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Homebrew transmitter progress updates




 
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W8ACR
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« Reply #100 on: April 28, 2013, 01:13:03 AM »

Update#16 - Buzzard Baby has assumed her position in the hamshack. Electrically, she's complete. I might tweak a few things here and there as time goes by, but she works like she's supposed to. I have transmitted into a dummy load and both the RF and audio seem to be working well. Cosmetically, there are a few things I want to do to dress her up a bit, but so far I'd say she a beaut.

Maiden voyage will be Sunday afternoon. +/- 7290 kHz. Around 2PM or so (Central time).


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« Reply #101 on: April 28, 2013, 09:37:50 AM »

Looks wonderful Ron!  Won't be able to hear you on 40M at that time of day but I am sure you will find  someone to have that first QSO with. 
73,
Joe, GMS
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« Reply #102 on: April 28, 2013, 02:26:31 PM »

OK Joe,

Will wait until about 7PM central time, and will probably drop down a bit in Freq to avoid the 7290 broadcast station. Listen between 7275 and 7285. Hope QSO#1 is with W3GMS.

Ron
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« Reply #103 on: April 28, 2013, 05:38:18 PM »


Ron,

  I will be tuned up and listening from Texas. Maybe I can be #2.. Cool. Sometimes 7295 is open too.

The attachment shows a modulator very similar to yours where the distortion between the driver and the modulator combined is plotted. If I read the graphs right, you should get around 3% THD plus whatever the low level stages might add. Still, without NFB, this rig should sound pretty decent. I would still try to balance out the push pull excitation from the 6N7, and maybe try NFB later down the road if you want.

Jim
WD5JKO


* 811_Modulator1.jpg (537.81 KB, 1600x2696 - viewed 723 times.)
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W3GMS
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« Reply #104 on: April 28, 2013, 06:52:46 PM »

OK Joe,

Will wait until about 7PM central time, and will probably drop down a bit in Freq to avoid the 7290 broadcast station. Listen between 7275 and 7285. Hope QSO#1 is with W3GMS.

Ron

Sound great Ron.  That would be 8PM EDT here on the East Coast.  Hopefully propagation will be good.
73,
Joe, GMS   
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« Reply #105 on: April 28, 2013, 08:00:15 PM »

Almost 7PM. Two AM QSO's right now on 7287 and 7295. Will wait for a break in the action. She's all tuned up and ready to go.

Ron
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« Reply #106 on: April 28, 2013, 08:01:47 PM »

Ron,
7.295 is being vacated soon.  7.275 thru 7.285 sounds very busy with SSB.  The locals here are pretty strong so not sure how good longer propagation will be.  We could try again around 10PM Eastern which would be 9PM Central time.
Joe, GMS  
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« Reply #107 on: April 28, 2013, 08:08:47 PM »

Hi Ron,
I am on 7.295 right now talking with Jerry-W1ZB and Dave-WB4IUY.  Will be listening for your between transmissions.
Joe, GMS
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« Reply #108 on: April 28, 2013, 09:05:10 PM »

Hi Ron,
It looks like a foreign BC station got us!  Very loud signal on 7.295 but it was wonderful working you with your new rig!  I really enjoyed the QSO and congrats for building a great rig. 
73,
Joe, W3GMS
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« Reply #109 on: April 28, 2013, 09:44:58 PM »

Hi Ron,
It looks like a foreign BC station got us!  Very loud signal on 7.295 but it was wonderful working you with your new rig!  I really enjoyed the QSO and congrats for building a great rig. 
73,
Joe, W3GMS

  I was tuned up and ready to go here. There was a AM QSO further west on 7292 that was about 10db stronger then you guys on 7295, and then at 7:55 pm CST the foreign broadcast station came on 7295. So my thoughts of joining in ended suddenly.

  It seems that you guys had some fun though, and what I did hear from Ron sounded good.

Jim
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« Reply #110 on: April 28, 2013, 09:45:11 PM »

One thing that could be done with the gray colored Lamba power supply is to flip the front panel around and paint the blank side black to match the rest.
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« Reply #111 on: April 28, 2013, 10:14:48 PM »

Hi Ron,
It looks like a foreign BC station got us!  Very loud signal on 7.295 but it was wonderful working you with your new rig!  I really enjoyed the QSO and congrats for building a great rig. 
73,
Joe, W3GMS

  I was tuned up and ready to go here. There was a AM QSO further west on 7292 that was about 10db stronger then you guys on 7295, and then at 7:55 pm CST the foreign broadcast station came on 7295. So my thoughts of joining in ended suddenly.

  It seems that you guys had some fun though, and what I did hear from Ron sounded good.

Jim
WD5JKO

Thanks for listening in Jim.  We had a good hour or so QSO and it was good to hear Ron on his new HB Rig.  Yes, the foreign BC station on 95 was very strong at my QTH and that pretty much ended the QSO.  I did QSY down to 90 and gave Ron a few calls but I don't think he was listening down on 90.
Joe, GMS
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« Reply #112 on: April 29, 2013, 10:55:34 PM »

Ron
Nice sounding rig.  Steve KL7OF and I were listening from Terry MT.  Called you but foreign BC was too much for the barefoot 706.
Camping in the badlands, prairie dogs beware. 
Bob ka7woc
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Bob (aka Boatyard)
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« Reply #113 on: April 29, 2013, 10:59:27 PM »

Update #17 - 4/29/13 - Don't like what I see here on the o'scope. The first pic shows the signal from the HP200 audio oscillator, proving I was injecting a nice sinusoidal audio signal. The second pic shows the transmitter output at 1000 Hz and the third pic shows transmitter putput at 100 Hz. I've got plenty of audio. I can easily overmodulate the carrier. These readings were taken at about 300W input to the RF section. Comments? Solutions?

Ron


* update 4-29-13 002.jpg (132.76 KB, 640x480 - viewed 699 times.)

* update 4-29-13 003.jpg (119.81 KB, 640x480 - viewed 687 times.)

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« Reply #114 on: April 29, 2013, 11:03:16 PM »

Hi Bob,

Good to hear from you. Please see my post above. Did it really sound good? 'cause if it did, I won't worry too much about what I see on the scope.

Ron
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« Reply #115 on: April 29, 2013, 11:19:37 PM »

Ron,

It's a good start, OM.

Looks like some non-linearity in the trapezoid pattern.  This may show up as some side splatter. Run the same tones thru and listen on your local receiver with a 6" wire ant stub.  Do you hear one tone on freq or is there a whole bunch of them going up and down the band? (IE, 2nd, third, forth harmonics)  How far down in dB are these audio tone harmonics from the carrier?

Better yet, you need to go beyond a simple scope.  Get a $25 used Softrock and set up a simple spectrum analyzer using the free Flex software on your computer.   Run some tones and test for THD and IMD - get some real numbers and data to compare and create a baseline.  You will then be able to make ongoing adjustments and find the best settings on your rig for the cleanest signal.

This is where the hard part starts after building the rig - getting it all dialed in and optimized.  Get your own software spec anayzer test set up going and you will always know exactly how clean your rig really is - and make deeper improvements that are way beyond a scope pattern.

This is the perfect time to start playing with audio negative feedback and considering some of the ideas Jim /JKO suggested about the driver stages.  In some time, you will look back and see that trapezoid pattern as straight as a razor blade, caw mawn.


I'll be going thru this same testing over the next few weeks myself. We can compare notes.

T

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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #116 on: April 29, 2013, 11:47:18 PM »

Uh Oh Tom,

You're asking for a lot. This SDR stuff is new territory for me. Which Softrock should I look for, and where do I get it? I have zero knowledge of this stuff.  Embarrassed

I did some investigating, and the "folded" patterns as seen above may just be a phase shift artifact introduced by the coupling from transmitter to o'scope, and is of no concern. However, I will do the simple tone test that you recommended.
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« Reply #117 on: April 30, 2013, 12:06:23 AM »

Ron,

It may be that your final doesn't have the emission ability for full modulation "absorption". Sad

I've seen tubes that did fine on CW, but exhibit the same characteristics as you have there.

You might try upping the filament a bit and see.

I have two of those bottles in the box for you now, will send ASAP.

73GD
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« Reply #118 on: April 30, 2013, 12:51:49 AM »

Ron,

Yes, half the battle is putting together a testing system that can be depended on.  Many times I have run tests and found the test set up itself was giving me erroneous data.  

Do you have a good ricebox you can use for the trapezoid test on ssb?  That shud produce a pretty straight trap if it is near the normal  -30db 3rd IMD and tell you how good the setup is.

For a Softrock, put out a "wanted" here on the BB.

A Softrock is not as difficult as you think to master.  Getting out of our comfort zones can yield big returns sometimes...  Wink  You cud have one up and running in an evening.  Plus, in addition to the spec analyzer, you'll have a sync detector - and a super high fidelity receiver second to none.  I'll bet there are a few guys with a complete board (cheap) willing to sell, that have moved up to a Flex or whatever.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #119 on: May 01, 2013, 11:39:31 PM »

Ron
Steve and I both thought you sounded great.   Until someone says otherwise work it full scrote.   
Ka7woc & kl7of
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Bob (aka Boatyard)
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« Reply #120 on: May 09, 2013, 12:18:43 AM »

Have made several contacts on both 40 and 75 meters, and have gotten good reports. Conditions overall have not been great, but Monday night on 75 was pretty good. Had a roundtable QSO with K4KYV inTN, W4BVT in VA, KD0ZS in WY and WA3QGD in WA. My antenna was a 32 ft vertical with a loading coil at the base.

Early returns are promising. Will try to get the 260 ft dipole up soon.

Ron
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« Reply #121 on: May 09, 2013, 12:34:09 AM »

Ron.......When we heard your initial transmission on 40 meters...you sounded very good.....Bob and I were camped  in a prairie dog town in the Badlands ....Using a loaded ground mounted whip with radials and  an Icom ricebox....congrats....Steve
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« Reply #122 on: July 11, 2013, 04:52:11 PM »

Last two

Ron,

You draw schematics the way I do, the old  fashion way.  Nothing looks better to me than a clean hand drawn schematic with the flow and proportions correct.  Very nice job and I look forward to working you even under better conditions some night next winter on 40M.  I got my line noise issue fixed, so I can hear much better now. 

73,
Joe, W3GMS   
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« Reply #123 on: July 12, 2013, 03:23:03 AM »

The middle pic's 3D look may alternately be some RF leaking into the CRT's AF side and is phase shifted slightly from that on the RF plates. Hi-Z elements there on a CRT or scope inputs.

The bottom pic looks like modulator crossover distortion?
If the driver is push pull it could come from there or from the power stage.

Maybe try troubleshooting without the RF & with a proper large resistor load on the modulator.

Or, just run DC through the final to act as the load, presuming you have enough dissipation capacity in the final tube.

That way you can vary the load resistance seen by the modulator by varying the DC current drawn by the RF stage.

varying said current can be done via the RF stage bias adjustment, including positive bias if the RF stage is a zero bias tube as well and you respect its grid dissipation.

It may sound weird but this test method simulates the behavior of the RF stage as a modulator load decently well for modulator troubleshooting work.

- just opinions. I have used this method before with a 4-1000 final (2500VDC@200-300mA) but it ought to scale just fine. Will be doing it again soon as some feedback needs applied to help Mr. Tucker's modulator; that will be an experiment allright.
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« Reply #124 on: July 20, 2013, 12:11:23 AM »

I'm reposting the schematics for Buzzard Baby from a different computer so that they may be viewed more easily - not that they are of great interest to anybody. Nothing fancy here, it's all  pretty basic 1940's amateur transmitter technology. The only significant departure is the silicon diode rectifier in the bias supply (should have used a 5Y3), and the use of a pi network final tank instead of a swinging link.

Final amp is typically run at +2000VDC and 250mA. Carrier is typically at about 370-380 Watts output. I can independently vary the final plate voltage by using an 18A variac on the primary of the plate transformer. Modulation is by modified Heising system using a 50H Dahl reactor. Plate voltage on the modulators is about +1350VDC. RF and modulator plate supplies are separate. Modulators are 811A's with -2.4VDC bias from two rechargable NiCad's. Driver transformer is UTC S-9 3:1 step down. Mod tranny is UTC S-22 set for about 16000 ohms primary and 9600 ohms secondary. Mic is a Heil Classic via a W2IHY preamp. PLENTY of audio, can easily modulate near 100%. Reports have been good so far, but conditions continue to be poor and I've not yet been on the air on a quiet night. RF exciter is a Johnson Viking 1. The whole thing plugs into a 120V/15A wall socket. No blown breakers yet, and new heftier house wiring is coming soon. Both RF and modulator plate voltage is left ON during standby, but speech amp plate voltage and RF excitation are OFF during standby. Speech amp plate voltage is +300VDC from a Lambda 0-324 regulated PS.


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