Hm.

All in the same sentence, that "line losses are negligible" and "line
losses will be about -3 dB"? I assume, of course that you mean 3 dB, not
-3 dB. But does this mean that you consider 3 dB to be negligible? And
how did you calculate that as the line loss?

Roy Lewallen, W7EL

Dave Shrader wrote:
Assuming a VSWR of 10 to 1, reasonable for 80 meters, and assuming line
losses are negligible for open wire tuned feeders, also reasonable for a
first approximation, your line losses will be about -3 dB.

EZNEC indicates that you will also have a VSWR of about 10:1 on 40 meters.

Conclusion: you will experience about -3 dB loss [1/2 S unit] on both 75
and 40 when fed with 500 ohm line.

Deacon Dave, W1MCE

I should have been more specific. The line loss, in a 500 ohm open wire
tuned feeder system, IF MATCHED, can be assumed to be negligible. The
presence of the additional losses caused by the amplitudes of the
reflected components at a VSWR of 10:1 will be about 3 dB.

Is 3 dB negligible? It's approximately 1/2 S unit. Whether or not 3 dB
is negligible depends on the individual station. I get one judgment if I
consider QRP and a different judgment if I consider QRO. For me, 3 dB on
75/40 is acceptable due to a single antenna limitation and 1 KW output.

Roy, thanks for challenging my 'loose language'.

DD

Roy Lewallen wrote:

Hm.

All in the same sentence, that "line losses are negligible" and "line
losses will be about -3 dB"? I assume, of course that you mean 3 dB, not
-3 dB. But does this mean that you consider 3 dB to be negligible? And
how did you calculate that as the line loss?

Roy Lewallen, W7EL

Dave Shrader wrote:

Assuming a VSWR of 10 to 1, reasonable for 80 meters, and assuming
line losses are negligible for open wire tuned feeders, also
reasonable for a first approximation, your line losses will be about
-3 dB.

EZNEC indicates that you will also have a VSWR of about 10:1 on 40
meters.

Conclusion: you will experience about -3 dB loss [1/2 S unit] on both
75 and 40 when fed with 500 ohm line.

Deacon Dave, W1MCE

Dave Shrader wrote:
I should have been more specific. The line loss, in a 500 ohm open wire
tuned feeder system, IF MATCHED, can be assumed to be negligible. The
presence of the additional losses caused by the amplitudes of the
reflected components at a VSWR of 10:1 will be about 3 dB.

Not with open-wire transmission line on 75m. It would be less than
one dB.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

You've still lost me. If the line loss is negligible when matched, even
a high SWR won't increase loss appreciably. That is, in fact, why people
use open wire line when the SWR is high. So I don't believe your 3 dB
figure is correct. Where did it come from? How was it calculated?

Roy Lewallen, W7EL

Dave Shrader wrote:
I should have been more specific. The line loss, in a 500 ohm open wire
tuned feeder system, IF MATCHED, can be assumed to be negligible. The
presence of the additional losses caused by the amplitudes of the
reflected components at a VSWR of 10:1 will be about 3 dB.

Is 3 dB negligible? It's approximately 1/2 S unit. Whether or not 3 dB
is negligible depends on the individual station. I get one judgment if I
consider QRP and a different judgment if I consider QRO. For me, 3 dB on
75/40 is acceptable due to a single antenna limitation and 1 KW output.

Roy, thanks for challenging my 'loose language'.

Total loss = 10*log((a^2-|rho|^2)/(a(1 - |rho|^2))

ARRL Antenna 18th edition, Chapter 24, Equation 15

Whe a = matched line loss = assumed 1
rho = 0.8181 reflection coefficient for VSWR = 10

+ + +

OOOPPPSSS!!! Math error!

Reviewing my calculations I made a major math error!! Glad I kept the
work sheet.

In the numerator I used rho^2 not (1 - rho^2).

Now I am glad I retired from Engineering. :-)

Thanks again Roy!!

Conclusion, after I failed my ALGEBRA course, sheepish grin, the
additional loss is zero within the stated assumptions. Which just proves
I made 'Much ado about Nothing'.

Deacon Dave, W1MCE

I'll say three Hail Mary's and three Our Father's, assuming I can still
count to three!!

+ + +

Roy Lewallen wrote:

You've still lost me. ... Where did it come from? How was it calculated?

Roy Lewallen, W7EL

Dave Shrader wrote:
Total loss = 10*log((a^2-|rho|^2)/(a(1 - |rho|^2))

ARRL Antenna 18th edition, Chapter 24, Equation 15

Whe a = matched line loss = assumed 1

The reference calls quantity "a" the "matched line loss ratio", and a
value of 1 means no loss.

Does this mean that you are calculating the line loss in a lossless line?

rho = 0.8181 reflection coefficient for VSWR = 10

+ + +

OOOPPPSSS!!! Math error!

Reviewing my calculations I made a major math error!! Glad I kept the
work sheet.

In the numerator I used rho^2 not (1 - rho^2).

Now I am glad I retired from Engineering. :-)

Thanks again Roy!!

Conclusion, after I failed my ALGEBRA course, sheepish grin, the
additional loss is zero within the stated assumptions. Which just proves
I made 'Much ado about Nothing'.

Deacon Dave, W1MCE

I'll say three Hail Mary's and three Our Father's, assuming I can still
count to three!!

+ + +

Roy Lewallen wrote:

You've still lost me. ... Where did it come from? How was it calculated?

Roy Lewallen, W7EL




--
================================================== ======================
Owen Duffy )
Phone: +61 2 6257 3872 (02) 6257 3872
Mobile: +61 417 408 424 0417 408 424
================================================== ======================