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Rebuilding a KLM 2M-14C antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W9GB, Aug 14, 2019.

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  1. W9GB

    W9GB Ham Member QRZ Page

    Six weeks ago, a 30+ year old KLM antenna (2M-14C) arrived at the Antenna Garage : FREE
    After 30 years this classic 2 meter satellite antenna was taken down by a long-time VHF/UHF radio amateur, who is retiring and moving.

    The Phasing Coupling, CS-14C Harness will require a complete reconstruction (and weatherproof protection).
    The SO-239 single hole “D” connector within a PVC cylinder (about size of old 35mm film canister) feeds two (2) coaxial cables (75 ohm, RG-302/U) to the feedpoint of horizontal and vertical folded dipoles.

    A printed circuit board (2.5” x 2.5”), performs the polarization switching (RHP, LHP).
    That board is placed on the horizontal folded dipole (rear driven element).
    The bare PC board and relay were “open to the outdoor elements”.
    The board has been cleaned up with white vinegar.
    There was a 1000 pF capacitor, a diode, and an RCA jack (DC power) on that switch board.

    KLM used a 12 VDC Guardian 1365 relay, 1365PC-2C-12D.
    A New relay is shown below the 30 year old veteran.
    CCACEA91-FDF3-41E3-BC50-08C4C5027B5B.jpeg FBC7B469-0FD6-4EDB-B74B-29C7667F6323.jpeg B4246A7A-F2F9-4B34-A9DD-5DAC44FD305D.jpeg

    The 4:1 coaxial baluns (50 ohm, RG-142/U), placed at feedpoint of the folded dipole driven elements, appear to be OKAY. Shown here below the switching board.
    Everyone needs a project, before the Snow Flies.

    Attached Files:

    Last edited: Aug 14, 2019
  2. W9GB

    W9GB Ham Member QRZ Page

    Matt, KC7EQO had questions about the KLM CS-2 (70 cm) and CS-3 (2m) Polarity Switches used on the KLM satellite antennas (circa 1980). KLM 2M-16C was for 2 meters.

    The KLM CS-2 Manual can be found on page 10 of KLM 435-18CM (70cm antenna)

    NOTE: KLM used the Guardian Relay model # 1365
    RF Parts

    You can Hard Wire the Circular Polarization desired (no switching).
    1/4-wavelength sections of RG-302/U PTFE 75 ohm coax.

    Surplus RG-302/U (MIL-SPEC) sells for $1/foot at Elliott Electronic Supply (Tucson, AZ)
    PTFE coax (RG-302/U) normally has a Velocity Factor of ~ 0.69

    The RG-302/U coax routed to the vertical element is crimped & soldered to #8 Ring Terminals for 16-14 AWG. For default RHCP, center conductor goes to vertical element above mast.
    McMaster Carr part number #7113K38 (sold in pkg. 100)
    There are two (2) 4:1 balun are constructed with RG-142/U PTFE 50 ohm coax.
    Coax length is 1/4-wavelength. Folded dipole on a yagi antenna ~200 ohm at feedpoint.
    #8 Ring terminals are crimped and soldered to coax center conductors, and shields attached together with thin copper strip (with hole for attachment).
    This is connected to the #8 machine screw between feedpoint (bolt thru mast - ground).
    See Pictorial in KLM 144-16C Manual.
    Last edited: Sep 10, 2019
  3. VA7UO

    VA7UO Ham Member QRZ Page

    In the words of Jackie Gleason, "Uff"!
    I haven't seen that relay system for over 35 years, nice. Let us know how the build comes out and by the way, change the baluns. Building new ones will save you grief, you don't know what is inside that cable.

    Glenn, VA7UO
  4. W9GB

    W9GB Ham Member QRZ Page

    Glenn -
    Yes, that is planned. The original 4:1 baluns (photo below)
    built from RG-142/U PTFE coax have been outdoors for 30+ years.
    Assembled RG-142/U (50-ohm) PTFE coax, Brass strip 1.2” x 0.032” (12.7mm x 0.8mm),
    and #8 Ring terminals to DIY build.
    Acquired Formufit 3/4” and 1” PVC (Schedule 40 and Thin-wall) to DIY Build the
    Coax Connector case for the two (2) RG-302/U (75 ohm) feed-lines.
    I may build two (2) versions. One for usage without relay PCB (dedicated Circular Polarization).
    The other an update of the original KLM relay system.

    The tough piece is a weatherproof enclosure for the polarization relay system.
    Bud Industries PNR-2600-C (3.94” x 3.94”)
    UV Tolerant, Gray.

    Last edited: Sep 11, 2019
    VA7UO likes this.
  5. KC4THS

    KC4THS Premium Subscriber QRZ Page

    The original baluns are RG-303, its the same VF and easy to form. you will need 2 @27.50" long. I have made several of them over the years.
  6. NR9Q

    NR9Q XML Subscriber QRZ Page

    I see that the KLM 2m-22c manual calls for RG 142 baluns and the KLM 435-40cx calls RS 303 coax baluns. I looked at the specs for both coax types and they are very similar. Pretty much the same. RG 303 is about .5db better on loss at 440Mhz (this is at 100ft though). Seems like either one would work fine. Is their anything I am missing? This is of concern to me as I am working on rebuild both of these antennas. May not put the switching back on them though (still undecided).

    Also Steve, why 27.5"? I assume I will have more reading to do on this. On the 2m antenna a 1/4 wave would be around 20". Is this because the velocity factor of the Rg 303 is .695? I assume it is, but I would have to look it up. Wish I had my antenna book with me also. NR9Q
  7. W9GB

    W9GB Ham Member QRZ Page

    RG-303 is a 50 ohm coaxial cable.
    My KLM 2M-16C uses RG-3o2/U (75 ohm), stamped on outer jacket.

    KLM 2M-14C and 2M-16C (not longer mfg.) uses a Folded Dipole driven element.
    The coax is required for 4:1 balun construction AND the switching harness.
    Mike Stahl changed the driven element and switching with his newer M2.
    M2 no longer supports the earlier KLM satellite designs. 2M-14C.pdf

    KLM made changes to antenna’s through years (1970s-1980s) based on new materials.
    Pricing of PTFE dielectric coax cable was factor (PTFE shortage in 1980s & early 1990s — due to demand of LAN and fiber-optic cabling. I was purchasing for infrastructure installations in that timeframe).

    Just double check the Velocity Factor (watch impedance, attenuation and price per foot).

    The price of surplus RG-302/U (75 ohm) from Elliott Supply (Tucson, Arizona) is now $3.95 / foot
    That is a significant price increase, from the $1.00/foot last year !

    Elliott also sells RG-303/U (50 ohm) coaxial cables $3.80 / foot.
    Last edited: May 3, 2020
  8. KC4THS

    KC4THS Premium Subscriber QRZ Page

    I have several 2m KLM CP antennas. 2m-14c, (circa 1989) 2m-22c, (circa 1995) both antennas have RG-142b and RG-303. The 4:1 balun’s rated @2kw PEP Use RG-303. The CS-3 switch is rated at 600 watts, due to the guardian 1365 relay. The switch uses RG-142b. This assembly make up the unbalance feed point and phasing/ matching system. Note there are two different length’s RG-142b cables for phasing the left and right polarization. Note the CS-3 switch de-rates max power to 600 watts.

    Balun (the bend radius)

    Important things to know.

    1. Remember the Balun is a matching transformer. Here is a great online tool

    2. “Lesson learned” KLM chose RG-303 for the 4:1 balun’s. Rated at 2 kw PEP and RG-142b for the phasing. Why would they do such a thing? The larger RG-142b was to stiff too accommodate the bend radius requirements for mounting to the driven element.

    3. The CS-3 assembly adds about 2.5 dB loss to your link budget. I allowed for this loss and compensated by using 135’ Andrews LDF5-50A 7/8 Heliax.
    73 DE KC4THS
    Last edited: May 5, 2020
  9. KC4THS

    KC4THS Premium Subscriber QRZ Page

    VF for RG-303 and 142b is 0.695 4:1 balun is 1/2 wave for 144 MHz that's 0.72 meter or 27.5590551 inches.

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