Non Resonant Dipoles in Parallel
 

What danger, if any, is there when resonant 40m, 30m, and 20m dipole
elements in parallel with RG58 coaxial cable feed and the radio's
internal ATU are used on the 17m, 15m, 12m, and 10m bands?


The ATU permits loading of the non-resonant bands to full RF output,
but I have had a blown capacitor that is used within the LowPassFilter
for the 40m channel and another capacitor blown within the 12m/10m
channel.


73, de ~ Vince ~

Vince wrote:
What danger, if any, is there when resonant 40m, 30m, and 20m dipole
elements in parallel with RG58 coaxial cable feed and the radio's
internal ATU are used on the 17m, 15m, 12m, and 10m bands?


The ATU permits loading of the non-resonant bands to full RF output,
but I have had a blown capacitor that is used within the LowPassFilter
for the 40m channel and another capacitor blown within the 12m/10m
channel.


73, de ~ Vince ~

Hi Vince, do you know if the caps in the filters blew while the ATU
was in the process of "tuning"? Or did they blow during normal
operation after the ATU had already "tuned"? The filters should see
their designed for impedance after the ATU successfully "tunes" to your
antenna system impedance. The filters will see all sorts of impedances
during the tunning process, and this time the caps in the filters will
be under the most stress. Another could be a connection problem in
your antenna system causing the impedance the ATU sees to change
intermittently.
My xcvr instruction book says use the lowest possible rf output power
setting when using the internal automatic antenna tuner.
Gary N4AST

Vince wrote:
What danger, if any, is there when resonant 40m, 30m, and 20m dipole
elements in parallel with RG58 coaxial cable feed and the radio's
internal ATU are used on the 17m, 15m, 12m, and 10m bands?

The ATU permits loading of the non-resonant bands to full RF output,
but I have had a blown capacitor that is used within the LowPassFilter
for the 40m channel and another capacitor blown within the 12m/10m
channel.

The sum of the forward voltage and reflected voltage probably
exceeded the ratings of the caps. There is a specified limit
to the SWR that can be tolerated on my IC-756PRO, for instance.
Have you measured your SWR on every band and abided by the
maximum SWR specifications for your rig? If not, please do so.
--
73, Cecil, http://www.qsl.net/w5dxp

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On 26 May 2005 07:09:12 -0700, wrote:



Vince wrote:
What danger, if any, is there when resonant 40m, 30m, and 20m dipole
elements in parallel with RG58 coaxial cable feed and the radio's
internal ATU are used on the 17m, 15m, 12m, and 10m bands?


The ATU permits loading of the non-resonant bands to full RF output,
but I have had a blown capacitor that is used within the LowPassFilter
for the 40m channel and another capacitor blown within the 12m/10m
channel.


73, de ~ Vince ~

Hi Vince, do you know if the caps in the filters blew while the ATU
was in the process of "tuning"? Or did they blow during normal
operation after the ATU had already "tuned"? The filters should see
their designed for impedance after the ATU successfully "tunes" to your
antenna system impedance. The filters will see all sorts of impedances
during the tunning process, and this time the caps in the filters will
be under the most stress. Another could be a connection problem in
your antenna system causing the impedance the ATU sees to change
intermittently.
My xcvr instruction book says use the lowest possible rf output power
setting when using the internal automatic antenna tuner.
Gary N4AST

Hi Gary:

I normally leave the ATU in my FT1kD enabled at all times.
In both instances, the ATU had finished tuning for the aerial wires.
Operation on the 40m band actually does not require the ATU to be
enabled, since the VSWR is very good across the lower 100 kHz of the
band.

All caps within the LPF band/channel were replaced at the same time; I
do not know which cap blew out or was the cause of no RF output at the
time on that band. The last time that this happened, (12m/10m LPF) I
did notice that a capacitor closest to the PA finals showed indication
of swetting.

73, de ~ Vince ~
WA2RSX
Stuck on IOTA NA-026

Vince, as far as answering your orginal question, does your antenna
configuration cause caps to fail in the filters in your xcvr, the
answer should be no. If the tuner can achieve a match, or the antenna
system presents a good match, as you indicate it does on 40M, then
everything should be fine.
The filters are between the PA and the tuner. If the tuner does its
job, then the filters and its components should be happy. As I
mentioned, during the tuning process, the filters may get stressed.
Gary N4AST

Double component ratings (4X if possible), if that doesn't work, grab a big
hammer... you'll know what to do... grin

Warmest regards,
John

"Cecil Moore" wrote in message
...
Vince wrote:
What danger, if any, is there when resonant 40m, 30m, and 20m dipole
elements in parallel with RG58 coaxial cable feed and the radio's
internal ATU are used on the 17m, 15m, 12m, and 10m bands?

The ATU permits loading of the non-resonant bands to full RF output,
but I have had a blown capacitor that is used within the LowPassFilter
for the 40m channel and another capacitor blown within the 12m/10m
channel.

The sum of the forward voltage and reflected voltage probably
exceeded the ratings of the caps. There is a specified limit
to the SWR that can be tolerated on my IC-756PRO, for instance.
Have you measured your SWR on every band and abided by the
maximum SWR specifications for your rig? If not, please do so.
--
73, Cecil, http://www.qsl.net/w5dxp

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John Smith wrote:
Double component ratings (4X if possible), if that doesn't work, grab a big
hammer... you'll know what to do... grin

Yep, that's what I did to my last @#$$%&%%$# computer.
--
73, Cecil http://www.qsl.net/w5dxp

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ROFLOL!!! I can just picture you, standing next to your scoot, in the
garage, sledge hammer in hand, and computer bits littering the floor...
great mental visual Cecil!!! grin

Warmest regards,
John

"Cecil Moore" wrote in message
...
John Smith wrote:
Double component ratings (4X if possible), if that doesn't work, grab a
big hammer... you'll know what to do... grin

Yep, that's what I did to my last @#$$%&%%$# computer.
--
73, Cecil http://www.qsl.net/w5dxp

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You are seeing the results of using the ATU for
a purpose it was not designed for. Internal ATU's
in general, were never intended to be used as full
range tuners. They were intended to be used as
"line flatteners", where the mismatch is not too far
out of line...I would use a stouter outboard tuner to
do what you are doing...It's doesn't have to be fancy.
A simple L tuner would probably match most of what
you are doing...BTW...On the bands with very high
SWR, your loss using that rg-58 is going to be
substantial. How bad, depends on the SWR. If you
are under 5:1 or so, not too awful bad...Over 10:1,
it's starting to be loss oclock.. MK