference to telco and cable systems. There are frequencies in the MW band that may cause the inductive interference more than other frequencies. For example, the frequency 570 might not cause much interference at all to other services, but 970 might. Or it could be the other way around, 970 causes inductive interference while 570 does not.
As I pointed out also..CC is a "flux science". And you can sit with calculations all day long and apply something from those figures to the real world and discover a whole different result. CC is a bit tricky..sometimes stubborn.
But don't be discouraged by all of that. It is all a part of learning what will work and what won't work. And is why I suggested the PLL route instead of crystals to begin the testing. After a couple of crystal purchases the expense begins to add up..and that of course will give reason to become discouraged.
Just keep these things in mind when doing your open frequency testing. Never leave any stone unturned.
RFB
Got it couch!
That's why I'm declaring this National PLL Week. This week everyone on the team will become proficient with PLL applied to radio transmission.
No broadcaster will be left behind.
Class......Class..........Class............SHADDDDUUUPPP!!!
Thank you.
(from a Cheech and Chong "Class Teacher" comedy skit)
Ok instead of building a variable oscillator from scratch and because my parts bin is somewhat empty, why not take a known working design and modify it slightly to be PLL controlled!
The following modified oscillator is based on Wenzel's "phono2" variable oscillator...found HERE. The original design is 2/3 way down the page.
I have built this "phono2" circuit a couple of years ago prior to replacing the exciter board in my LPB TX 2-20 unit with the C.Cuff C-QUAM board. It was during my testing to find a suitable frequency and since I did not want to spend money on crystals, this was the way to go and it works great.
And HERE is the modified design schematic with component values..including part number for the varactor diode.
Use a 9 volt regulator tapping the 15VDC rail in the TX for this oscillator's power supply.
The inductor coil is a salvaged local oscillator coil from a non-working AM radio. The coil winding to use is the hi-side, or higher resistance side. Leave the other pins unconnected. For added stability, ground the metal case of the inductor to circuit ground.
Tune the inductor so that the oscillator is operating close to the desired locking frequency. Then enter the frequency code into the PLL and the oscillator will lock.
In Wenzel's design and intent, his circuit was designed to accept audio modulation at the base. Since we do not need the oscillator modulated, the adjustment for audio and input for audio part of the circuit has been removed.
Once the desired operating frequency is entered into the PLL keypad, the oscillator may jitter before locking. Simply tune the inductor very slowly until the oscillator locks and the jitter stops.
The output of this circuit feeds pin 8 of A3's socket, or the frequency test point slug on the exciter. The oscillator puts out a relatively low signal level but adequate enough to drive the balanced modulator and exciter amplifier to produce enough final power of about 8 watts, plenty for the purposes of frequency hunting.
Now..get busy! :p
RFB
Thank you RFB for this tutorial, the idea behind the PLL is coming clearer the more I avoid doing anything about it.
So, I have printed your instructions and the circuit, and am getting to work.
Here are some early questions.......
I do not have a non-working AM radio to scavenge a local oscillator coil, but I think that's a catalog item....
There are two items described as 1uH, but they are drawn with different symbols, so could you please give a description of how they differ?
"The oscillator puts out a relatively low signal level..." Can that be improved by not using resistor 2.2k ?
Will PN2222A work in place of 2N4401 ?
RELATED QUESTIONS
This is a carrier current thread, but we are also considering the PLL over on the long wave project, so here are two questions about that:
Will this same oscillator work for long wave?
Will the PLL keyboard somehow allow using 162kHz?
Re-load the image for the modified schematic..I left out one component between the varactor and inductor. Everything else is the same.
Answers in order of questions in post:
"I do not have a non-working AM radio to scavenge a local oscillator coil, but I think that's a catalog item"
Yes. These can be ordered at Jameco or Digi-Key. Simply search for "AM Local Oscillator coil". See HERE.
"There are two items described as 1uH, but they are drawn with different symbols, so could you please give a description of how they differ?"
The reason for their difference in the drawing is because there was no room to draw a curly coil in the space where the square is drawn. The value is the same..1uH, what is referred to as a "molded choke".
"The oscillator puts out a relatively low signal level... Can that be improved by not using resistor 2.2k?"
The 2.2k resistor provides some padding between the oscillator output and load. Removing it would also remove that padding and isolation from the oscillator, and more than likely will prevent it from oscillating correctly. Leave the 2.2k resistor in circuit!! If you want to increase the oscillator output level, add a simple buffer amplifier stage. I will draw up one shortly and post as an addition within this post later.
"Will PN2222A work in place of 2N4401?"
You can look up the specifications for each transistor and note their maximum and minimum voltage ratings and operational ranges as far as gain and frequency. Since that Wenzel oscillator was designed around the 4401 and the working voltage of 9VDC and inductor values (not the variable), swapping out with a 2222A may have some issues such as unstable oscillation and/or multiple oscillations across the transistors frequency curve. In other words, the oscillator may not oscillate at a single frequency, but dozens and appear like the teeth of a saw on the spectrum analyzer. It's best to use what the circuit design calls for..the 4401. But feel free to try a 2222A. At 9VDC with uA for current draw, nothing will blow up in your face. 😀 The worst that could happen is the oscillator simply doesn't oscillate or as described...oscillates unstable.
"Will this same oscillator work for long wave?"
Not with the part values listed, which is for the MW band. But the basic design of the circuit can be used for LW frequencies. Things like the LC tank, the feedback loop and coupling component values will have to change for the lower frequencies. The same transistor can be used.
"Will the PLL keyboard somehow allow using 162kHz?"
Yes. Punch in 000016, and after the LED flashes indicating it took the entery, use the up key to step up to 162. The manual says 10khz steps, but it is really 1khz steps.
Buffer stage:
HERE is a schematic for a simple one transistor buffer stage with parts list. Sourced from HERE.
RFB
Thank you for the clarifications.
In the last post RFB wrote:
"Re-load the image for the modified schematic..I left out one component between the varactor and inductor. Everything else is the same."
I re-loaded the image for the modified schematic and it was identical to the previous image I had printed. I think perhaps the first time I downloaded the image it had already been up-dated. Just to make sure, tell me which part had been excluded from the first image posting.
The correct schematic will have a 10pf capacitor between the varactor diode's cathode and the variable inductor coil, right after the 1uH "square" choke.
RFB
I am now certifiable and have completed this phase of the PLL education.
I have no more questions at this time, a very rare event, possibly mistaken.
Probably there is a question I should have, but what would it be?
"Probably there is a question I should have, but what would it be?"
Without questions, there can be no answers. Without answers, there can be no progress.
The first step to wisdom is "I do not know".
The first step to knowledge is asking. 🙂
RFB
My friend in New Jersey has been able
to look at it on the bench. He has
taken some measurements and will probably
have some recommendations. So now it's
in the pipe, so to speak.
He says he will have it in the mail after
he does the evaluation.
So, this is starting to move.
We'll see what happens.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
That is good news, DOG 2, when you get the unit working will you be trying carrier current?
First of all, the transmitter
cannot be on 860 kHz. (This is
where it is now.) So that will
have to be changed. I will at
least have to get 3 new 6AL11 tubes.
That is what the unit needs.
I had made a coupler before for my
Panaxis transmitter. (I no longer have the
Panaxis.) It WAS actually a big loop receiving
antenna for the AM BCB. I cut into the loop
so that it became a big LC on the output of
the Panaxis. Then I wound the AC cord
around the loop, which was feeding the
Panaxis. After that I plugged the AC cord
into the wall, got the carrier on the radio,
and tuned the loop for max signal.
So, I plan to do the same with the RC-6A,
except the 6 watt signal will be attenuated
to a watt or two. That way the transmitter
will see a load from the attenuator that
is not too far off the mark. Then I will
take the RF energy from the output of the
attenuator and feed it to the homemade
coupler. Whether or not it will really work
remains to be seen. But I want to try it before
I try anything else because it is easy.
By the way, I plan to ground the transmitter itself
to a water pipe, but my plan is to not ground the
AC cord. It will be connected at hot and neutral,
but not at ground.
That's the only idea I have now. It may be possible to
get a real coupler from my engineering friend here
in Connecticut, but I want to try this idea first.
Beggars can't be choosers. I know now that the RC-6A
is in the pipeline. So now, we'll just wait.
Best Wishes,
Bruce DOGGRADIO STUDIO 2
We already know you will report the results of your plan, and it will be interesting to learn from it.
If RFB is tuned in, maybe we can get an estimate of what might happen with your approach, Dog 2.