HR2.0 Episode 146 - BTECH U25D Amp Testing

Discussion in 'Amateur Radio News' started by KC5HWB, Aug 8, 2018.

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  1. KC5HWB

    KC5HWB Ham Member QRZ Page

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  2. N1NDN

    N1NDN Ham Member QRZ Page

    I don't believe that the small cable from the radio to the amp would induce that much attenuation! I believe either the amp doesn't really go in to bypass mode when its shut off or you have a defective cable. Something else to consider is that you're output of 25 watts with the amp on is either very good if its really getting a quarter watt input or not good at all if its getting a full 5 watt input. Further testing with a different SMA cable should be posted, there's too much of a mystery here to consider the amp to be ok or not.
     
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  3. WM3M

    WM3M Ham Member QRZ Page

    I have had this amp for a couple weeks now, the AMP-U25D for DMR, it works, sort of. I use it with an MD-380, at 5 watts into the amp. Using the mic on the U25D, with the connection to the HT there is steady clicking, pulsing, ticking type sound on my signal. It is very noticeable and distorts my DMR signal. I tried everything I could think of, grounding everything, ferrite chokes on all leads, different locations, pulsing still there. When I use it just as an amp, RF into the U25D from the MD-380 only, signal is fine and clear. Measuring wattage on FM, it puts out about 35 watts, do not have a way to measure wattage on DMR. I really wanted to use the U25D with its mic and speaker and not just as an amp, so not sure it is worth it, but its the only amp for DMR I have found. The loss noted in the above video is not from the small cable, if you turn off the amp it does not go into by-pass, it does not pass the RF, so if the amp is off, there is not RF out. Using just as an amp and not with the supplied mic, cables, etc. it does work well on UHF DMR, I can work several more UHF DMR repeaters at quite a distance, using an outside, roof mounted antenna. Emory WM3M 73
     
  4. AA1PR

    AA1PR Ham Member QRZ Page

    adore your videos
    but they are way too long
     
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  5. KG2C

    KG2C XML Subscriber QRZ Page

    I stopped watching when the host said "We can't hear fast enough to hear 33 times a second". I think he would have benefited from reading the Wikipedia article on TDMA before telling people how TDMA works.
     
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  6. KD5RJZ

    KD5RJZ Ham Member QRZ Page

    Review is useless without knowing the insertion loss of the cables.
     
  7. KC5HWB

    KC5HWB Ham Member QRZ Page

    I think you are right about the amp not passing traffic when it is powered off - which is a poor design, imo. But 25-watts out with 5-watts in is pretty standard for an HT amp.
     
  8. KC5HWB

    KC5HWB Ham Member QRZ Page

    Thanks for this info - you are someone who actually used the amp, so your notes are accurate. I think the fact that the amp doesn't pass RF when powered off is a poor design, but I didn't have any of the clicking in my TX that you are describing.
     
  9. KC5HWB

    KC5HWB Ham Member QRZ Page

    Because Wikipedia, written by any schmo with a keyboard, is always accurate, right?
    Also, if you read the article you link, it never contradicts what I said. I can show you articles online that say 33 m/s, 30 m/s or 36 m/s. Perhaps it is a secret that no one actually knows
     
  10. KD6VXI

    KD6VXI Ham Member QRZ Page

    The last real technical review I saw of one of these amplifiers (possibly branded a different name) showed that at 35 watts it couldn't meet itu standards by c 3.5 dB.

    That means if you hook it up to an antenna, you are in violation. That also means as you turn the power up, it gets magnitudes worse.

    As such, use at your own risk. Most of the ChiCom garbage has zero filtering. It's YOUR responsibility to not be as ignorant as a CBer.

    --Shane
    KD6VXI
     
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