Automatic Antenna Tuner,ATU-100 EXT 1.8-55MHz 100W Shortwave

Discussion in 'General Technical Questions and Answers' started by N4SFQ, Nov 25, 2021.

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  1. N4SFQ

    N4SFQ Ham Member QRZ Page

    This antenna tuner (Automatic Antenna Tuner,ATU-100 EXT 1.8-55MHz 100W Shortwave Mini Automatic Antenna Tuner ).
    Question would automatic antenna tuner can work on receiver only to adjust antenna to get good receiving signal or is automatic antenna tuner is for adjusting transmitter only.
  2. VE3WI

    VE3WI Premium Subscriber QRZ Page

    The tuner, like all autotuners, needs a bit of RF applied so it can measure forward & reflected power & decide what combination of capacitors & inductors minimize the reflected when switched in. I have an ATU-100 board that I'm mounting in an enclosure. I attached the user manual. It says the unit needs at least 5 watts. Once it has done its thing, your antenna system will also be optimized for receive on that frequency.
    Dave, VE3WI

    Attached Files:

    SWL37632 likes this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    For receiving only, you need a manual tuner with knobs.
    K8XG likes this.
  4. N4SFQ

    N4SFQ Ham Member QRZ Page

    Dave, VE3WI
    Since i have a radio shack receiver DX394 receiver with rf amplifier built in the receiver does that i can use a automatic antenna tuner?
    El n4sfq
  5. N4SFQ

    N4SFQ Ham Member QRZ Page

    i have radio shack dx394 receiver ,so are you saying cannot use automatic antenna tuner?
    el n4sfq
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    No. You can only use a manual tuner!
    WD5GWY likes this.
  7. VE3WI

    VE3WI Premium Subscriber QRZ Page

    If you can put up a random length wire antenna outdoors, you will probably be OK for general SWLing.

    If you find you do need a tuner, MFJ sells several receive-only tuners & preselectors ( Also there are numerous vendors of QRP antenna tuners that might do the job (e.g., If you're into homebrewing, you can find designs to build a QRP antenna tuner on DXZone (

    Another possibility if you are "space-challenged" is an active antenna, basically a small whip with a wideband preamplifier. MFJ sells those too (they sell just about everything!) Another vendor I know of is MiniKits in Australia ( They are a long distance away but I've dealt with them & they are good folks.

    Hope you find something that works for you.
    Dave, VE3WI
    WB5THT likes this.
  8. NG1H

    NG1H XML Subscriber QRZ Page

    I am reading the original post as two questions:

    1) Can it work? - Well, kind of. As mentioned above normally you would use a transmitter to make it work automatically. But if you read the instruction manual posted above, the top of the eighth page describes the process to manually tune it when in Simple Test Mode. You will want to make a lookup table for the best settings for different frequencies.

    2) Would it help with receiving signals? - Usually yes.
  9. K7TRF

    K7TRF Premium Subscriber QRZ Page

    As others posted above, you cannot easily use an automatic antenna tuner without a transmitter to give the tuner a signal to tune. Yes, as someone pointed out many auto tuners allow you to manually adjust L and C values to achieve a match but that's paying for the complexity of an auto tuner to just use it as a manual tuner. It's far easier and more cost effective to just find a low power manual tuner with knobs and an inductor switch and tune it by hand for loudest signals or loudest band noise.

    I'd look for a new or used manual antenna tuner built for QRP use as you don't need high power handling capability in a receive only application. If you might enjoy building a kit this would work: But if kit building isn't your thing then something like an MFJ-9201 or any of a number of low to medium power tuners on the used market would work just fine.

    Using them is pretty simple, for each operating band turn adjust the inductor switch setting and the two variable capacitors till you hear the loudest signals and or loudest band noise. It can take a while to figure out which inductor setting is best for each band for a given antenna but just keep a cheat card where you note the best inductor switch setting or even settings for all three controls for each frequency range you like to listen to and then you can quickly get back to a good tuner adjustment when you switch bands.

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