Viewing 7 posts - 1 through 7 (of 7 total)
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  • #2313
    Ed Stone
    Forum Participant

    I was getting more and more fed-up with available programming on the Broadcast Band local to Vancouver at certain times of the day – only one station playing any sort of music that I could listen to without cringing (and then not all of the time) and most of the rest being ‘talk radio’, 90% of which is inane sports coverage. I therefore decided to try out a low-power AM transmitter. After some scouring my collection of schematics for a suitable home-brew design (I had made one of these years ago with limited success), eg. https://www.techlib.com/electronics/amxmit.htm, and the various radio forums and websites to see what was available commercially, either ready-made or as a kit, I decided to purchase a kit from SSTran (https://www.sstran.com/). This company, based in the US, have been selling their low-power AM transmitter for a number of years and the reviews I read were all good. They only produce one product, the AMT3000, which has a maximum input power of 100mW. The advantages of this particular kit as I see it are: it comprises all high-quality components, has a high-quality silk-screened PCB, proven track record of success, highly-stable frequency control (phase-locked loop) and carefully-designed audio, modulation and power supply circuit elements. If you are looking for a change to the AM programming in your area I would recommend buying this or a similar piece of kit (there are several others available from other sources, eg. the BC100, a relatively simple crystal-controlled design, the MW-250, a crystal-controlled tube-based design, and various kits made by Ramsey, such as the AM1C).

    I built the AMT3000 kit in around two hours without rushing anything and had no problems with its construction. It worked first time and I managed to select the desired frequency in a quiet spot on the Broadcast Band and tuned-up into its short wire antenna as per the instructions without issue. Using a 3m length of wire as an antenna I have found the signal to be fine anywhere in the house, but quickly disappears into the noise once outside (which is just what I wanted).

    The unit has adjustable gain, modulation depth and compression controls on the front panel and I checked their operation by attaching a scope to the antenna and feeding a tone into the audio input. I can confirm that they all worked as expected, with 100% modulation depth obtained at around 70% rotation of the modulation control. The audio quality is very good with the modulation set at around 90% and applying a small amount of compression (it can be adjusted from 1:1 through 1:5). The transmitter has a switchable treble-boost and various options for dealing with any modulation hum if if occurs (I have had no problems in this regard).

    As for programming, I simply fill-up my iPod with around 1,800 tracks, put it in ‘shuffle’ mode, place it into its mini-dock and feed the audio output into the AMT3000 input and leave it switched on when I am in the house. Now I can just tune into this ‘station’ anytime on any radio in the house and listen to a selection of music that I know I will like when the regular broadcast stations are pumping out commercials, infomercials, sports gibberish and ‘musak’. I also record internet radio programs (eg. see https://radiotime.com/Index.aspx for selection of these) and download (free) ‘oldies’ programming (plays, comedy and the like) on my computer from websites such as https://www.oldtimeradiofans.com/ and the BBC iPlayer website (https://www.bbc.co.uk/iplayer/radio – though you will need a UK IP address to do this – try https://www.my-private-network.co.uk/) – all can be played through the AMT3000 without any difficulty I suggest you use something like ‘Simple Radio Recorder’ (https://www.dennisbabkin.com/php/download.php?what=srr) to record internet radio programs on your computer as mp3 files – this (free) program also has a timer to allow recording to start/stop when you are not around (great for recording ‘Coast to Coast’ on CKNW). Of course you can also play mp3s or other music files from your computer, CDs, vinyl, shellac from your HiFi system or whatever you want! I am using a four-input composite video switch-box (bought from a thrift store for a couple of bucks) to conveniently switch between different audio sources.

    I have never listened to my AM radio collection more than I have in the last few weeks!

    Ed

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    #2318
    Ed Stone
    Forum Participant

    I would just like to add that I am currently listening to this transmitter on a restored RCA AR88LF on its widest bandwidth paired with a 10" Hallicrafters cabinet speaker – sounds wonderful – FM quality on an AM radio!

    Ed

    #2366
    Keith-RL
    Forum Participant

    I built a one tube transmitter a few years agog and it worked great, I could pick it up almost 1/2 mile away on my trucks radio. Nothing fancy construction wise, I used a sixties radio chassis for the project box and junk I had laying around.

    #3323
    Ross Gordon
    CVRS Member

    hi Used to transmit music myself back in the 70’s used a local oscillator 6BE6 stuck an antenna on the plate pin 5 (through a .05 uf capacitor ) modulated it through pin 7 .back then used a crystal mike and phono cartridge .it was a hot chassis so had to be carefull about inputs . got a half a block with it . . quality is better than commercial a.m. broadcasting (5 khz bandwidth -typical ) not that mine was 20-20 khz but sounded better then.
    that brought back back memories.
    thanks rossgg

    #3333
    phil
    Forum Participant

    how do you connect the stereo output jack of the mp3 player to the unit? Does it combine both sides and broadcast mono? Could you use two AMT300 units to broadcast the two sides separately and play it through two radios both tuned to their own respective frequencies? Would that just sound horrible?
    They do offer the AMT5000 can we assume the main difference between the 3000 and 5000 is in the range and not the audio quality?
    Phil

    #3334
    Ed Stone
    Forum Participant

    The SSTRAN AMT3000 has two jacks on the back so you can plug a stereo cable (eg. 3.5mm jack to two RCA phonos) into the back – it combines them into a mono signal. You could indeed buy two AMT3000 units and transmit a channel on one frequency (on one unit) and another channel on a diiferent frequency on the other and receive on two separate receivers for stereo. No really sure I see the point thought… I undertand the AMT5000 has a better matching arrangement to allow its output to be better coupled to an antenna and therefore increase the range, plus some improvements in the audi circuit. Not worth the extra dough in my opinion.

    #3354
    mukerjea
    Forum Participant

    I have the same AMT 3000 and I just love the quality of sound.

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