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Post by jimhenry2000 on Feb 16, 2017 6:58:54 GMT
So my question for others who own an AMT-5000 is, I want to connect a 102" whip antenna to the transmitter via 50 ohm RG-58 coax. Can I just connect the center conductor to the 5000's antenna terminal and then connect the coax shielding to the 5000's ground terminal? Is the 5000 already matched to an antenna with 50 ohms impedance? Anything else I need to do?
Thanks.
Jim
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Post by End80 on Feb 16, 2017 9:41:27 GMT
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Post by Deleted on Feb 16, 2017 15:49:47 GMT
Jim Henry's question: "Is the 5000 already matched to an antenna with 50 ohms impedance?"
The AMT5000 is not designed to match to 50-ohms.
50-ohms would be typical for a proper AM antenna at 1/4 or 1/2 Wavelength, but the transmitter designer, in knowing that the AMT5000 would feed a grossly under-sized (3-meter) antenna, the output impedance anticipates the severe mis-match presented by a short antenna, and has a more appropriate output impedance.
My guess is that RG-58 transmission line will probably work in your setup, but there may be a more appropriate type of coax under the circumstances. Ask Neil Radio8Z at part15_us.
The length of the transmission line will have an affect on the tuning of the transmitter to match the sum of the antenna + the coax.
There might be some germane links on this subject... if I can find them I will add them to this thread.
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Post by jimhenry2000 on Feb 17, 2017 1:23:57 GMT
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Post by jimhenry2000 on Feb 17, 2017 1:27:13 GMT
Thanks Carl. The 5000's manual seems to be 99.9% focused on assembly, not operation. Jim Henry's question: " Is the 5000 already matched to an antenna with 50 ohms impedance?" The AMT5000 is not designed to match to 50-ohms. 50-ohms would be typical for a proper AM antenna at 1/4 or 1/2 Wavelength, but the transmitter designer, in knowing that the AMT5000 would feed a grossly under-sized (3-meter) antenna, the output impedance anticipates the severe mis-match presented by a short antenna, and has a more appropriate output impedance. My guess is that RG-58 transmission line will probably work in your setup, but there may be a more appropriate type of coax under the circumstances. Ask Neil Radio8Z at part15_us. The length of the transmission line will have an affect on the tuning of the transmitter to match the sum of the antenna + the coax. There might be some germane links on this subject... if I can find them I will add them to this thread. |
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Post by jimhenry2000 on Feb 17, 2017 1:47:59 GMT
After looking at that thread I see it is about the 3000, not the 5000. It is well known that the 3000 requires circuit modifications to use a 50 ohm antenna, but in the past I have read (somewhere) that is not the case for the 5000. |
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Post by End80 on Feb 17, 2017 3:55:47 GMT
Oh, your right. Sorry.
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Post by Deleted on Feb 17, 2017 4:14:31 GMT
A Paragraph from the Maker of the AMT5000
In 2011 when I was first learning how to match my AMT5000 to my antenna I ran into problems because the capacitance of my setup was far lower than would accept proper tuning...
Here is a paragraph from an e-mail from PhilB, the manufacturer:
Antenna capacitance is very important. The tap points suggested in the manual for various frequencies assume the antenna capacitance is in the 25 pf to 30 pf region. This will be true for the 118" white antenna wire, a 102" stainless steel whip, a 1/2" or 3/4" copper pipe a few inches less than 118".
Attach the black wire to anything grounded on your bench or connect it to the (grounded) screw on an AC outlet.
My situation was especially unique because I wanted to load up the metal window frame with attached wires to place the vertical 3-meter antenna length actually within a rear-wall which contained stucco wire mesh thus drastically adding capacitance.
The solution for me was to add a 20 pf capacitor in line (series) with the antenna wire coming out of the transmitter.
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Post by jimhenry2000 on Feb 17, 2017 4:44:51 GMT
Carl, Here is what I was told a few months ago in another forum: "I have both the 3000 and the 5000. Where the 5000 is superior to the 3000 is in its ability to adjust to just about any antenna by a simple internal adjustment. With the 3000, building a base-loaded coil antenna is an ordeal that requires modification to the circuit, then checking for the correct tap on the base coil, lastly adjusting the antenna." I will have to go through the manual again to see what I missed about this "adjustment". Your email from Phil now adds great food for thought... A Paragraph from the Maker of the AMT5000In 2011 when I was first learning how to match my AMT5000 to my antenna I ran into problems because the capacitance of my setup was far lower than would accept proper tuning... Here is a paragraph from an e-mail from PhilB, the manufacturer: Antenna capacitance is very important. The tap points suggested in the manual for various frequencies assume the antenna capacitance is in the 25 pf to 30 pf region. This will be true for the 118" white antenna wire, a 102" stainless steel whip, a 1/2" or 3/4" copper pipe a few inches less than 118".
Attach the black wire to anything grounded on your bench or connect it to the (grounded) screw on an AC outlet.
My situation was especially unique because I wanted to load up the metal window frame with attached wires to place the vertical 3-meter antenna length actually within a rear-wall which contained stucco wire mesh thus drastically adding capacitance. The solution for me was to add a 20 pf capacitor in line (series) with the antenna wire coming out of the transmitter. |
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