Towertalk
[Top] [All Lists]

[TowerTalk] Cushcraft 40-2CD on 12, 17 & 6m

To: <towertalk@contesting.com>
Subject: [TowerTalk] Cushcraft 40-2CD on 12, 17 & 6m
From: n4kg@juno.com (T A RUSSELL)
Date: Wed, 1 Jul 1998 01:48:12 -0600

On Tue, 30 Jun 1998 22:29:14 -0400 "DavidC" <davidc@bit-net.com> writes:
>
>> The 40-2CD presents a reasonable match on 17M (<2:1 SWR) 
>> and seems to work as an effective  rotary dipole on that band. 
>> The SWR on 12M is higher but can be tuned with most antenna
>> tuners.  I know many people who use this as their primary 17M
>> antenna and a few who also use it on 12M.  It should be possible
>> to add a close spaced 12M parasleeve driven element if you want 
>> to achieve low 12M SWR without a tuner.
>
>What design-type tuner would you recommend for this sort of 
>application? 

        I use a Drake MN-2000 which is a pi-network tuner.
        My friend N4NO made some high band pi-network
        tuners using small variable capacitors and a few
        loose turns of wire (#14?) which works well at 1KW
        on all of the high bands.        de  N4KG 

>L, T, etc? 
>Each has strengths and weaknesses and I am interested in minimal loss 
>and noise.  I am not up to adding a driven element ... yet!  (Is the 
>auto-tuner in my TS-690SAT adequate for this task?)

        It could be.  The exact load impedance will depend on
        the length of coax between the transmitter and antenna.
        Give it a try and see.  If not, build a simple tuner.

        Adding a parasleeve driven element is very simple.
        It is continuous, just like a parasitic element, only 
        spaced closer for tighter coupling, providing dual
        resonance.  Force 12 uses this technique in many
        of their antennas.  The HyGain Explorer is another
        example.     de  N4KG

>> It would be a simple matter to add 12 and 17 meter reflectors
>> (or a trapped reflector a la  A3WS) to achieve 2 effective elements
>> on each band.  The fact that there are no elements in front of the
>> driven element means that there will be NO destructive interference
>> as experienced with 3 or more elements on lower bands.   These 
>> additional elements for the WARC bands will NOT affect 40M
>> operation.  
>
>OK, these would be approximately 18 and 25 foot reflectors inserted 
>between   (actually a little longer...more like 21 and 27 ft or
so..N4KG.)
>the director and 40m reflector?  Hmmm.  Perhaps I can recycle some 
>tubing from the TH6DXX I have laying around.

        Just buy some straight aluminum tubing and put the TH6
        up at 40 ft either as a side mount or on a separate tower.
        (Texas Towers sells aluminum tubing in 6 ft lengths).
        (You're welcome, Gordan.     de  N4KG)
>
>What sort of spacing would you suggest as a starting place?  (I don't 
>have a 40-2CD ... yet ... so I don't have dimensions in hand.) 
Cushcraft 
>is only 25m north of me, perhaps I could beta test these mods for them!
>
        The gain for a 2L reflector type Yagi peaks at 0.15 WL
        (but the peak is very broad so anything from .1 to .2 WL
        will work).   That works out to be 6 ft on 12 M and 8 ft on 
        17M.  If CC will sell you traps for the A3WS, a single
        trapped reflector spaced 7 ft is another possibility.  N4KG

>> I have often thought such an option would make an interesting 
>> product enhancement for Cushcraft.
>
>What do you suppose this does to wind load, balance at the mast, etc?

        The additional wind load is small but it will unbalance 
        the load.   It might be a good idea to double wall the 
        boom at the center with a 6 to 12 ft insert.     de  N4KG
                
>BTW:  Someone mentioned here that the newest version of the 40-2CD 
>(XM240) has a reflector that is isolated from the boom.  What would that

>offer? Should the same be done for these added 12 and 17m reflectors?
>
        The parasitic elements can be either grounded or isolated.

>Thanks! & 73, DavidC  AA1FA
>
>> 73 / GL,  Tom  N4KG
>> .....................................

>> >Over the past week several folks have told me that the 40-2CD tunes
>> >nicely and runs real well on 12 and 17, and that according to an 
>> >MFJ-259 shows a good swr and impedance on 6m (multiple 
>>>wavelengths I guess!).
>> >I would greatly value reports of actual experiences with this 
>antenna 
>> >on these non-design frequencies as I move closer to finalizing my
>antenna plans.
>> >
>> >These are all secondary bands for me and if this beam will handle 
>them I will be able to settle on it as adequate for those bands and 
>return my focus to maximizing 10-15-20.
>> >
>> >This is a wonderful reflector, made so by all herein who love the 
>> >hobby and enjoy the sharing of knowledge and experience!  
>> > Thanks & 73,  DavidC  
>> >AA1FA

_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm


<Prev in Thread] Current Thread [Next in Thread>
  • [TowerTalk] Cushcraft 40-2CD on 12, 17 & 6m, T A RUSSELL <=