Design for matching network for end fed whips?
 

I am wanting to experiment making vertical whips, end fed, for a number of
frequencies
from HF through to UHF and was wondering if someone can point me to a link
with
designs for constructing these.

I want to feed with 50 ohm co-ax for convenience, and I think it basically
has to
resonate at the design frequency, tapped for 50 ohms to feed it and present
a
"high impedance" to the end of the resonant element.

Naturally there will be different designs required for UHF frequencies
compared
to HF frequencies for mechanical considerations and I guess different
matching networks
with different Q's will have pros and cons too..

Anyone with some links / info would be greatly appreciated

Thanks

Nick

Design for matching network for end fed whips?
 

"Nick" wrote in message
...
I am wanting to experiment making vertical whips, end fed, for a number of
frequencies
from HF through to UHF and was wondering if someone can point me to a link
with
designs for constructing these.

I want to feed with 50 ohm co-ax for convenience, and I think it
basically has to
resonate at the design frequency, tapped for 50 ohms to feed it and
present a
"high impedance" to the end of the resonant element.

Naturally there will be different designs required for UHF frequencies
compared
to HF frequencies for mechanical considerations and I guess different
matching networks
with different Q's will have pros and cons too..

Anyone with some links / info would be greatly appreciated

Thanks

Nick


This would all depend a great deal on type of antenna you want to end feed,
1/4, 1/2, 5/8, ect.

Jimmie

Design for matching network for end fed whips?
 

Nick wrote:

[stuff]

Here is a link to get you started:

http://www.aa5tb.com/efha.html

This deals with a 1/2 wave monopole. I have found that 1/2 or 5/8 is
where it is at (antenna radiation pattern), and usually end up
physically shortening the 1/2 wave ant with a loading coil or helically
winding it over the entire shortened length of ant (fiberglass tube,
etc., in the 10 meter band about 8 ft.)

Regards,
JS

Design for matching network for end fed whips?
 

Nick wrote:
I am wanting to experiment making vertical whips, end fed,...

End fed whips? Is there some other way they are fed? In the middle?
At the other end? Am I missing something (and at my age that is likely)?

Irv VE6BP

Design for matching network for end fed whips?
 

"Irv Finkleman" wrote in message
news:BW4ai.6472$xq1.1239@pd7urf1no...
Nick wrote:
I am wanting to experiment making vertical whips, end fed,...

End fed whips? Is there some other way they are fed? In the
middle?
At the other end? Am I missing something (and at my age that is
likely)?

Irv VE6BP

Good points guys...
( I guess a vertical dipole could be fed elsewhere ( centre / 1/3rd
of the way up etc.... )

I elaborate...

End fed half wave dipoles was the original intention, but as JS
remarked, an end fed 5/8ths
seems more interesting.....

One of my applications is for an aerial mounted on a motorcycle
windscreen, fed with
50 ohm co-ax for inter-bike comms... 70 cms (or possibly 2 mtrs)
but needs to be ground plane independent, hence the thought of a
half wave ...

Another is a 16 foot whip for 10 mtrs ....... probably mounted just
under the house gutter

I just want to make myself something for the interest rather than
buy something

Thanks,

Nick

Design for matching network for end fed whips?
 

On 7 jun, 23:50, "Nick" wrote:
I am wanting to experiment making vertical whips, end fed, for a number of
frequencies
from HF through to UHF and was wondering if someone can point me to a link
with
designs for constructing these.

I want to feed with 50 ohm co-ax for convenience, and I think it basically
has to
resonate at the design frequency, tapped for 50 ohms to feed it and present
a
"high impedance" to the end of the resonant element.

Naturally there will be different designs required for UHF frequencies
compared
to HF frequencies for mechanical considerations and I guess different
matching networks
with different Q's will have pros and cons too..

Anyone with some links / info would be greatly appreciated

Thanks

Nick

Hi nick,

When you want to be ground plane independent, a halve wave resonance
is the best option. It does introduce ground currents, but far less
with respect to 1/4 or 5/8 WL. Please note, that you still need some
ground, but a motor cycle frame will be sufficient. When you want to
have full benefit of the HW, you must assure that it resonates as a
half wave (so it will be shorter then an physical half wave). I would
recommend familiarizing yourself with an EM simulation program. It may
save you a lot of experimenting (with negative results).

While the center fed impedance of a HW dipole is not strongly
depending on thickness of radiator, the end fed impedance is. An HF
whip (5m for 10m) will be somewhat below 1 kOhm, however a UHF thick
whip (5mm/70cm band) over a small groundplane will be in the 500 Ohms
range.

The disadvantage of the HW end-fed is his length. When you want to
make it shorter (for example the coil or helix construction), its end-
fed impedance increases significantly. When you halve the length (but
keep halve wave resonance), you may expect a factor 2...4 increase in
impedance.

About matching.
Mechanically, end-fed matching is easiest, you can put the ground to
the motor cycle frame. Elevated feeding gives low feed impedance, but
you also have to include a common mode (balun) function.
For end-feed, you may use an LC section (L in series with coax, C
parallel to antenna), wound transformer, or combination of both.

I assume that you have some means to measure VWSR and or impedance and
don't touch the ends with there is relative high voltage....

Best regards,

Wim
PA3DJS

Design for matching network for end fed whips?
 

"Nick" wrote in message
...

"Irv Finkleman" wrote in message
news:BW4ai.6472$xq1.1239@pd7urf1no...
Nick wrote:
I am wanting to experiment making vertical whips, end fed,...

End fed whips? Is there some other way they are fed? In the middle?
At the other end? Am I missing something (and at my age that is likely)?

Irv VE6BP

Good points guys...
( I guess a vertical dipole could be fed elsewhere ( centre / 1/3rd
of the way up etc.... )

I elaborate...

End fed half wave dipoles was the original intention, but as JS remarked,
an end fed 5/8ths
seems more interesting.....

One of my applications is for an aerial mounted on a motorcycle
windscreen, fed with
50 ohm co-ax for inter-bike comms... 70 cms (or possibly 2 mtrs)
but needs to be ground plane independent, hence the thought of a half wave
...

Another is a 16 foot whip for 10 mtrs ....... probably mounted just under
the house gutter

I just want to make myself something for the interest rather than buy
something

Thanks,

Nick


My trick for feeding a 5/8 is to wind the coil with an 1/8 wl of wire as a
starting point and then trim from there. Using the coil in seies with the
antenna with coax connected between the other end of the coil and the ground
plane(no taps, coil does not conect to ground). This provides a petty decent
match to 50 ohm coax that can be reined a bit by drooping your
counterpoise(radials).

Design for matching network for end fed whips?
 

Thanks for the last two very useful replies...

The desired location for the bike aerial is lower part stuck to the
inside of the screen with as much as high and above the screen as
possible.
The reasons for this are obviously its good to have it as high as
reasonably possible, but also to get it away from the QRM generated
by the electronics around the dash area.

Also, as we ride as a pair, one is always in front or behind the
other, so immediately there is the body mass in the way, screening
the signal. Now this doesn't generally matter as we are usually
withing 200 metres of each other and 1/2 watt at UHF is still full
strength signal, but when we get perhaps a few miles apart and are
in front / behind situation, the body is definitely attenuating the
signal significantly.

Generally one rides in front much of the time, so a rear aerial
gets round this, and a front aerial on the following bike is not
shielded by the riders body - I have both front and rear aerials
and I guess it would be good to have an antenna switch to select,
but BNCs and swopping is no trouble.

The other thing is that everything has to be waterproof where it
matters. I have been experimenting with hot melt glue to pot up
connections - anyone have experience of this as a good potting
agent ? I will put out a separate thread about this as its a bit
hidden in this thread..

Thanks again all - much appreciated

Nick