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Discussion in 'General Technical Questions and Answers' started by W4BD, Oct 15, 2009.

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  1. W4BD

    W4BD Ham Member QRZ Page

    Well I bought a CushCraft A3S a couple of years ago and I am wanting to put it up and use it. The problem is that when the ham took it down he didn't mark any of the traps as to which they were or where they went. I called MFJ/CUSHCRAFT and didn't get much help. I sent an email this morning requesting more help. I have tried to use my Heath GD-1B and I am not having any luck finding the resonant frequency of the traps. I am assuming that the longest traps are for 15M and the shorter are for 10M but I have been known to be WRONG.

    I can't figure out why CUSHCRAFT didn't mark these traps with some type of marking that would last. The book says that they have a arrow on them and I guess CC just stuck a paper tape on and run it on out the door.

    Does anybody out there have a idea of what frequency that the traps will resonate at or an idea of how to ID the traps for sure?

    You can bet on 2 things, The Sun will come up in the morning and if and when I ID these traps they will be engraved with the trap model and the arrow.
  2. W9GB

    W9GB Ham Member QRZ Page

    Bill -

    Although not specific for the Cushcraft AS3, the older AV vertical traps were identical in construction.
    These notes were compiled from conversations with Ed Hammond, formerly of Cushcraft. Traps.htm

    The method of coupling to the dip oscillator is important. Traps from the AV series of antennas require capacity coupling because the coil is shielded. Place a trap on an insulated surface (large cardboard box) and couple your dip oscillator meter (GDO) to the trap as shown below. Be careful to follow directions explicitly.

    For Capacitive Coupling -- the tip of the GDO coil should be just slightly Inserted into the lower end of the aluminium tubing of the trap. Inductive coupling can be used where the coil is visible except for the TV trap where the dip can be found easier by capacity coupling.
    When checking dual frequency traps (TQ & TS) short the trap not under test to prevent obtaining a false reading. It should be noted that the dip meter frequency is lower than the operational frequency of a trap.
    This is caused because the trap will load the dip oscillator and lower it's frequency. You should use the listed oscillator frequencies as a guide. Temperature and humidity can have a +/- 100 kHz effect on traps.
    If the readings are within 100 KHz of the listed amounts, do not worry, the effect upon the assembled antenna will be minimal, Shorted turns or other serious defects will cause wide shifts from the norm.
    One or two megahertz is a definite indication of a bad trap . All coils are sealed and are difficult to repair properly. When all traps are checked and corrected, reinstall them in proper order, (as you previously marked them) and your multiband trapped vertical is now ready for action."
  3. W0GI

    W0GI Ham Member QRZ Page

    Here is the PDF manual if you don't have it.

    Tha good news, is that there are 3 different traps. All six 10 meter traps are the same. For 15 meters there are 4 traps for the driver and reflecter, and 2 traps that are for the director.

    Did you pull the caps to see if there are markings inside?

    At this point, you may be able to identify them by looking inside at the actual turns on the coils, and values of the caps if they have them.

    Sort them as follows:

    The six that are the same will be the 10 meter traps. You will have two that will be the same and they are the 15 meter director traps. The remaining four will be the 15 meter driver and reflector traps. I think you will be in business.

    Now find the engraving tool. :)

    73 - Bob
  4. W4BD

    W4BD Ham Member QRZ Page


    Well I pulled the covers off 3 of the traps 2 short and 1 long. I found a coil with 18 turns in the 2 short traps and a coil with 31 turns in the long trap. I don't know if my GDO has messed up now because I can't seem to find any type of reading on the coils without the cover in place. I will keep playing with it for a while longer.
  5. W0PYZ

    W0PYZ XML Subscriber QRZ Page

    I had the same problem you're having a few months ago when I purchased a disassembled A3S.

    The most obvious way in which the traps differ from each other is in physical shape and size. The traps on the "outboard" end of the elements frequently are swaged (reduced in diameter) on the outside end. This is true of the 15m traps (TB and TC) on the A3S.
    The TA, TB and TC traps use a 12" can (the length of the can does not include the length of the 7/8" or 5/8" OD (if swaged) tubing on the ends.

    For traps that are the same size and shape, we must look for other distinguishing features. For example, the "TB" and "TC" 15m traps are the same size, but the length of 7/8" OD tube exposed on the boom side of the trap (see below on how to determine the boom side of the traps) is shorter for the "TB" by about 1/2". The "TB" has a correspondingly longer swaged end. The same coil is used for both (TB and TC) but the coil on the TB is inserted further inside the can to raise the resonant frequency.

    The correct orientation of the "TA" traps for the A3S can be found by looking under the plastic covers on either end and discovering which end has the can bent-in and fixed to the input tube with a heavy sheet metal screw. The end with the can bent-in goes closest to the boom. You will see the same sheet metal screw on the "TB" and "TC" traps , but they do not have this same ambiquity as to the orientation, since they (TB and TC traps) can only be inserted one way.

    To frequency check the traps, place a trap on an insulated surface (such as a large cardboard box) and couple a dip oscillator to the trap. Make sure to couple it to the end of the trap that goes closest to the boom. Insert the tip of the dip oscillator coil "slightly" into the tubing. When a dip is found pull the oscillator coil out of the end of the trap slightly and re-dip the oscillator. Continue to pull the dip oscillator coil out of the tubing and re-dip until you have the smallest perceptable dip. It should be noted that the dip meter frequency is lower than the operational frequency of the trap. This is caused because the trap will load the dip oscillator and lower its frequency. here is chart for the frequencies:

    Trap Oper freq. Dip Osc freq.
    TA 28.60 27.50
    TB 21.50 20.39
    TC 21.30 20.20

    I hope this information helps you.

    NL7XT likes this.
  6. W4BD

    W4BD Ham Member QRZ Page



    Well this is the info I think I have been looking for. I will put the covers back on the 3 I have off and start from scratch in the morning. I bought this beam from a ham and was told that he had marked the traps but I haven't found it yet.

    I may be able to figure it out now.

    MANY THANKS!!!!!
  7. W0GI

    W0GI Ham Member QRZ Page

    You'll get it figured out Bill. :) It's a good antenna, so worth the effort.

    When I left CA 4 years ago, I gave my A3S to a local kid that was starting out, and just got his tech. I wonder how that went, as we marked them when we took it down?

    I have an R7000 in the garage that will be going up this week. The hole was dug today, and the concrete and mast will go in the yard tomorrow.

    I shrink wrapped that thing four years ago. The tube gets smaller as it goes up, and the traps were left attached, so I hope it won't be a mystery like your situation.
  8. W4BD

    W4BD Ham Member QRZ Page


    Well with the info that W0PYZ posted I may have these traps figured out. The problem in my mind now is the TB & TC all resonate very close to the frequency so it's hard for me to know for sure when I have the "DIP" right. According to the info that W0PYZ posted I only have 6 traps to sort out now instead of 12. I guess now I will put the antenna together and point it straight up and put some rf power to it and see what the VSWR is on the bands.

    I will say this for the pennies that CUSHCRAFT saved by not stamping the ID of the trap will make me think twice about buying CC again. Course CC has been bought by MFJ and so I will have to see if MFJ improves things or just lets things stay the same.
  9. W0GI

    W0GI Ham Member QRZ Page

    Using an SWR reading is only going to be useful for the driven element. You will still not know if you have the correct traps on the reflector and director.
  10. W4BD

    W4BD Ham Member QRZ Page



    Well yes this is true but I only have 6 traps now that are in question vs 12 before. The post that Gene W0YPZ made had some VERY good info about the length of the ends and also the shape (Swagged) so with that info I was able to measure and think that I have them sorted out now. I will confirm the ID of the traps for sure and certain before I get the air scribe and mark them.

    Maybe I will get some information from MFJ/CUSHCRAFT this coming week. From what I was told the CC operation is in process of moving to MS.
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