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AMT-5000 problems peaking RF output

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AMT-5000 problems peaking RF output

I am now even more frustrated than I can possibly describe in a polite manner. I've tried everything I can think of plus what has been suggested. No matter what I do I get 0.144v when measuring RF input current, and 2.688v when measuring RF input voltage. This is across the entire range of  Based on the formula this means the transmitter is putting out less than 4 mw (0.0387072). I get this value across the entire range of tuning C1.  As Carl suggested I confirmed that S1 was not connected (it never was). I powered off the xmtr during every change just to be safe to the transmitter.  I tried the RF peaking procedure using  each of the three jumper positions suggested by the manual (S8,S9,S10). Same results.  I also replaced this jumper with a brand new one in case the first one was bad and again went through the peaking procedure using all three jumper positions again. Same results. I inserted a capacitor in the antenna line. I went from feeding the coax to just a long wire again. I changed from using my cheapo Extech VOM to my Fluke 110 DMM. I also tried adjusting c25 to see if the readings changed. They did not. BTW I still don't get why the manual says to keep the slot of C25 lined up front to back but since you can rotate this cap several times the manual doesn't mention how many turns up or down this cap should be rotated when the slot is lined up front to back.  Two days ago I was getting the best range ever even getting over the mountain  behind my house.  Now I don't even get down to the end of my driveway (800ft).. If you can see it on the attachment, that longes red line was over 9000 feet. How it got over the mountain and I could hear it baffles me, but anyway that was 2 days ago, not now.  Any ideas?

carl AvatarApr 18, 2017 16:14:26 GMT -4 carl said:Oh, That's Right, the CoaxOver the course of the back and forths I lost sight of the coax and wasn't sure it was still in place or not. Now that we know, I'm guessing that all that coax is swamping the signal with capacitance that is throwing it out of the designed range. By adding a 20 pF or other small value of capacitor in line with the antenna you might be able to get the tuning back into range.

 

??

... I went from feeding the coax to just a long wire again. ...

Most likely the SSTran AMT5000 was not designed to use some random length of 50 Ω coaxial cable between its r-f output connector and a ~ 3-meter conductor, or to a "long wire" conductor considered to be the antenna.

Presuming that the assembled transmitter meets its design specs, you might have better success if you strictly follow the installation configuration and adjustment sequence given in the documentation supplied by the manufacturer of that transmitter.

Rich,

Rich,

Thanks but this is exactly what I did (follow the manual).  I have tuned this xmtr over a dozen times as I changed configurations such as adding more radials, and had no problems.  Two or three days ago the xmtr was working better than ever. The problem only started yesterday when I went to re-peak it after adding a ground. 

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

Problem

Jim,

The first rule of troubleshooting is to check the power supply voltage so this is where to start.

Something has changed, most probably a component is damaged.  I have no experience with the AMT-5000 but I do have experience with tuned transmitter outputs.  When prototyping my transmitter I began using FETs and found  that under certain load and tuning conditions the drain to source voltage exceeded the device rating (60 Volts in my case).  I am suggesting that you check the FETs at the output stage by measuring the drain to source resistance.  Not having the schematic I cannot predict what is normal for this measurement but maybe someone else with a working transmitter can make this measurement and give a typical value.

Neil

 

2nd Opinion

My guess is that so much metal is hung on the RF output end of things, antenna and ground lines included, that the tuning range on the manual's chart is way out of bounds for what the transmitter is designed to handle.

Keep in mind that the antenna, radials and ground are 150-feet away from the transmitter.

The design is very particular about expecting a 30 pF antenna load under ordinary Part 15 conditions.

Carl Blare

Jimhenry,

Jimhenry,

To check the AMT5000, you can simulate a load by connecting the transmitter to a 33pf capacitor in series with a 47 ohm non inductive resistor.

Does the transmitter now tune up correctly ?

Paul.

Small Potatos

BOARDMAKER suggests using a dummy-load:  "33pf capacitor in series with a 47 ohm non inductive resistor."

The information I have from a previous posting by PhilB, inventer of the AMT5000 and 3000, is that 30pf capacitor and 30 ohm non-inductive resistor can be used to simulate an antenna with either transmitter.

I tried to find that original posting by PhilB on this website but have not been able to locate it, given the inability of the "search tool" to find most things.

If someone else can link to that post it will be useful.

Carl Blare

Carl,

Carl,

The capacitor/resistor values are not critical in value.

47pf and 50 ohm will also tune just fine.

The AMT5000 was designed to tune up with  varying coil loss and ground loss within certain limits.

I have tuned my amt5000 fine with 33p and 50 ohm values.

For instance a i have a 50 ohm dummy load with built in watt meter, connecting the amt5000's output in series with a 33pf capacitor to the said wattmeter tunes up fine.

Paul.

No Doubt

BOARDMAKER is correct.

The flexibility built into the output tuning for AMT5000 covers a range of settings and the dummy load he describes is within that range.

Carl Blare

Everyone, thanks all for your

Everyone, thanks all for your help.  I made the dummy load and the transmitter now peaks just fine. So now I believe the problem is somewhere in the coax, which is going away shortly anyway.

\Jim

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

 'I made the dummy load and

 

'I made the dummy load and the transmitter now peaks just fine. So now I believe the problem is somewhere in the coax, which is going away shortly anyway."

Jim,

I can understand not wanting to put the transmitter outside even in a weather proof cabinet, but you are going to see much better performance out of the transmitter if you can construct the antenna system with the transmitter close to the antenna.

More power will be delivered to the antenna if the path the RF follows is shortened which you already know this. I feel like you will see much better results and gain that coverage you saw a few days ago.

p.s. the image of your coverage map was pretty small, hard to see.

 Barry of Blue Bucket Radio 1620 AM  - http://bluebucketradio.com - WQYY 664

AMT-5000 installation

Barry,

I completely agree and that has always been the final plan.  My current issues are getting the audio and power 150ft. to the transmitter. I'm considerial solar but I might run an aerial power feed on my strand and drop it down to the xmtr. As for the audio, I need to source the right cables to get the audio 150 ft. from my server to the transmitter, and probably an audio amp.

Thanks.

Jim

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

blutooth audio

to get the audio out there you could try blutooth. You can buy a blutooth adapter on ebay for cheap and plug that right into your audio input at the transmitter. 

Isn't Blue Tooth limited to

Isn't Blue Tooth limited to about 30 feet?

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

that was the original

that was the original intention but line of site matters a lot and it can go a lot further in your yard if you have no  bushes etc.  There are also high powered blutooth adapters with longer range. 

https://www.kanda.com/products/Sena/PARANI-UD100-3.html

To get really long range you would go with WIFI instead

Wired for sound

"I need to source the right cables to get the audio 150 ft. from my server to the transmitter, and probably an audio amp."

I think you could use ethernet cables to deliver both audio and power to the transmitter without losing audio quality. This can be bought in bulk or rather in a box of 300 feet or more. Well i don't know why i am explaining how you can buy the box of cable, you have experience in the networking field lol

Anyway, the Chez Procaster if i am not mistaken , uses ethernet cable to deliver power and audio to the transmitter at a remote location. There is other ways, i like the idea of solar for the power and perhaps one of the audio/video senders which work best at line of sight.

The options are endless, your creative juices will go wild with all of the different ways to feed the transmitter.

Have fun with it.

 Barry of Blue Bucket Radio 1620 AM  - http://bluebucketradio.com - WQYY 664

Bluetooth audio

The Bluetooth device here looks interesting, but the audio output on my PC is a 3 mm phone plug, not usb, and I don't know how I'd redirect the audio output to a usb port.  Then on the transmitter, the AMT-5000 , there is no bluetooth nor usb port either, so I have no idea how I could bring the audio into the transmitter.

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

About USB Audio Output

ONLY when a USB audio device is detected by the computer operating system will a new choice appear on the list of available audio outputs.

For example, if the main audio program is Zara, the Audio Output Setting will show the list of output choices.... and USB Audio Out will be on the list, put there by the USB audio device attached at a USB port.

TROUBLE IS, if you set Zara to point its output to the USB Audio port, the output will be switched away from whatever it was pointing to before, which might inlcude needed paths like local monitoring, signal processing or stream encoding.

As with anything there is a solution... using "Virtual Cable" to distribute the audio to all desired points... but this raises the complexity to the degree of periodic confusion trying to figure out where the audio went (things change sometimes all by themselves no one knows why).

Carl Blare

Blue tooth

Even so, how do I get the audio into the 5000? 

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

You've basically got 3

You've basically got 3 choices:

1.  CAT-5 cable (networking cable, preferably shielded).  Long runs of 150 feet should be fine (I've had a run of about 125 feet with no problems).

2.  RF.  You can use a video sender, as suggested, or a Part 15 FM transmitter (although 150 feet is close to the limit for a good signal with the latter)

3.  Wireless streaming.  You can use an Internet radio, or for a more complex, expensive (and reliable) solution, a Barix box.

#1 is the simplest and probably the cheapest.  Plus little can go wrong with cable (compared to the electronics in the other solutions, anyway).

Complete Instruction for Choice # 1

As a service of the ALPB we have detailed a complete step-by-step instruction for building a professional audio transmission line to connect studio with transmitter at a distance of 150'.

Find it at the ALPB Forums in the Transmitter column titled: AMT5000 Questions.

Carl Blare

Thanks

Thanks

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

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