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

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

Dave wrote:
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].

For a 10' whip, EZNEC says the radiation resistance
on 60m would be ~1.3 ohms. Doubling that for center-
loading yields ~2.6 ohms. Dividing by an estimated
feedpoint resistance of 20 ohms gives an efficiency
of about 13%. Assuming an efficiency of about 90% for
a 1/2WL dipole, I should be able to run
50w*90/13 = 346w. 100 watts should certainly be
justifiable. Heck, I might even fire up my SG-500
at 300 watts. Now the next question. Is anyone using
60m?
--
73, Cecil http://www.w5dxp.com

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?

OK, I take that answer...now, why did the FCC go with an ERP as that
would require calculation rather than a measurement. Hard to measure
ERP as far as I know...

Oh well, go figure!

Scott
N0EDV

Dave 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?

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

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

Cecil Moore wrote:
Dave wrote:

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].


For a 10' whip, EZNEC says the radiation resistance
on 60m would be ~1.3 ohms. Doubling that for center-
loading yields ~2.6 ohms. Dividing by an estimated
feedpoint resistance of 20 ohms gives an efficiency
of about 13%. Assuming an efficiency of about 90% for
a 1/2WL dipole, I should be able to run
50w*90/13 = 346w. 100 watts should certainly be
justifiable. Heck, I might even fire up my SG-500
at 300 watts. Now the next question. Is anyone using
60m?


YEP!!! Quite active here in NE and along the East of the Mississippi River. It
is 1700Z and I'm listening to QSOs on 60-4 and 60-5 from SC and TN. BTW, I'm in NH.

On Feb 23, 7:57 pm, Scott wrote:
OK, I take that answer...now, why did the FCC go with an ERP as that
would require calculation rather than a measurement. Hard to measure
ERP as far as I know...


Because ERP (or EIRP, depending on the application) is how most
licensing works, because that's what's important for spectrum
management in a shared band. Ham radio is somewhat unique in that the
rules are applied on power somewhere in the middle of the system (i.e.
in the feedline from Tx to antenna), with no limits (except for RF
safety) on the radiated field strength. If you can build a 60dBi
antenna and radiate 1.5 GW EIRP, you can do it. (part of that
'encouraging experimentation and advances in the radio art').

yes, commercial broadcast is regulated in terms of power output, but,
since you have to do a "proof of performance" and demonstrate that you
have a certain field strength at a distance, it's really regulating
ERP. Change your antenna gain, and they can conceivably make you
change your Tx power.

On Sat, 24 Feb 2007 03:57:24 +0000, Scott
wrote:

OK, I take that answer...now, why did the FCC go with an ERP as that
would require calculation rather than a measurement. Hard to measure
ERP as far as I know...

Hi Scott,

This never intimidated the FCC when they handed me tests for
RadioTelephone Second and First Class. In this group, we can account
for ERP by using modeling tools such as EZNEC. This and other
modeling tools generally agree with measurements found in the field.

73's
Richard Clark, KB7QHC