"Indestructable" Transmitter??

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"Indestructable" Transmitter??

Postby steve_qix » Fri Mar 03, 2006 5:51 pm

Hi!

Well, I've been using the new class E-Z transmitter for about a month now... and have run an extensive
battery of tests designed to prove the robustness of the design under adverse conditions.

To quickly recap the design: The transmitter is a 10 MOSFET transmitter designed to run about 300 - 400 watts of power.
The RF amp uses a single driver IC for each module, and the rig is bandswitched between 80 and 160 meters. The
modulator is a small Pulse Width design.

The tests:

1) At full power, and under modulation, repeatedly short-circuit the RF output, both at the
transmitter and along the feedline. Rig shut down each time; no failures.

2) At full power and under modulation repeatedly disconnect the antenna at several
points. Rig shut down each time; no failures.

3) Attempt to operate the transmitter at too high current. Rig shut down each time; no failures.

4) At full power and under modulation remove the RF drive. Rig shut down each time; no failures

These tests were repeated on purpose, and by accident numerous times.

I am in the process of creating complete schematics of the entire transmitter, modulator
and power supply. Also laying out a PC board for the modulator and associated
control and protection circuitry. The design is complete from microphone to
modulated output. The layout will accept up to 6 MOSFETs in the modulator
output section (up to 1200 watts of modulated DC) and includes all drivers, pwm generator,
8 pole Butterworth input filter, negative peak limiter, tone compensation (mic preamp), etc.

The builder can opt to not populate whatever sections of the
PC board are not needed (such as the mic preamp, if this is not desired, or the
output section, etc. etc.).

The board layout is flexible enough to allow it to be used in a wide variety
of applications and transmitter designs.

I am absoultely looking for feedback, if anyone has any. 8)

Regards,

Steve
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input

Postby RidgeRunner » Tue Mar 14, 2006 4:24 pm

Well I dont have anything techical to offer other than I would be interested. One thing that I would think that would be helpful to newbies like me is some soft of definition of terms...like modulator. Also possbile a recomended setup for a first time class e builder. What I find confusing...which I am figuring out as I read more and more. is what exactly am I going to need for equipment to puke out some AM on 75 and 160. From what I gather need some sort of exciter that will give some RF input and freq control. Then there is the class e amp it self, the power supply and the modulator....is this where your audio input goes? Or are you feeding your audio thru your rice box. I have been itching to build one of these since my rice box alone leaves me feeling disappointed on the air. Another thing I wouldnt mind seeing is for a guy like me with hardly any junk parts if I was to go out and buy all new parts what am I looking at for taking a hit in the wallet, I know that I could just figure it out by going to mouser or something, but I am curious what somebody else is coming up with too.
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Re: input

Postby steve_qix » Fri Mar 17, 2006 10:12 am

RidgeRunner wrote:Well I dont have anything techical to offer other than I would be interested. One thing that I would think that would be helpful to newbies like me is some soft of definition of terms...like modulator. Also possbile a recomended setup for a first time class e builder. What I find confusing...which I am figuring out as I read more and more. is what exactly am I going to need for equipment to puke out some AM on 75 and 160. From what I gather need some sort of exciter that will give some RF input and freq control. Then there is the class e amp it self, the power supply and the modulator....is this where your audio input goes? Or are you feeding your audio thru your rice box. I have been itching to build one of these since my rice box alone leaves me feeling disappointed on the air. Another thing I wouldnt mind seeing is for a guy like me with hardly any junk parts if I was to go out and buy all new parts what am I looking at for taking a hit in the wallet, I know that I could just figure it out by going to mouser or something, but I am curious what somebody else is coming up with too.


Hi!

This information may or may not be helpful. I've been updating the class E web site over the past couple of days, and in addition to other areas, I've expanded the section on AM Transmitters to include general information about building a station. Check out http://www.classeradio.com/review.htm and see if it's helpful to you.

Let us know what might be helpful so this can be added to the site. If you have questions, chances are others have the same questions!

Thanks and Regards,

Steve


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Postby frank carcia » Fri Mar 17, 2006 11:59 am

Steve,
I wonder if you ever considered AC coupling the driver chips to the final gates as a way to isolate them. A nice low Z chip cap with a 10k resistor across gate source. this would eliminate th ecascading failure mode.
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Postby steve_qix » Fri Mar 17, 2006 12:30 pm

frank carcia wrote:Steve,
I wonder if you ever considered AC coupling the driver chips to the final gates as a way to isolate them. A nice low Z chip cap with a 10k resistor across gate source. this would eliminate th ecascading failure mode.


Hi Frank,

That idea has DEFINITELY crossed my mind, and I think it's a good one.

Currently, I'm experimenting with using 5 of the IXDD414 driver ICs (less than $3.00 each) driving 5 MOSFETs and NOT connecting them in parallel. I've made a number of measurements on the prop delay differences, and the devices are virtually identical. This is all on 40 meters.

Bill, KE1GF is doing something similar, only with 2 driver chips instead of 5. The experiments are continuing, but this may prove to be workable...

Regards,

Steve
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Postby frank carcia » Fri Mar 17, 2006 12:39 pm

hi,
A nice .37 or .47 UF chip cap with a nice wide PC trace to the gate would be a nice low Z. Cool on 5 in parallel I hope they are all the same temperature... I played with AC coupled drivers back in the 80s. and stacked 3 chips .1 uf I think. it worked OK as long as a resistor is across the gate source. Today the drivers are a lot stronger.
Remember me if you buy a bunch or driver chips. I will jump in if you can get a price break. I think the 75 meter rig is next now that the 160 rig is back on. Conditions were so poor this winter I wasn't motivated.

SDR project about done, shipped a board to the guy who did the art work.
It works cool. Getting ready to go back into construction mode in a couple weeks.
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Postby n1ps » Sat Mar 18, 2006 1:42 pm

Hi Steve,

The schematic looks great. I do have a couple questions (dumb or otherwise)...questions I failed to ask you the other day in person...

1. How do you perform PTT in this RF amp?

2. On the RF input, do you use an A/D converter to attain the TTL level or did you just set it via a scope?

3. Are you driving the input with a rice box?


I think it is time we come up with a DDS VFO. The QRP crowd has been working this pretty good. There is a "kit" for $200 which is a little pricy to me. I think we could come up with one for under $100. I'm not conversant in PIC programming, but I know people who are.

TNX

:D

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Postby steve_qix » Wed Mar 22, 2006 6:55 am

Hi Pete,

Let me see if I can answer your questions. Other folks are probably asking the same thing :-)

The PTT (transmit/receive) for this transmitter is keyed by my main station's transmit/receive system. The sequence is like this:

1) Upon throwing the transmit/receive switch, the antenna is disconnected from the receiver antenna bus, and the receiver inputs are shorted out. The antenna is connected to the transmitter output. The VFO is activated. 120vac keying voltage is sent to all transmitters.

2) The 120vac keying voltage activates a relay in the transmitter. Upon the presence of RF input (5v), the transmitter activates a relay, sending power to the RF driver power supply, sending power to the driver ICs.

3) When the RF driver power supply is up to voltage, the relay for the main power supply is activated, sending both AC voltage to this power supply, and connecting the DC output of this supply to the transmitter high voltage circuits.

The relays are all interlocked, making it impossible for high voltage to be applied to the transmitter unless the RF drive is operational.

When going to receive, a sequence is also followed:

1) The high voltage is immediately removed from the system. The driver IC power supply is turned off.

2) After a very short delay, the antenna is switched from the transmitter to the receiver and the VFO is deactivated.

--

The RF input is a 5v sine wave fed to a schmitt (sp?) trigger, with a DC offset. The DC offset comes from an op-amp, connected to a rectifier that converts the output of the schmitt trigger to a DC level. A pot sets the dc level going into the other input of the op-amp, allowing you to adjust the on-time / off-time symmetry. Since this is a negative feedback circuit, symmetry is maintained over a wide range of input voltage levels.

--

The RF is, at this time, obtained from a rice box working into a 50 ohm resistor followed by a divider, to get the 5v p-p needed for the schmitt trigger. Anything that will produce around 5v of RF will work.

Hope this helps!!!

Thanks and Regards,

Steve
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