transmission prevention

[laplace]

Hi, new to the forum.

I recently got what I needed to build a audio amp with some Eimac outputs, and came up with a circuit for class D amplification.


Could I get some real numbers regarding how much RF ''leakage'' a HF transmitter has during operation?

Thanks in advance.

 

[dkcorlfla]

Hi, new to the forum.

I recently got what I needed to build a audio amp with some Eimac outputs, and came up with a circuit for class D amplification.


Could I get some real numbers regarding how much RF ''leakage'' a HF transmitter has during operation?

Thanks in advance.

Welcome to the forum. There are a lot of helpful people here but your question is very vague. Don't think anyone can come up with a generic number on RF because it is going to vary greatly from station to station depending on how it is setup, what equipment, how well it's grounded, what antenna and how well it is tuned, power output and so on.

Perhaps if you could provide more detail on what you are trying to build and how it will be use somebody could provide some info on what the amp is going to need to shield it.

 

[laplace]

Thanks for replying.

Sorry about the vagueness.

So a 12AX7 drive 6L6 drive 4cx150 in PP ''class D''
Theoretic continuous power is probably over 2000W.

The output stage converts the bits back into a continuous signal, so main worry is the 6L6, which is feeding 15 watts of 1MHz to 35MHz to to the output.

The chassis housing the 4CX150 is a decommisioned Navy trasmitter, I bought on auction. T217AGR.
I beleive the unit was air to ground comms.
Beefy steel plates.

I dont have much experience in moving significant power at these frequencies.
None actually. The most Ive done at MHz and above is about 250mA of 5v.

 

[AK9R]

Are you talking about building an audio amp that will modulate an RF transmitter? If it's an RF transmitter, what radio service will it operate in?

 

[laplace]

Are you talking about building an audio amp that will modulate an RF transmitter? If it's an RF transmitter, what radio service will it operate in?

These modulate at MHz.

But it drives an inductive load in the final stage, which smooths the pulses.

So I think the 4CX are ok.

Still have 15W of the 6L6 that is unshielded sockets, transformers that are not in this chassis.

I have taken the liberty to assume the transmitter was designed to not leak even with the 4CXs being pushed hard.

 

[AK9R]

Wearing my moderator's hat, I'm trying to figure out where this thread belongs. It is currently in the HF/MW/LW Equipment forum of the HF/MW/LW Monitoring group. I think we are talking about a transmitter and not a monitoring device. Hence, the thread may be in the wrong place.

What radio service is this transmitter intended for?

 

[dkcorlfla]

--snip--
What radio service is this transmitter intended for?

Now that's the question that needs an answer! Now I'm getting curious.

 

[kb3ouk]

Sounds like you're building a plasma speaker? Basically a modulated RF Tesla coil?

 

[dkcorlfla]

Sounds like you're building a plasma speaker? Basically a modulated RF Tesla coil?

That or maybe a kick ass arc welder ;-)

 

[EAFrizzle]

12AX7s driving 6L6s, 6V6s, or 5881s sounds like it needs a Strat plugged into it.

 

[laplace]

Wearing my moderator's hat, I'm trying to figure out where this thread belongs. It is currently in the HF/MW/LW Equipment forum of the HF/MW/LW Monitoring group. I think we are talking about a transmitter and not a monitoring device. Hence, the thread may be in the wrong place.

What radio service is this transmitter intended for?

Hi sorry about the slow reply, Ive had a lot on my hands.

The idea is to modulate the incoming signal, and turn it into binary pulses very much like radio, except no continuous wave.

And the output would be driving a loudspeaker directly, so any energy leaving the amplifier is an unwanted product caused by the high speed switching.

For the sake of simplicity Ive avoided drawing the entire circuit, but hoping the basic idea is graspable?

if not i will attach all of it.

I am looking at the powersplitters for this, which are telling me even at low power I need 1/4in aluminum shielding.
Is that kind of how it goes? The last thing I want is for this thing to leak MHz square waves in all directions.

Thank you all for answering.

Best

Sounds like you're building a plasma speaker? Basically a modulated RF Tesla coil?

If I were immune to ozone, this would be a great idea!
But they will be driving 8 ohm speakers. Ive got a bit of a clock generator mess going on.

I am trying to avoid DSP and memory based digital noise control.
I get promising results with powersplitters, and frequency mixing multiples.

As a side note, I have found this to be much more elegant than LC tanks at filtering frequencies.

 

[kb3ouk]

Ok so now it all makes sense. Basically its just a regular class D switching audio amp but the switching frequency is several MHz instead of about 100 kHz. Since that's passing through a output transformer and a resistive load (the speaker) I don't think you'll have anything to worry about leakage.

 

[laplace]

Ok so now it all makes sense. Basically its just a regular class D switching audio amp but the switching frequency is several MHz instead of about 100 kHz. Since that's passing through a output transformer and a resistive load (the speaker) I don't think you'll have anything to worry about leakage.

Thanks for your reply.

This would be considered a Class D mode of operation. Or a hybrid mode.

This particular pulse modulator is quirky, I havent seen it pursued by anyone...But you are spot on. The output being switched at MHz and some of it ending up in atmosphere is my main concern.

I will try applying some signals in the 6L6 without being too worried.
Best.