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40m Portable E Transmitter




 
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Author Topic: 40m Portable E Transmitter  (Read 2692 times)
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ka1tdq
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« on: April 10, 2022, 11:23:00 AM »

Time for another E-build! I bought a new Icom 705 portable QRP transceiver and built a portable antenna to go along with it. I've been using it around San Diego on the waterfront and parks with great success. We're selling our house and downsizing so portable operation seems to be the way to go. It got me thinking about how to use an E transmitter on the go.

PWM is a definite must as power efficiency and weight are key. Also, my portable antenna telescopes to 17 feet and won't tune 75 very well, so the transmitter would need to be designed for 40 meters. The antenna loads 40 very well.

The plan is to have everything self contained between the two boxes of the the Icom-705 and the E-rig. Power for the E-rig will have two 12 volt at 9 amp batteries driving two 48 volt inverters in series (96 volts total). Drive for the dual phase IXDD drivers will come from the Icom via a toroidal transformer. Varying the drive, minimal will be required, will vary the amplitude of the sine waves and thus the duty cycle. The Icom will also function as the receiver.

A 3-position, multipole make-before-break rotary wafer switch will act as the mechanical sequencer.

I'll have a rudimentary overcurrent limit protector on it to cut off drain voltage if drain current gets too high. Nothing fancy, just cycle power to reset it.

I have two SicFets since they have lower gate capacitance, a critical factor on 40 meters.

Target power is 50 watts carrier. A potentiometer will vary the resting carrier voltage via the PWM. I'll see what voltage is required to get me to 50 watts with clean drain waveforms.

I just welded the chassis this morning. After I paint it red later I'll post pictures. It has a carrying handle necessary to lug the thing around.

Of course, using an E rig on the road with changing antenna conditions will require a peak at the waveforms to make sure everything is fine. I bought a handheld, 2-channel oscilloscope for on the go as well.

I'm excited!

Jon

** By the way, I submitted the antenna build to QST as an potential magazine article. Here's the link to what I submitted:

http://ka1tdq.radio/portable-multiband-hf-antenna/


* 40m SicFet E transmitter.jpg (3405.7 KB, 4032x3024 - viewed 204 times.)

* Portable multiband antenna.jpg (1933.36 KB, 2016x1512 - viewed 186 times.)
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KD6VXI
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« Reply #1 on: April 10, 2022, 06:35:07 PM »

I appreciate the tenacity of your builds, but I have to wonder.....  Would not a single mrf300 accomplish the same thing with less complexity?

One 48 volt inverter would power it to 300 watts pep. Overall system efficiency should prove to be about the same, what with a PWM, pair of inverters, etc.

In addition, the mrf300 would give you linear operation on ssb and cw.

I'm looking at doing something similar with a Raspberry pi, hermes lite and a class E rf deck using EER to have amplification.  I want to take it to the end of our 1200 foot pier out over the Carribean.

So many projects, so much other stuff to do.

--Shane
WP2ASS / ex KD6VXI
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ka1tdq
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« Reply #2 on: April 10, 2022, 08:42:42 PM »

I'm not sure I follow. The Carribean sounds good though! Wink

Here's the look of the unit. RF deck on top and PWM, meters, batteries, overload trip, inverters and controls on bottom.

I'm flying out to Vegas in a few weeks for a weekend trip. Let's see if I can catch the watchful eye of the good casino folks again with this stuff.

Jon


* IMG_2903.jpg (1301.48 KB, 2016x1512 - viewed 183 times.)

* IMG_2902.jpg (643.02 KB, 2016x1512 - viewed 172 times.)
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ka1tdq
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« Reply #3 on: May 08, 2022, 09:27:47 AM »

I've made lots of progress, too much to type. I do have a webpage address for it though. Check it out here:

http://ka1tdq.radio/portable-40m-class-e/

Jon


* Class E testing-2.jpg (1259.54 KB, 2016x1512 - viewed 143 times.)
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M0VRF
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« Reply #4 on: May 08, 2022, 12:00:26 PM »

Funny....The American version of 'Portable'!

Here's something you could slip into a jacket pocket.

60W carrier.

JB.


* PXL_20220418_195820772.jpg (1762.07 KB, 3840x2160 - viewed 180 times.)
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ka1tdq
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« Reply #5 on: May 08, 2022, 12:24:43 PM »

That is one difference Iíve seen between American and European builders. We overkill here. This is 38 lbs. As much as I try, I can never seem to master miniaturization.

Jon
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vk3alk
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« Reply #6 on: May 08, 2022, 07:21:34 PM »

Hi Jon...

Had a read of your Blog and all looks fine to me...
Gate waveforms Ok and all that kind of stuff....

Size doesn't matter as its your style  Smiley


Wayne
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W7TFO
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« Reply #7 on: May 08, 2022, 07:40:51 PM »

Is everything truly bigger in AMerica, or is it just littler in Europe?

73DG
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ka1tdq
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« Reply #8 on: May 09, 2022, 01:12:23 AM »

Funny story. I took this project to Balboa Park in San Diego to do a little building outside. Apparently that's not done too often here. I garnered lots of attention. Gladly they left me alone but I'm not going to attempt that one again. People don't build anymore, or even know what it looks like, so... yeah.

Jon
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M0VRF
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« Reply #9 on: May 09, 2022, 01:57:17 PM »

Nice one Jon, you're doing a fine job!

Miniturization is something I've always loved and SMT really helps, that and a PCB of course.

I have to sell commercially so it has to be done this way as it's cheap and fast!

Do like you builds btw, guess I'm a bit jealous!

JB.
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ka1tdq
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« Reply #10 on: May 22, 2022, 01:48:03 AM »

I built a drain overcurrent and RF overdrive protection circuit board and made more progress. Here's the video link showing the latest:

https://youtu.be/ppTtr15PYMk

Jon


* Overcurrent and Overdrive.jpg (2545.05 KB, 4031x3023 - viewed 136 times.)
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