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 Post subject: SSTRAN AMT3000 Output impedance..
PostPosted: May Mon 28, 2018 5:05 pm 
Member

Joined: Dec Mon 17, 2012 5:09 pm
Posts: 61
Location: Quebec City, Canada G2E5S1
Hi list,
I'm about to build a small push-pull RF amplifier
to boost a little my AMT3000 transmitter output.
See both attached schematics. One is the Push-pull RF amp
I'm about to build and the other is the actual AMT3000 output stage..
I chose to use 1280khz as a working frequency in my neighbour.
Here in the province of Quebec there are about no AM stations
since the 80's so the choice is easy.
At that frequency, keeping only L4 (56uH) tuned with C5
I found that the output impedance was around 270 ohms.
(The RF voltage swing at connector J4/P4 goes down halfway with that resistive load).

And by the way all of these will be mounted in my basement.
No outside stuff.

Here are my questions:
- So to keep things nicely balanced my AMT3000 output
connected to my boost RF amplifier should 'see' an input transformer primary
that shows around 270 reactive ohms or little higher right ?

- And since the original AMT3000 has a 270 ohms output impedance
(L4 & C5 tuned at 1280khz) Should I design the boost amplifier
to have the same output impedance ?? I saw MANY RF amplifiers
use 50 ohms antennas, but these are way above my 1800khz range.

My antenna will be made of a 5/8" copper pipe 6 meters long
that will be bent in a 'Z' shape with 2 x 90degs knees in the middle
to accomodate the lack of height (8' ceilings) ,
connected in series with a loading coil. And the final amplifier
will be grounded using a copper rod inserted in my basement's
concrete floor close to the amplifier.
I know this is not at all a 'standard' way to do these things
but believe me this will be the best way for me to have an inside
setup that will generate a 'no static back ground noises' signal
for all my house vintage radios.

I need your help.
Thanks.


Attachments:
AMT3000 output stage.jpg
AMT3000 output stage.jpg [ 116.9 KiB | Viewed 659 times ]
Push-pull RF amplifier.gif
Push-pull RF amplifier.gif [ 2.82 KiB | Viewed 659 times ]
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 Post subject: Re: SSTRAN AMT3000 Output impedance..
PostPosted: May Wed 30, 2018 3:40 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 9505
Location: Santa Rosa, CA
Quote:
My antenna will be made of a 5/8" copper pipe 6 meters long


Maybe in Canada, but not in the USA. FCC Part 15.

Rich


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 Post subject: Re: SSTRAN AMT3000 Output impedance..
PostPosted: May Wed 30, 2018 4:14 pm 
Member

Joined: Dec Mon 17, 2012 5:09 pm
Posts: 61
Location: Quebec City, Canada G2E5S1
I've changed my mind about a copper pipe antenna..
I will do some tests using loop antennas.
It is supposed to be less 'grounding rod' dependant
as far as efficiency is concerned..


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 Post subject: Re: SSTRAN AMT3000 Output impedance..
PostPosted: May Wed 30, 2018 4:55 pm 
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Joined: Jun Sun 22, 2008 2:03 am
Posts: 1335
Location: Burke, VA
Quote:
Maybe in Canada, but not in the USA. FCC Part 15.

Definitely neither in Canada. Annex B.2 of Industry Canada RSS-210 is exactly the same as FCC Part 15.

Quote:
B.2 Band 510-1705 kHz

Devices using this band shall comply with one of the following requirements:

a. The total input power to the final radio frequency stage shall not exceed 100 mW, and the total length of transmission line, antenna and ground lead (if used) shall not exceed 3 m.

b. The field strength of radiated emissions shall not exceed 250 µV/m measured at 30 m

c. Transmitters that employ a leaky coaxial cable as a radiating antenna may meet the field strength limit of 15 µV/m, as measured at a distance of 47715/(frequency in kHz) m (equivalent to wavelength/2π) from the coaxial cable.

d. Emissions outside of this band shall be attenuated by at least 20 dB below the mean transmitter output power, or to the general field strength limits specified in RSS-Gen, whichever is less stringent.

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Binh


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 Post subject: Re: SSTRAN AMT3000 Output impedance..
PostPosted: May Wed 30, 2018 8:07 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 13249
Boo Hoo, I ran a Ramsey AM-25 @ 3/4 watt into the phone line for over a year, no one ever complained..

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Tom


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 Post subject: Re: SSTRAN AMT3000 Output impedance..
PostPosted: Jun Mon 04, 2018 4:17 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 22512
Location: Somers, CT
Thread was locked because it is board policy not to allow discussions regarding equipment that exceed US FCC part 15 regulations, and the fact that this also exceeds Canadian limits.

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Just because it can be done doesn't mean it should be done.


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