Field Strength Meter

Discussion in 'Homebrew and Kit Projects' started by KF4SCI, Jul 9, 2017.

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  1. KF4SCI

    KF4SCI Ham Member QRZ Page

    Decades ago I built a simple field strength meter and since I can't find it the time has come to upgrade.
    Does anyone have a design they want to share?
     
  2. KE0EFX

    KE0EFX Ham Member QRZ Page

  3. KF4SCI

    KF4SCI Ham Member QRZ Page

  4. K9STH

    K9STH Ham Member QRZ Page

    Using a germanium or Schottky diode will make the Heil field strength meter even more sensitive.

    Actually, the circuit is the same as the old Heath field strength meters.

    field strength-1.JPG

    The original, "very rare" plastic meter PM-1 "mirror front" field strength meter is on the left and the "rare" PM-2 is on the right. The "very rare" and "rare" are per Penson's Heathkit book.

    Glen, K9STH
     
  5. KF4SCI

    KF4SCI Ham Member QRZ Page

    The one I built worked great but it was an old design then. I thought that by now there was something even better.
    Try not to laugh but I looked inside my free Harbor Freight cheapo DVM and there is plenty of room to stuff one inside making use of the existing display. A BNC connector for the antenna and a tiny on/off switch & pot could be added to the top. The dvm would still function as intended but with the added feature of a field strength meter.
    If I do it, I'll post pics & the results on how it works.
     
  6. K9STH

    K9STH Ham Member QRZ Page

    I don't know if there would be enough voltage to read on one of the "little red" DMM units from Harbor Freight.

    One of the much more expensive "green" housing Harbor Freight DMM units would probably work. Those do have the ability to read millivolts.

    As for the circuit: When something works very well, often trying to improve the circuit only results in failure! Frankly, there is an old southern proverb: "If it ain't broke, don't try to fix it"!

    Glen, K9STH
     
    KF4SCI likes this.
  7. KG5QBI

    KG5QBI Subscriber QRZ Page

    Also paralleled by:

    If you haven't improved it until it broke, there is still room for improvement.
     
    KF4SCI likes this.
  8. KZ4AK

    KZ4AK XML Subscriber QRZ Page

    I built mine using an AD8307. Works great! For details go to my web site (www.albe24.com), then down to the Homebrew section, then scroll down through the homebrew stuff. ...Or go straight there with: http://www.albe24.com/fsm.pdf
    Scroll down beyond the power meter stuff for the field strength meter.
     
    WA7PRC likes this.
  9. G3YRO

    G3YRO Ham Member QRZ Page

    I always just used a Microammeter and a germanium diode . . . nothing else !

    Roger G3YRO
     
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    The AD8307 (datasheet) is a wonderful part, allowing actual RF power measurement down into the low mW range (at well into UHF range). MANY people have been using it.

    However, there's an error in your "A Sensitive Field Strength Meter for Fox Hunting" article.
    You state:

    "FYI: zero dBm is one milliwatt into a 50 ohm load. For example, -10 dBm would be
    10 dB down from one milliwatt - or - 0.001 milliwatts."

    -10 dBm is 1/10 of 1 mW, or 0.1mW (100 μW).
     

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