YES! You are reading the rules correctly.

There are many 60 meter mobiles running 300 to 400 watts into a 10% efficient
antenna relative to a 1/2 wavelength dipole.

Get on 60, It;s is a great band.

Cecil Moore wrote:
60m operation is limited to 50w pep relative to a
1/2WL dipole. Since a typical 60m mobile antenna
would be much less than 50% efficient, seems it
would it be OK to run an IC-706 at its normal 100
watt output level. Am I reading the rules right?

So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?

Scott
N0EDV

Dave wrote:

YES! You are reading the rules correctly.

There are many 60 meter mobiles running 300 to 400 watts into a 10%
efficient antenna relative to a 1/2 wavelength dipole.

Get on 60, It;s is a great band.

Cecil Moore wrote:

60m operation is limited to 50w pep relative to a
1/2WL dipole. Since a typical 60m mobile antenna
would be much less than 50% efficient, seems it
would it be OK to run an IC-706 at its normal 100
watt output level. Am I reading the rules right?

Scott wrote:
So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?

Radiation resistance/Feedpoint resistance?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in news:rUCDh.2296$re4.1031
@newssvr12.news.prodigy.net:

Scott wrote:
So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?

I am guessing that as an armchair operator, you would use a commercial
antenna.

Given your licence conditions on 60m, it would be very reasonable to ask
your supplier for a written statement (that you can file to fulfil your
licence obligations) of the gain of their antenna in installations like
yours so that you can calculate the maximum input power allowed. If that
is too hard, perhaps a written statement of the permitted maximum input
power for compliance with the licence.

Some of this in tounge in cheek, I just can't see antenna manufacturers
'fessing up to a range of gain figures for typical HF mobile antennas /
installations.

In time, the regulator will wise up to the challenge and specify things
more simply, eg if you use an antenna of less than 8' in length, you can
run up to 100W, otherwise up to 50W. That is more understandable to our
(eg VK) new six hour hams with their shack on their belt.

Owen

But...how does one measure those, or is it done by calculating them and
then applying to the formula below?



Cecil Moore wrote:
Scott wrote:

So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?


Radiation resistance/Feedpoint resistance?

Scott wrote:
But...how does one measure those, or is it done by calculating them and
then applying to the formula below?

EZNEC will give an estimate of the radiation resistance.
Feedpoint resistance can simply be measured.
--
73, Cecil http://www.w5dxp.com

On Feb 23, 7:06 am, Scott wrote:
So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?

Scott
N0EDV



Dave wrote:
YES! You are reading the rules correctly.

There are many 60 meter mobiles running 300 to 400 watts into a 10%
efficient antenna relative to a 1/2 wavelength dipole.

Get on 60, It;s is a great band.

Cecil Moore wrote:

60m operation is limited to 50w pep relative to a
1/2WL dipole. Since a typical 60m mobile antenna
would be much less than 50% efficient, seems it
would it be OK to run an IC-706 at its normal 100
watt output level. Am I reading the rules right?- Hide quoted text -

- Show quoted text -

Hmmm, one could go to Terman, et. al... Lots of heavy math... ughhhh
One could ask the mobile whip manufacturer what the relative gain of
his product is - On second thought that's unlikely to get an answer
other than 42... (See: HitchHikers Guide To the galaxy)

Or one could do the bone simple, farm boy stupid, yet amazingly
effective method of comparing the relative length of the mobile whip
to a quarter wave vertical...
First, the quarter wave vertical is half the length of a dipole so you
immediately have a multiplier of 2...
(Awwww right you nit pickers, DOWN! - Yes I know about vertical-P
loss compared to horizontal-P, but I'm farm boy simple for this one)
Assume the 1/4 Lambda vertical is 45 feet (rough number, I'm a farm
boy, remember) and the whip is 8 feet... Then 45/8 = 5.6 ratio...
So 2 times 5.6 = 11.2 ratio so far...
Therefore 11.2 times 50w = 284 watts...

Now the efficiency of a mobile whip that is just over 20% tall (of a
quarter wave) is roughly 8%-10% (swag) Lets call it 10% for rough
numbers therefore we can expand the 284 watts by dividing 0.1 into
it... or 2840 watts.... Which will make your IC-706 sweat a bit...

OK nitpickers, have fun...

denny / k8do

Scott wrote:

So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?

Scott
N0EDV

SNIPPED

There are two easy methods and one rule of thumb method that will get you into
the ballpark.

1) As Cecil replied, divide the radiation resistance by the feedpoint
resistance. EZNEC will give a reasonable value for radiation resistance and an
MFJ 259B [~$250] will give a measure of the feedpoint resistance.

2) A freeware program, mobile antenna, will also calculate the efficiency.

3) [Rule of thumb] The gain is proportional to the effective aperture in square
wavelengths. So, as mentioned in another reply, approximately, the ratio of
length of the mobile antenna [~8 feet] to the length of a 1/2 wavelength antenna
for 60 meters [~93 feet] yields 8.6% efficiency. So, 100 watts from an IC-706
[series] yields ~9 watts effective radiated power. Conclusion, 50 watts ERP on
60 meters with a 9% efficient antenna would require 555 watts into the antenna.

/s/ DD

Dave wrote in
:

....
3) [Rule of thumb] The gain is proportional to the effective aperture
in square wavelengths. So, as mentioned in another reply,
approximately, the ratio of length of the mobile antenna [~8 feet] to
the length of a 1/2 wavelength antenna for 60 meters [~93 feet] yields
8.6% efficiency. So, 100 watts from an IC-706 [series] yields ~9 watts
effective radiated power. Conclusion, 50 watts ERP on 60 meters with a
9% efficient antenna would require 555 watts into the antenna.
....

It certainly is ROT that in the general case, and in this case, that you
can run a tape measure over an antenna to calculate the aperture area and
in turn calculate gain.

Can you explain how your method deals with capturing the effects of a high
loss loading coil vs a low loss loading coil in such an antenna?

Owen

I'll rely on the calculation from the freeware program "Mobile Antenna". That
program allows variation in coil designs to be specifically input as a variable.

If you have a better answer or method then please provide it.

The original post is basically asking if 100 watts can be run from a 706 in a 60
meter mobile. The answer is YES. Why? Because an eight feet long antenna is
substantially less than the reference dipole. [Typically it is -10dBd].

/s/ DD, W1MCE

Owen Duffy wrote:
Dave wrote in
:

...

3) [Rule of thumb] The gain is proportional to the effective aperture
in square wavelengths. So, as mentioned in another reply,
approximately, the ratio of length of the mobile antenna [~8 feet] to
the length of a 1/2 wavelength antenna for 60 meters [~93 feet] yields
8.6% efficiency. So, 100 watts from an IC-706 [series] yields ~9 watts
effective radiated power. Conclusion, 50 watts ERP on 60 meters with a
9% efficient antenna would require 555 watts into the antenna.

...

It certainly is ROT that in the general case, and in this case, that you
can run a tape measure over an antenna to calculate the aperture area and
in turn calculate gain.

Can you explain how your method deals with capturing the effects of a high
loss loading coil vs a low loss loading coil in such an antenna?

Owen