Today's Message Index:
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1. 09:30 AM - Can Antenna problems damage a com transmitter? (user9253)
2. 01:34 PM - Re: Can Antenna problems damage a com transmitter? (Tim Andres)
3. 03:50 PM - Re: Can Antenna problems damage a com transmitter? (Robert L. Nuckolls, III)
Message 1
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| Subject: | Can Antenna problems damage a com transmitter? |
I intend to do some experimenting with homemade com antennas connected to my IC-A200.
Is there a danger of damaging the transmitter if the antenna is either open or
short circuited or otherwise unsuitable?
Thanks,
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=397423#397423
Message 2
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| Subject: | Re: Can Antenna problems damage a com transmitter? |
Hi Joe, yes there is the possibility of damage if not built correctly. I assume
you are building a 1/2 wave dipole or 1/4 wave vertical according to some published
plans and if so, and the elements are cut to the correct length and it
should be ok. Just make sure you have continuity at the radio connector, from
the coax connector center conductor to the individual correct element and from
the connector shield out the the other element. Also ensure you have NO conductivity
between the elements. Then try the receiver, then the transmitter.
The SWR of the antenna can also be influenced by proximity to other stuff, like
you or your airplane. To be safe, buy yourself a SWR meter or borrow one. Then
you will know you are presenting a suitable impedance to the radio.
Good luck
Tim
Sent from my iPad
On Mar 31, 2013, at 9:28 AM, "user9253" <fransew@gmail.com> wrote:
>
> I intend to do some experimenting with homemade com antennas connected to my
IC-A200.
> Is there a danger of damaging the transmitter if the antenna is either open or
short circuited or otherwise unsuitable?
> Thanks,
> Joe
>
> --------
> Joe Gores
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=397423#397423
>
>
>
>
>
>
>
>
>
>
Message 3
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| Subject: | Re: Can Antenna problems damage a com transmitter? |
At 11:28 AM 3/31/2013, you wrote:
>
>I intend to do some experimenting with homemade com antennas
>connected to my IC-A200.
>Is there a danger of damaging the transmitter if the antenna is
>either open or short circuited or otherwise unsuitable?
>Thanks,
>Joe
The very first solid state VHF transmitter I
crossed paths with was indeed vulnerable to
high SWR loading. But that was 1968 and
the transistors were germanium PNP devices.
A lot of improvements have been made over
the years not only in the efficiency of transistors
suited to the task but in their relative ruggedness
as well. Nowadays, it is so easy to build a reflectometer
right into a transceiver. The reflected power
function is used to reduce drive to the transmitter's final
amplifiers such that the transceiver is self protecting in
extreme SWR situations (shorted or open coax).
When using your transceiver for exploratory
measurements, look at SWR first and excited
the test setup for only long enough to see
that your SWR readings are not really out of
whack. The IC-A200 manual allows normal operations
at SWR as high as 3:1 but is silent as to
any cautions for still higher numbers.
Open and shorted coaxes are part and parcel
of living in the real world. Your transceiver
is not at risk for the short duration measurements
you're needing to accomplish.
When ever we needed to make extended tests
on a transmission line/antenna combo with
high SWR, we would stick a 6 db attenuator
in the line (100 feet of RG-58 coax works
good too. The losses through the attenuator/coax
are so great that TERRIBLE swr at the far end has
no great effect on the energy source. The attenuator
would keep the transmitter's auto-power down
circuit happy.
Bob . . .
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