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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Sun 18, 2021 8:12 pm 
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Macrohenry wrote:
Interesting. Then I need to revise my comment.

The posted photo shows solder pads on the top of the board, apparently so the constructor can choose to surface mount all the components. Given the comparative difficulty of making a uniform solder joint on the top side, why would the manufacturer even give a constructor this choice?

This is how it's done. Soldermask is not placed on thru hole pads, top or bottom. Look at other commercially made boards and you'll see the exact same thing. In fact, if it were placed on the top, you'd need to still have clearance around the thru-hole as you don't want soldermask going into the hole. With registration accuracy limits, you'd need to have a few if not 10 mil clearance. It just isn't done in the industry.


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Sun 18, 2021 8:30 pm 
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tgr131 wrote:
I intended to learn a lot from this project. I had hoped to improve my soldering skills and produce a working project. I ended up learning how to troubleshoot a circuit, and I still suck at soldering :D . Not a total loss, but not exactly what I had in mind!
David

The board has plated thru holes and is HASL finished (hot air solder leveling) and appears to use good old lead solder, not lead free. It's an easy board to solder to.

I'd get the dip packaged oscillator - it has more headroom for max voltage, and again you could tack the 5V zener on it.


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Sun 18, 2021 10:51 pm 
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Quote:
Some of the connections the solder flowed well, and I could see solder had gone through to the top of the board. Others connections, the solder seemed not to want to melt when I brought it to the iron, and when it did, it came off with the iron or clung higher on the lead when I removed the iron. I was running the iron at 330 C.

First of all, your iron isn't hot enough. 626 degrees is for special low-temperature solder. For ordinary 60/40 or 63/37 solder, 750 degrees works well.

You shouldn't be touching the solder to the iron except for a small amount to make a good thermal contact with the pad on the board. The idea is to heat the pad until the solder melts when it is touched to the connection, not the iron.

Keep the iron tip clean.

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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Mon 19, 2021 2:39 am 
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Since all the oscillators will run fine at 5V, a 5.1V or 4.7V zener diode connected across its power pins will give the proper oscillator voltage regardless of input voltage. The only downside is some extra current drain - if run from a 9V battery select the dropping resistor for the particular oscillator used. Maybe we can add the zener in a future revision of the PCB.

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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Tue 20, 2021 4:03 am 
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Location: Ventura, CA
I dragged my SA out to test the HP 606A, and while it was still out I tested this AM TX board. Now I know why it's triggering the squelch on my 70cm ham HT's (440Mhz). Rich harmonics coming from this. I need to make a low pass filter. TX board built with recommended components and fixed inductors.

My SA is too old to have a USB port for floppy drive for saving images. Sorry for the poor picture quality. These are taken with an aerial whip attached to my SA. Vertical scale is 10db/div

900 Khz - 1100 Khz, TX off
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File comment: Transmitter off
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900 Khz - 1100 Khz, TX ON
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File comment: Transmitter ON, 1.00Mhz oscillator, no audio
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900 Khz - 10 Mhz, TX off
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File comment: 900Khz - 10Mhz, TX off
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900 Khz - 10 Mhz, TX ON
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File comment: 900Khz - 10Mhz, TX ON
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900 Khz - 100 Mhz, TX ON
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File comment: 900Khz - 100 Mhz TX ON
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900 Khz - 500 Mhz, TX off
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File comment: 900Khz - 500Mhz TX off
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900 Khz - 500 Mhz, TX ON
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File comment: 900Khz - 500 Mhz TX ON
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image5.jpeg [ 196.25 KiB | Viewed 571 times ]


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Wed 21, 2021 2:42 am 
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A low-pass filter on the antenna may not be enough. At those frequencies the traces on the board are long enough to be reasonably effective antennas. You may have to shield the whole thing and filter all the wires coming out.

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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Tue 27, 2021 3:30 am 
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Greetings, ,

With much guidance from my buddy the electrical engineer, and hwhall's 1544 oscillator, I replaced R4 with a 100 ohm resistor, and ran a 5.1 Zener diode from the junction at R4/C1/C14 to ground.

All is working well in initial tests without an antenna. Thanks for the encouragement and the help getting it working! As always, I have a few questions. I used the Coilcraft Slot Ten 2-14 option. What does the trimmer do? I can tweak it with the alignment tool, but I don't seem to notice any difference.

Also, is the 10 foot coil for the antenna necessary, or can it be shorter?

Thanks for the help everyone.

David


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Thu 29, 2021 7:48 pm 
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Location: Ventura, CA
tgr131 wrote:
I used the Coilcraft Slot Ten 2-14 option. What does the trimmer do? I can tweak it with the alignment tool, but I don't seem to notice any difference.

Also, is the 10 foot coil for the antenna necessary, or can it be shorter?

Congrats David!

The adjustable coil is so you can tune the output circuit/antenna for maximum radiated power at your transmitting frequency. The reason you're not hearing a difference is likely because you have quite a bit of power radiating no matter what the setting is, OR, you need a lot more adjustment for your setup (especially with the shorter antenna). If you have a field strength meter you could visually see if the radiated power is changing when you make your adjustment - you just won't know if you're peaking the fundamental frequency or the harmonics. You could move your radio further way until the signal is weak and then adjust the coil and see if you hear a difference.

Antenna length I don't think is critical. The longer it is, the further you can transmit and vice versa. To stay within FCC rules is the reason they have it at 10' as a max value


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: Apr Thu 29, 2021 8:32 pm 
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You probably don't hear any change because the automatic volume control in your receiver is adjusting to remove the changes. As stated above, move the receiver far enough away so that the signal is barely audible. That way it won't be strong enough to activate the AVC. Or use a receiver without AVC.

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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Sat 01, 2021 4:15 pm 
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Good Morning -

First, probably a silly question -- Do you guys leave the antenna in a loop?

Secon, I'm trying to learn as much as I can off of this project, and my friend suggested I probe with my scope to see what the board revealed. Up front, I bought this scope used, and when I touch the "calibrate" post, I'm not able to see EXACTLY what's described in the manual, but it's close.

I probed with the probe set to 1x, and the scope set to Horizontal set to .5 microSec/cm, and the vertical 5 v/cm and got a nice sine wave:
Attachment:
IMG_5219 (2).jpg
IMG_5219 (2).jpg [ 494.45 KiB | Viewed 370 times ]


I probed a 10x, with horizontal set to .5 microsec, and vertical set to .5 v/cm, and got a little bumpier trace:
Attachment:
IMG_5220 (2).jpg
IMG_5220 (2).jpg [ 500.18 KiB | Viewed 370 times ]


Am I seeing what I should? Any tips on what to check?

Thanks for all your feedback as I try to learn.

David


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Sun 02, 2021 2:58 am 
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tgr131 wrote:
Am I seeing what I should? Any tips on what to check?

Thanks for all your feedback as I try to learn.

David


What are you probing on the transmitter board? With that sweep setting, I'm seeing 1 cycle in about 6mS, or a 166 Hz signal. That's low. Are you probing the audio section?

It's weird that your 10:1 probe signal didn't match the amplitude of the 1:1 probe with the corresponding vertical voltage division change. That said, the 1:1 setting would present more of a load to the signal you're testing, if the signal was high impedance, but I would have expected the sinewave trace for 10:1 and the truncated sinewave for the 1:1, and you got the opposite.


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Sun 02, 2021 3:27 am 
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ai6vx wrote:
tgr131 wrote:
Am I seeing what I should? Any tips on what to check?

Thanks for all your feedback as I try to learn.

David


What are you probing on the transmitter board? With that sweep setting, I'm seeing 1 cycle in about 6mS, or a 166 Hz signal. That's low. Are you probing the audio section

I am seeing 1 cycle in 600 ns or 1670 KHz. That's probably about right without a good shot of the scope screen and without knowing how well calibrated it is.

You say the scope trace isn't correct when connected to the calibration terminal, have you adjusted the probe compensation (only for X10)? Where have you connected the ground lead from the probe? Leaving it unconnected is inviting all sorts of strange displays. Use the shortest ground lead that came with the probe that you can, and connect it to the closest ground on the circuit. And remember, connecting a scope or anything else always disturbs the circuit, the object being to disturb it little enough that you get a good idea of what it's doing. So when you get strange results, sometimes it is your test setup to blame. The higher you go in frequency, the more often you see this.

The antenna should be stretched out. It is generally said to set it vertically but some people report better results with it horizontal. Experiment and see what works best. You may have to retune the transmitter each time you change the antenna.

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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Sun 02, 2021 4:25 am 
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Jim Mueller wrote:
I am seeing 1 cycle in 600 ns or 1670 KHz. That's probably about right without a good shot of the scope screen and without knowing how well calibrated it is.

I think he's on the 5mS/div setting on the horizontal scale. Unless my eyes are deceiving me.

Dave


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Sun 02, 2021 2:50 pm 
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Using 1:1 will add a lot of capacitance; this attenuates harmonics, so it looks more like a sine wave. The 10:1 gives a better view of the signal. The extra capacitance also affects the tuning of the output circuit - if you want to tune for maximum, use 10:1. But it will still detune the circuit to a degree.

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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Sun 02, 2021 7:36 pm 
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Greetings,

Thanks for all the feedback!

* I attached my probe to the antenna out, and the ground was attached to one of the screw holes in the board. I started to poke around, but having no idea where to poke, I realized that there was potential to short something and ruin the circuit. It's working well, so I don't want to ruin it. If you guys could suggest the appropriate points to probe and and appropriate ground so I could see something interesting on the scope, that would be great. I am very new at this. :)

* As someone mentioned, setting the antenna up vertically in increased the range significantly.

* I have found that the sound is crystal clear when the receiver is in 1-3 feet of the antenna. If you exceed that distance, you still get good audio, but an audible hum can be heard in quiet parts (ie, during a news podcast or during a quiet part of a song). It is present on my antique radios or my battery operated Sony. It is not present when the unit is not transmitting, although there's some RFI that can be heard in the neighborhood of that freq. If it's circuit related, any suggestions to improve that?

Thanks for being so helpful to this newb, and I'm enjoying this little transmitter. Hope to built the 1.000 version in a few weeks. It's been a neat project, and I really appreciate all the help I've received here.

David


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Mon 03, 2021 4:05 pm 
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Regarding the audio hum, try running the TX board on a 9 volt battery. If the hum disappears, it's coming from your power supply. If not, it may be an audio grounding issue.

Or, it could be the radiated AM signal getting into nearby AC powered equipment. Mixing of the carrier with 60 cycle voltages in a rectifier circuit can result in a modulated AM signal that is picked up by the on-board oscillator, thereby modulating your carrier.

It sounds kind of fantastic, but I have seen it happen at higher frequencies.

I have noticed that some wall wart supplies seem to be more susceptible to hum problems than others. Be sure to have your antenna located as far away from the supply wiring as possible.

Hope this helps.


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Tue 04, 2021 3:22 am 
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Location: Kingwood, Texas
tgr131 wrote:
* I have found that the sound is crystal clear when the receiver is in 1-3 feet of the antenna. If you exceed that distance, you still get good audio, but an audible hum can be heard in quiet parts (ie, during a news podcast or during a quiet part of a song).


I had hum on mine until I added a ground. That eliminated it entirely. You might want to give that a try.

Darrell


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Tue 04, 2021 8:52 pm 
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hbr nut wrote:
tgr131 wrote:
* I have found that the sound is crystal clear when the receiver is in 1-3 feet of the antenna. If you exceed that distance, you still get good audio, but an audible hum can be heard in quiet parts (ie, during a news podcast or during a quiet part of a song).


I had hum on mine until I added a ground. That eliminated it entirely. You might want to give that a try.

Darrell


Greetings -

I've got this running off a 9V battery, and still have the hum. How do I add this ground of which you speak? Is it something you add to the circuit, or the antenna?

Thanks for your patience with my questions.

D


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Wed 05, 2021 6:08 pm 
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Location: Kingwood, Texas
You can connect it to the negative side of the 9 volt battery. Iā€™ve tried connecting mine to a ground rod, the shield of my cable TV and the ground pin of an AC receptacle. In my case, each of them eliminated all traces of hum.

Darrell


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 Post subject: Re: Antique Wireless Assoc. AM tx board
PostPosted: May Wed 05, 2021 9:17 pm 
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Location: Ventura, CA
tgr131 wrote:
I've got this running off a 9V battery, and still have the hum. How do I add this ground of which you speak? Is it something you add to the circuit, or the antenna?

Thanks for your patience with my questions.

D


Is this happening with more than one radio?


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