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40 meter 8 FET transmitter




 
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KD6VXI
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« Reply #25 on: August 12, 2016, 11:25:19 PM »

 As it turns out, the easy part was building the RF deck.  There's MUCH more work getting everything else done that's needed for the transmitter, but I'm getting there.

Jon

YUUUP!


--Shane
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ka1tdq
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« Reply #26 on: August 13, 2016, 07:50:03 PM »

Like Tom Petty says, the waiting is the hardest part.

Here's a 10 hour loop of Mission Impossible to kill some time...  Smiley

https://www.youtube.com/watch?v=FCO95esUzBw

...or more fun, 10 hours of Benny Hill

https://www.youtube.com/watch?v=8yoSM9G00b0

...and if you've watched that video, you REALLY need to watch this one!

https://www.youtube.com/watch?v=SKb_zHHNvY4

Jon
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ka1tdq
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« Reply #27 on: August 19, 2016, 09:43:36 AM »

The power supplies are all built.  The top is the 3 volt negative peak limiter supply, then 11 volts for the IXDD bus, and then 48 volts for the drains.  The drain voltage will get dropped a little bit by the Heising choke.  

Jon


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ka1tdq
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« Reply #28 on: August 27, 2016, 12:44:23 PM »

The audio amp arrived.  It'll be on its own 120 volt circuit and the power supplies for the RF deck are on their own as well. 

I'm waiting on the Heising choke and I'm still building the sequencer.  Haven't gotten to the antenna yet.

Jon


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ka1tdq
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« Reply #29 on: September 10, 2016, 07:28:56 AM »

The choke just arrived.  Now I just need to finish wiring the Heising circuit along with the negative peak limiter.  The series diode for the negative peak limiter will be mounted on the PVC cap in the picture. 

The two gold resistors are 50 ohms / 100 watts each.  In parallel they'll be 25 ohms and be connected between the "open" end of the Heising capacitor and ground.  The audio amp output will be switched into the circuit in a properly timed manner. 

I was actually disappointed when the choke showed up... I was hoping for something bigger.  Now this rig won't qualify for the Heavy Metal category.

Jon


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ka1tdq
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« Reply #30 on: September 16, 2016, 04:26:16 PM »

Done.  I just finished the modulator and it appears to work very well.  I've set the carrier for 400 watts and I'm getting 1500 watts PEP when I do a "Helllloooo radio" in the microphone.  Everything sounds good in the headphones when listening to the direct RF pickup on the back of the transmitter.  I still need to tweak things a little bit, but the first test was good.  No smoke and it didn't blow up.  It doesn't take too long though before my MFJ cantenna gets hot.  More testing needs to be done with a real antenna.

And that's my next thing to do... I need to put up a 75 meter dipole.  I have all the stuff, I just now need to build it. 

So, barring any surprises, after I get the dipole up I'll be on 75 meters class E with a half decent carrier.

Jon


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WD5JKO
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« Reply #31 on: September 18, 2016, 02:56:31 PM »


Jon,

  I have been watching your progress. I presume to make room for this rig that the dual 3-500z linear went bye bye?

I am sure I will copy you from Central Texas once the noise level drops.

Keep up the good work Jon. You inspire a lot of folks to get off their butts to build something.

I thank you for that.

Jim
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ka1tdq
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« Reply #32 on: September 18, 2016, 03:16:42 PM »

Thanks Jim.

Yeah, both the dual 3-500 and the triple 3-500 amplifiers are gone. I'm just a solid state guy now. Not that there's anything wrong with tubes, it's just that I didn't want the danger of high voltage around with little kids.

I also pride myself now on not having typical amateur commercial gear around. Other than a few MFJ trinkets and an SDRplay, I'm all homebrew. I need the SDRplay though... I probably couldn't build a receiver if my life depended on it.

Anyway, the antenna will be up in about two weeks when I can get my hands on a tall extension ladder. It's going to be a fan dipole for 75, 40 and 20 meters.

Jon
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w8khk
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« Reply #33 on: September 18, 2016, 03:27:30 PM »


Keep up the good work Jon. You inspire a lot of folks to get off their butts to build something.

// snip //


You are right Jim....  Jon, keep up the good work, you have inspired me too.  I will be watching how you make out on your 40 meter rig.  I will probably follow your lead after I get the rig finished for the other two bands.  I understand 40 is a bit more of a challenge than 75 or 160.

I got off my butt and finally put together the WA1QIX three-board set: the PDM generator, PDM output, and the Overload/Efficiency boards over the past couple weeks. (I have had the parts in the zip-lock bags for over a year.) Am now waiting for shipment of the VFO and two-phase driver board.  

Currently doing the metal work for the power supply and modulator in one cabinet, and the RF section for 160 and 75 in another.  I am using a couple HP instrument cases, suitable for either desktop or rack installation.  

All the other parts are here, even the power transformer and filter capacitors.  I have a transformer that provides 88 volts RMS at 15 amps from an HP tape drive, and four computer grade electrolytics, 77,000 uF at 175 volts each.  I think two should be sufficient for one rig.  I will go with the tried and true 400 watt RF unit, using two modules of 4 FQA1190 FETs in each module.  I am building out the modulator to go a full gallon down the road.

I am recycling as much as I can from the old computers, for instance some massive heat sinks.  But for all the other caps, resistors, and solid state components, all new purchases.  I will post some photos once I finish the metalwork and start assembly.
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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #34 on: September 18, 2016, 11:57:01 PM »

...and of course, the associated YouTube video.  If you have 4 minutes to kill, here you go:

https://youtu.be/74LZiuD1qqQ

Jon
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steve_qix
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« Reply #35 on: September 19, 2016, 09:41:05 AM »



All the other parts are here, even the power transformer and filter capacitors.  I have a transformer that provides 88 volts RMS at 15 amps from an HP tape drive, and four computer grade electrolytics, 77,000 uF at 175 volts each.  I think two should be sufficient for one rig.  I will go with the tried and true 400 watt RF unit, using two modules of 4 FQA1190 FETs in each module.  I am building out the modulator to go a full gallon down the road.


One of those 77000uF capacitors will be sufficient !  I use 64000uF in a kw modulator/power supply.  Definitely use a step start in the power supply to protect the rectifiers and other components from excessive inrush current.
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w8khk
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« Reply #36 on: September 19, 2016, 12:03:19 PM »

Thanks for the tip, Steve.  Yes, I definitely planned to include step-start circuitry.  The transformer does not have a secondary center tap, but it does have two primary windings with taps to allow the use of 120/208/240 mains.  I will switch the windings in series for tune, and parallel for operate, as you did in the class-H modulator schematic.

I am leaning toward a single RF unit for both 75 and 160, rather than two separate units.  From your documentation, I understand the need to switch in more shunt capacity with low-inductance connections on the relays for 160, but I have a question regarding the tuning capacitor.  Your 450 watt 80 meter RF amplifier circuit specifies 20-500 pf for c-tuning, with 5uh L1.  I wonder if you find that you use most of the 500 pf at the low end of 75 meter phone, or if this value capacitor is also sufficient for 160?  Being that the tuning capacitor is one of the largest components in the rig,  I would like to get it sized appropriately when I do the initial metalwork.  I would rather not have to switch in additional C for tuning 160.  Depending upon what components I have, it might be more practical for me to make two separate amplifiers, one for each band.  If I knew the output impedance of the amplifier with two modules of four FETs each, I could calculate the values, but I have no starting point or experience here, and your guidance is appreciated.  I did not find anything on your website that specified the c tuning value needed for 160, and if I understand correctly, your transmitter that switches between these two bands has four FET modules rather than two.  Thanks for your input.
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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #37 on: September 19, 2016, 07:23:36 PM »

I've used 1000pF (or more) for every RF deck I've ever built that covers 160.  You end up using pretty much all of it, particularly at the low end of the band.

In my 1kW rig at Rattlesnake Island, I have a 300pF fixed vacuum cap in parallel with 40-700pF variable.  Keeps the size a little smaller, and works great!

The more capacitance you have, the lower the voltage rating has to be (within limits).  I would not go over 1400pF on 160 and would not go over 750pF on 75 meters.
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« Reply #38 on: September 19, 2016, 07:39:57 PM »

Steve, that information is very helpful, just what I was looking for.  Of course the impedances are much lower with solid state than with vacuum tubes (where most of my experience lies).  And we are working with a series resonant circuit here instead of the parallel resonant circuit common in the tube finals.

The capacitor I planned is definitely too small, but now I know I can build it with the right values to make a dual-band final.  I looked at your photos, and it is very ingenious the way you used braided cable with the shunt relays on 160 meters.  I am still studying all your documentation and photos, and learn and remember more each day.  Thanks again!
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« Reply #39 on: September 26, 2016, 12:50:47 AM »

Oh yeah!  The dipole is up and I'm on the air on 75 meters.  I made the maiden voyage of this transmitter just now and talked with Billy in Tucson, N6YW.  He just piled on the compliments about the audio of this rig, and I don't think he was making it up. 

I took my liberty with old buzzarding, and the heat sink just barely got warm at 350 watts carrier.  I - like - it! 

My thanks to everybody here, especially Steve, for all the help and info to get this rig built.  I've probably clicked on the class E website an accumulated 1000 times, but I got there.

Jon
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« Reply #40 on: September 28, 2016, 05:38:59 PM »

Oh yeah!  The dipole is up and I'm on the air on 75 meters.  I made the maiden voyage of this transmitter just now and talked with Billy in Tucson, N6YW.  He just piled on the compliments about the audio of this rig, and I don't think he was making it up. 

I took my liberty with old buzzarding, and the heat sink just barely got warm at 350 watts carrier.  I - like - it! 

My thanks to everybody here, especially Steve, for all the help and info to get this rig built.  I've probably clicked on the class E website an accumulated 1000 times, but I got there.

Jon

Hey, that's fantastic Jon!!  Nice work !  Looking forward to hearing it.

I don't know if you have one of the R.E.A. modulation monitors, but if you do, make a short transcript file with the rig transmitting (File -> Capture Audio and Modulation Data..)  and send it!  I'd love to hear and SEE the modulation.  If you do, I can post it for anyone who is interested to be able to download and check out.

As the year wears on, it should be possible to communicate between New England and your location at night.  Do this quite regularly to the West coast, and to people in AZ.

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« Reply #41 on: September 28, 2016, 10:57:11 PM »

Thanks!  I'm hoping that I'll be able to hit the east coast with this.  I was 20 over in Idaho a couple nights ago, so things look promising.  My 75 meter dipole is an inverted V sloping dipole.  The apex is about 25 or 30 feet off the ground and the ends are only about 5 feet off the ground.  It's not great, but it's the best I can do at my house. 

I don't have a modulation monitor, but Christmas is coming!  I can throw it into my wish list along with Bose computer speakers... I'm high maintenance. 

I made one final touch to the modulator rack.  I added a Broadcast emblem from a 1950's or 60's RCA broadcast transmitter.  It's kinda cool.

Jon


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« Reply #42 on: September 29, 2016, 12:51:31 PM »

...but, I can't wait for Christmas. I just ordered one!

Jon
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« Reply #43 on: September 29, 2016, 05:11:21 PM »



John,

   I was on the Boat Anchor last night on 3870 from Texas. Definitely some "bad blood" between the Texicans on vintage SSB and the west coast AM'ers coexisting on the same frequency. I was looking for you last night from the Sedona, Az. SDR receiver. There was a huge group of AM'ers in there. Some of the Texan stations were pretty strong your way. The best I could do was make a faint 1 Khz tone if I keyed up on 3871 with 10 watts with my Flex.

Sedona SDR:
  http://w7rna.dyndns-remote.com:18901/

Jim
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ka1tdq
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« Reply #44 on: September 29, 2016, 06:13:23 PM »

Hey Jim

I actually don't get on a whole lot.  But, when I got on a few nights ago, I was in QSO with Joe from Utah.  A sidebander switched to AM so he could talk to us and said that we were on the frequency that they used every night for an SSB group.  Joe said that we were there and wouldn't move.  The sidebander then said that they would talk over us, and the argument ensued from there. 

I made a comment that they were more than welcome to join our conversation by switching to AM, but they decided to move up in frequency.  My guess is that they wouldn't have been able to talk over us anyway. 

This could get fun though!  Maybe a 24 FET rig is the next project?   Smiley  Nah, I've got to go home tonight and put together my kid's backyard playset that just got delivered.

Jon
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« Reply #45 on: September 29, 2016, 09:05:26 PM »

24 Fets would be good, but getting the antenna way up in the air will give you more of a boost !!  It really does make SUCH a difference !
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« Reply #46 on: October 03, 2016, 10:12:43 PM »

Well Steve, I just got your modulation monitor and it works pretty slick!  I did a quick on-the-air check and I'm getting around 135% positive peaks and the negative never seem to get near 100%.  At quick look, the seemed to be limited to 90% or so. 

I'll send you a file sometime this week.  Right now there's an AM net on 3870, but I don't feel like jumping in.  Long story, but I'm tired... Just got home from work and recovering from my kid's birthday party over the weekend. 

Anyway, again, great product!  You sure can't beat the price either!

Jon


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« Reply #47 on: October 05, 2016, 09:18:01 PM »

I made a short YouTube video showing a recorded CQ call using the transmitter.  Carrier power is 400 watts.  The audio is being played by my computer speakers.  Negative peaks never exceed 100% and the highest positive peak is somewhere around 150%.

https://www.youtube.com/watch?v=bp6JwcHdCHs

Jon
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