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
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