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Matching End-fed Halfwave with K2/KAT2?

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Daniel Reynolds-2

Matching End-fed Halfwave with K2/KAT2?

I'm considering using an end-fed halfwave for Field Day, and I have an idea how
I might implement it, but need some technical assistance from those in the
"know".

What I'd like to do is pick up a few toroid cores (one to break, one to lose,
and another to use) to build a simple transformer with a couple turns attached
to a short (2-3 ft) pigtail of coax going back to the K2/KAT2. I'm hoping I can
experimentally determine how many secondary turns to use for the halfwave side
of things. Will the KAT2 be sufficient to handle the 'fine tuning' after I
handle the major impedance transformation through the toroid? or will I need to
get my hands on an air variable to do fine tuning on the antenna end of the
pigtail?

Any ideas on how to best implement this would be greatly appreciated -
especially since I'll need to know which core(s) to buy this week so I can test
this out before Field Day.

If there's a cheaper way to do this using simple plastic pill bottles and air
wound cores - I can do that too ... but I also like to wind toroids ;-)

I'll probably end up with 1 or 2 antennas ... a 40/20/15 (40m halfwave), and
maybe an 80/40/20 (80m halfwave). I may try to orient these crosswise to
provide E-W coverage on 80/40/20 and N-S coverage on 40/20/15 - knowing that
both of these antennas will start producing interesting lobes on the shorter
wavelengths.

Thanks for any help this list generates...

73,
Daniel AA0NI
Oklahoma City
http://www.aa0ni.org

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Don Wilhelm-3

RE: Matching End-fed Halfwave with K2/KAT2?

Daniel,

Although an end fed halfwave antenna is easy to deploy, it presents a very
high impedance at the end. The KAT2 has a difficult time matching a high
impedance load.

Your transformers may work (I can't really comment), but a simple parallel
tuned circuit (wound on a pill bottle and tuned with a capacitor) will
certainly work a lot easier. You can do a 'rough match' with the tuned
circuit (fixed high voltage capacitor) and let the KAT2 refine the matching.
You would need a parallel tuned circuit for each band. The coax attaches to
a link coil wound of a couple turns wound at the 'cold' end of the parallel
tuned circuit - the link has about 5% of the number of turns as the tuned
winding), or can be fed at a tap on the coil. Experiment with your antenna
analyzer.

Another alternative would be to add a quarterwavelength of parallel feedline
to the end of the halfwave radiator - this is the classic Zepp antenna. You
would need an electrical quarter wave cut for each band you will operate.
The quarter wave line transforms the high impedance at the end of the
halfwave down to a low impedance.

Of course, and even easier alternative is to cut the halfwave antenna in
half and feed it with the parallel feedline in the center - in that case it
should work on all bands with a parallel feedline sized to reach from the
antenna to the operating position.

I would believe that a W3EDP antenna - 85 ft. radiator with a 17 ft.
counterpoise wire would be just as easy to deploy as an end-fed dipole and
the KAT2 will handle it on all bands without the bother of the parallel
tuned circuit. You may want to consider that as an alternative.

73,
Don W3FPR

> -----Original Message-----
>
> I'm considering using an end-fed halfwave for Field Day, and I
> have an idea how
> I might implement it, but need some technical assistance from those in the
> "know".
>
> What I'd like to do is pick up a few toroid cores (one to break,
> one to lose,
> and another to use) to build a simple transformer with a couple
> turns attached
> to a short (2-3 ft) pigtail of coax going back to the K2/KAT2.
> I'm hoping I can
> experimentally determine how many secondary turns to use for the
> halfwave side
> of things. Will the KAT2 be sufficient to handle the 'fine tuning' after I
> handle the major impedance transformation through the toroid? or
> will I need to
> get my hands on an air variable to do fine tuning on the antenna
> end of the
> pigtail?
>
> Any ideas on how to best implement this would be greatly appreciated -
> especially since I'll need to know which core(s) to buy this week
> so I can test
> this out before Field Day.
>
>
> If there's a cheaper way to do this using simple plastic pill
> bottles and air
> wound cores - I can do that too ... but I also like to wind toroids ;-)
>
> I'll probably end up with 1 or 2 antennas ... a 40/20/15 (40m
> halfwave), and
> maybe an 80/40/20 (80m halfwave). I may try to orient these crosswise to
> provide E-W coverage on 80/40/20 and N-S coverage on 40/20/15 -
> knowing that
> both of these antennas will start producing interesting lobes on
> the shorter
> wavelengths.
>
> Thanks for any help this list generates...
>
> 73,
> Daniel AA0NI
> Oklahoma City
> http://www.aa0ni.org
>
>

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Andrew Moore-4

Where is K1 C78 located?

I am modifying a Rev D. K1 board to add the C78 capacitor (10 uF) for 80
meter operation. According to instructions, C78 is located on the bottom of
the board near the "PA" and "12V" labels. However I see no reference
designator for C78, either on top of on bottom of the board at this
location.

Where exactly should I install this capacitor?

Thanks,
--Andrew, NV1B

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Daniel Reynolds-2

RE: Matching End-fed Halfwave with K2/KAT2?

In reply to this post by Don Wilhelm-3

Hi Don,

--- Don Wilhelm <[hidden email]> wrote:
>
> I would believe that a W3EDP antenna - 85 ft. radiator with a 17 ft.
> counterpoise wire would be just as easy to deploy as an end-fed dipole and
> the KAT2 will handle it on all bands without the bother of the parallel
> tuned circuit. You may want to consider that as an alternative.

Sometimes I just need someone to gently shake me back to reality... I've used a
W3EDP and it did fine as far as tuning it is concerned.

I wonder if there's a W3EDP style antenna that is 'bigger' for better
performance on 80m (maybe 170 ft) ? I guess this gives me a good reason to play
with EZNEC.

I did seriously consider the 1/4 wave matching stub (J-pole style), but then I
started to wonder if on 80m, I'd have to have 67 ft of 300 ohm twinlead spread
out along the ground ... or could I twist it up in a coil (is either of these
situations a good thing for a matching stub)? It just seemed to put me further
away from the antenna than I was envisioning, and I was hoping to use each
half-wave harmonically (3.5/7/14/21) and I believe the 1/4 wave matching stub
pretty much makes each one a mono-bander ... but - that's not bad - I'll just
have lots of fun making each end-fed halfwave for each band if I choose this
antenna.

... but what did I buy the KAT2 for? This is why the W3EDP is a perfect
combination for the K2/KAT2.

Why end fed? Because I plan on tossing the other end over the top of a tree or
two and I don't want to mess with feedline and branches.

73 and thanks,
Daniel AA0NI
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Bob Davis-4

Re: Where is K1 C78 located?

In reply to this post by Andrew Moore-4

On My K1 it is on the bottom adjacent to the mounting screw for Q6.

73 de Bob, WG7Y
----- Original Message -----
From: "Andrew Moore" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, June 08, 2006 8:01 AM
Subject: [Elecraft] Where is K1 C78 located?

>I am modifying a Rev D. K1 board to add the C78 capacitor (10 uF) for 80
> meter operation. According to instructions, C78 is located on the bottom
> of
> the board near the "PA" and "12V" labels. However I see no reference
> designator for C78, either on top of on bottom of the board at this
> location.
>
> Where exactly should I install this capacitor?
>
> Thanks,
> --Andrew, NV1B
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

Andrew Moore-4

Re: Where is K1 C78 located?

...but to which pads do the leads connect? I know generally where C78 is
located, but nothing I have found in the archives or in the documentation
says where to connect the actual leads.

Message from Bob Davis ([hidden email]) on 6/8/06 10:30 AM:

> On My K1 it is on the bottom adjacent to the mounting screw for Q6.
>
> 73 de Bob, WG7Y
> ----- Original Message -----
> From: "Andrew Moore" <[hidden email]>
> To: <[hidden email]>
> Sent: Thursday, June 08, 2006 8:01 AM
> Subject: [Elecraft] Where is K1 C78 located?
>
>
>> I am modifying a Rev D. K1 board to add the C78 capacitor (10 uF) for 80
>> meter operation. According to instructions, C78 is located on the bottom
>> of
>> the board near the "PA" and "12V" labels. However I see no reference
>> designator for C78, either on top of on bottom of the board at this
>> location.
>>
>> Where exactly should I install this capacitor?
>>
>> Thanks,
>> --Andrew, NV1B
>>
>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft
>>
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>
>
>

Don Wilhelm-3

RE: Where is K1 C78 located?

In situations like this, the schematic comes in quite handy - it indicates
which components are connected to other components. In fact, a schematic
really serves no other purpose if taken in a generalized sense.

After locating the possible component pads that it will connect to on the
schematic, the parts placement guide can help in physically locating the
points to be used.

73,
Don W3FPR

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]]On Behalf Of Andrew Moore
> Sent: Thursday, June 08, 2006 10:45 AM
> To: Bob Davis; [hidden email]
> Subject: Re: [Elecraft] Where is K1 C78 located?
>
>
> ...but to which pads do the leads connect? I know generally where C78 is
> located, but nothing I have found in the archives or in the documentation
> says where to connect the actual leads.
>
>
> Message from Bob Davis ([hidden email]) on 6/8/06 10:30 AM:
>
> > On My K1 it is on the bottom adjacent to the mounting screw for Q6.
> >
> > 73 de Bob, WG7Y
> > ----- Original Message -----
> > From: "Andrew Moore" <[hidden email]>
> > To: <[hidden email]>
> > Sent: Thursday, June 08, 2006 8:01 AM
> > Subject: [Elecraft] Where is K1 C78 located?
> >
> >
> >> I am modifying a Rev D. K1 board to add the C78 capacitor (10
> uF) for 80
> >> meter operation. According to instructions, C78 is located on
> the bottom
> >> of
> >> the board near the "PA" and "12V" labels. However I see no reference
> >> designator for C78, either on top of on bottom of the board at this
> >> location.
> >>
> >> Where exactly should I install this capacitor?
> >>
> >> Thanks,
> >> --Andrew, NV1B
> >>
> >>
> >> _______________________________________________
> >> Elecraft mailing list
> >> Post to: [hidden email]
> >> You must be a subscriber to post to the list.
> >> Subscriber Info (Addr. Change, sub, unsub etc.):
> >> http://mailman.qth.net/mailman/listinfo/elecraft
> >>
> >> Help: http://mailman.qth.net/subscribers.htm
> >> Elecraft web page: http://www.elecraft.com
> >>
> >>
> >
> >
>
>
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Andrew Moore-4

Re: Where is K1 C78 located?

> In situations like this, the schematic comes in quite handy

I hadn't even thought of checking the Rev F. schematic on the elecraft web
site - that did the trick. Thanks.

--Andrew

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