new tx idea

Robert has listed some good design points to ponder which I will do at a leisurely pace. Always looking for good ideas so thanks.

Neil

Radio At a Leisurely Pace will be back in 4-weeks.

Meanwhile, this interlude from MICRO1700's Dog Leash Music Service.

I may have more slow announcements later, or better still, tomorrow.

The temperature is being shown on the thermometer, and I may summon up the interest in heading over there to get a reading, that will be day after tomorrow.

But now, let's think about getting that music started. Just a minute. Make that just an hour.

And now for some "Dog Leash Music,"
in 13/4 time.

Bruce, "W 60 H Z" 1020 AM CC

P.S. Those are really good ideas.

I sure left myself open for this one didn't I?

I think I will take my time working on a comeback.

Neil

The "balanced modulated final" is of the dual rail supply variant and modulated with a true balanced modulator..ie feeding BOTH the + and - supply rails.

I came up with that concept..only to be talked down by another transmitter maker.

Don't see him poking around in here naysaying..do we?!!

Let credit go to where credit is due.

He will now I bet.

Pick and choose....seems to be the game lately..everywhere.

Which is lesser of the two evils....to even consider that an option is in of itself incredibly stupid.

RFB

shielding the toroid minimizes the detuning effect of your hand near it to change jumpers, according to mark the dual rail balanced modulator final setup will modulate to 150% plus in the positive. the large trimmer cap is part of the ATU/toroid. appreciatively isolated stages prevent influence of each stage on another and prevents stages from dragging down the oscillator. the dds/crystal oven is self explanatory, the stages and how they lay out and the class e are also self explanatory. the balanced 600 ohm is self explanatory.

On the one hand I can realize that shielding a torroid by, in essence, putting it in a mini-Faraday Cage, would prevent physical hand proximity from de-tuning the toroid, but (on the other hand) I would think the shield would of itself cause the toroid tuning to change by some amount, thus requiring a different toroid winding to stay on tune while also being shielded.

Carl raises a good point about shielding. Wouldn't this also produce a capacitive coupled path to circuit ground which could shunt some of the signal away from the output thus reducing the power to the antenna?

From RFB's post it appears some of this has been discussed before. Is there more we should know?

Neil

Knew a guy named "Lee Gerdine". He was prominent and sometimes controversial, so I nick named him Leisure Dean.

But seriously, I have invented a life style that might actually bring new ideas for radio formats; "slow paced" formats.

I'm cleaning a rain gutter above the front steps. It's tricky, and involves setting the ladder partly on stacks of bricks to place it right on the steps.

Rather than rushing and trying to finish in 10-minutes, I've made it an all day project. I started by removing fallen leaves from the steps by hand, one at a time, then piled bricks with great care so the stack did not wobble. There is a rain storm predicted in 1-hour 20-minutes, so I might just skim by.

The radio is tuned to one of my radio stations, who knows where it's transmitting from, even I don't know.

I sometimes look at all the other work that needs to be done, and I say, "I'm busy right now."

Take time off to post this great idea, think about lunch, possibly finish the gutter in 2013.

It's slow, it's easy. The eventual station.

Since we are discussing both the technical details of Robert's list and the methodology used to accomplish tasks (prompted by my leisure comment) I will add to what Carl just posted.

Many times when planning a task which I have not done before or don't know how to proceed I use a process which I call "sit and stare". To the casual observer (my wife usually) it appears that I am goofing off but the mind is at work and body motion is in pause mode.

What I enjoy as much as completing a successful project is my wife's remarks about how well it turned out or how easy it appeared. I tell her about "sit and stare" being a planning process and she is becoming a believer.

So, as we develop and discuss Robert's suggestions and exchange ideas about these I will be sitting and staring, leisurely by the way.

Neil

Based upon Neil's analogy, I must be one of the great planners of all time.

Now, if I could just get out of the pause mode.

I am prepared to look at Robert's plan and make comments:

Here is a re-print of Robert's transmitter idea:

"shielded low loss toroid matching coil

large trimmer capacitor

crystal oven locked dds synthesizer

oscillator followed by buffer followed by balanced modulator than class e balanced final

capacitive isolated stages

balanced 600 ohm 0dbu audio input"

I have already made my comment about the shielded toroid coil.

Let's talk about the large trimmer capacitor. Why is it large? Why not a small trimmer capacitor? Should the trimmer be shielded to some degree?

As to the crystal oven, I understand that using a crystal oven with a crystal oscillator helps maintain frequency stability, but I do not know how stable a DDS synthesizer is and whether it also would benefit from a crystal oven.

"The capacitive isolated stages" stumps me. I do know that RF stages can be coupled by capacitors or tuned-circuit transformers, but I don't understand why either one could be called "isolated".

A balanced 600-ohm input at 0dB would be standard of a professional device, and some of the part 15 transmitters already have that feature, and of course it can be easily added to a consumer transmitter, so it's not unusual. Further, I believe the complete transmitter should have the option of -10dB unbalanced input, for the most typical user.

I've saved the best for last

"oscillator followed by buffer followed by balanced modulator than class e balanced final"

The only difference between this and at least one other part 15 transmitter on the market is the balanced modulator. I noticed that RFB has mentioned writing about this in the past, but I don't remember. Can we have the explanation again about why a balanced modulator is better?

Typically, balanced modulators are used in single-sideband (SSB) AM transmitters to suppress the carrier frequency. This creates double sideband, suppressed-carrier AM, which then is spectrum-filtered by some means to produce the sideband that is desired to be transmitted (either the upper or the lower r-f sideband).

To receive such an r-f waveform without severe distortion requires the receiver to re-insert the missing carrier before demodulation of that SSB signal.

The program audio applied to an SSB transmitter could be processed to produce greater modulation percentage in the positive-going AF polarity than the negative-going AF polarity, but that is equally possible for transmitters not using balanced modulators.

Thank you rich for clarifying the purpose of balanced modulation.

I was way off the beam, because I thought Robert was talking about a medium wave AM transmitter.

SSB (single-side-band) is, I am sure, a shortwave technology.

I'll stand aside for awhile until I have a better idea what's going on.