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Archer 21-901, 1/4-wave GP base

Discussion in 'CB Antennas' started by Doug_007, Apr 17, 2017.

  1. Doug_007

    Doug_007 New Member

    Apr 17, 2017
    Likes Received:
    Hi all,

    I am wanting to build the old radio shack (Archer 21-901) 1/4 wave CB ground plane antenna.

    As these were mass produced, aiming for exact measurements, allowing for minor construction errors should yield matching (near factory) results.

    There is a link where it is almost completely described in detail by Stephen Dubin & others :


    but I do not know the diameter of the hair pin wire.
    I am referring to it as beta match, forgive me if it is something else.

    I have read:
    All radiators are 104":
    1/2" x 59", 3/8" x 44" , 1/8" wall
    59+44 = 103"
    (but they must overlap as they fit within each other)
    (knowing the un-assembled lengths would be great)

    I have read elsewhere the ground plane radiators should be 5% shorter, but not sure if thats true, or applicable due to the beta match.
    104" x .05 = 5.2"
    98.8" shorter, or 109.2" longer

    Driven element has single drain hole
    Driven element does not contain re-enforcing dowel
    Driven element ?-inches above mounting baseplate due to mounting stud.

    The beta match is 7.5" x 1.5" separation.
    Attaches to underside of ground plane radial, and side of driven element
    Hole for beta match attaches (?-inches) above base plate to driven element.
    (7.5 - (1/2 /2) - 1/8) = 7-1/8" visual estimate
    (beta meas.) - (1/2reflectDiam). - (mountPlate) =

    ?-inches of 1/2" material secured to base plate as radiator, 1"-???
    Ground plane elements offset ?-inches tangent from centre of base : 1-1/4 to 1-1/2 ??? (guess)

    I know if I bend radiators, I can forgo the beta match but modifying the original design is not where I am hoping this thread will go.

    There was one on ebay I missed out on, and have not seen since or I would buy and share it in detail.

    If anyone is willing to measure/confirm the fine details of this antenna, (or have ANY parts of a dead one they'd be willing to part with for examination purposes, please contact me). Or a whole unmodified unit.

    Why not build a different one ?
    I don't need a different one as I have a .64 wave.
    (sorry, not for sale)
    This is somewhat sentimental project as this was my first antenna as a kid.
    I'm pretty sure I have the original manual from 1977.

    Any help would be very much appreciated.


  2. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

    Oct 23, 2005
    Likes Received:
    Doug welcome to the forum.

    I'm on another project right now, but I may be close to a point where I'll have to wait for additional information. If it turns out I am waiting...I will try and fined my only model and apply some of the new information you posted above.

    I don't think I ever got that model to work right. I'm not even sure it is the same model you note above, but I did read the thread from start to finish...to help remind me and it is of modeling interest to me.

    Give me a day or two, OK?
  3. Doug_007

    Doug_007 New Member

    Apr 17, 2017
    Likes Received:
    Thank you :)

    My collected info is from linked post, and one other post found through google. Some measurements are estimates based on posted photos.

    My math for the height of the hole for beta (always thought it was gamma-match) is I think 1/4" in error.

    Archer 3-element "All-Band Monitor Antenna" 20-014 (of which I have one) appears to use a similar base.
    (radials are for 3/8", not 1/2")
    Part# 10-4153-1 & 10-4645-1

    The main element (#5-0325-2) also uses the plastic standoff, so possibly measurements could be stolen from this too.

    I have the manual for that too, part list is quite descriptive.
    For example:
    Ground plane:
    Tube, 7/16"OD x 58" long
    Tube, 3/8"OD x 21.62" long
    Perhaps others could check their manual, while I hunt for mine.

    Were these good antennas worth copying ???
    VHF-lo, VHF-hi, VHF-air, UHF-lo, UHF-hi, monitoring.
    Not sure if anyone tried transmitting from one of these.
    Total height 70", 13' GP diameter.

    Yup, busy for a bit too.
    Will be in NM for 1st week only of may, if anyone has parts they will part with, this is THE time to send them.

    I'm hoping since it's summer, someone will measure the parts when they're up there cleaning the corrosion off the antenna, or have left over peices from one that blew down.
    Can't remember what happened to my old one.
  4. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

    May 15, 2010
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  5. Doug_007

    Doug_007 New Member

    Apr 17, 2017
    Likes Received:
    108" / 1.05 = 102.9" (5%)
    2/3" difference (103.5")

    I had mentioned hearing there was a 5% difference between radiator and ground plane and I guess it makes sense for the ground plane to be larger, and that seems to about fit.
    4.35% fits your numbers.

    If I can find an alumn top/bottom base clamp "set", i'd like to try casting it.

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