Cecil Moore wrote:


Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?


Ok, I need teaching here. Why would the loss change? The loss on the
line is forced to what happens at the nominal 50 ohms doesn't it? The
SWR shouldn't be able to change it unless the voltage limits are hit I
would think. I need an explanation of why it wouldn't be so.

Thanks.

tom
K0TAR

Tom Ring wrote:

Cecil Moore wrote:
Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?

Ok, I need teaching here. Why would the loss change? The loss on the
line is forced to what happens at the nominal 50 ohms doesn't it? The
SWR shouldn't be able to change it unless the voltage limits are hit I
would think. I need an explanation of why it wouldn't be so.

The loss specified on transmission line charts are usually matched-line
losses (SWR=1:1). When the SWR is higher than 1:1, additional losses
appear due to the higher SWR. There's a chart in my ARRL Handbook that
gives those additional losses. The matched-line loss for 50 ft. of LMR-400
at 3.5 MHz is about 0.1 dB. Wes calculated the total loss at 0.4 dB but I
think that must have been for 100 ft. of LMR-400 at 3.5 MHz with an
SWR of 6.25:1.

The higher SWR causes additional losses because the maximum current and
maximum voltage is higher for the same power delivered to the load than
for the matched-line case.
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

Tom Ring wrote:

Cecil Moore wrote:
Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?

Ok, I need teaching here. Why would the loss change? The loss on the
line is forced to what happens at the nominal 50 ohms doesn't it? The
SWR shouldn't be able to change it unless the voltage limits are hit I
would think. I need an explanation of why it wouldn't be so.

For the same amount of power delivered to the load, transmission
line losses increase with increasing SWR. For a Z0-matched system:
(PLoad = Pfor - Pref) As the load mismatch is increased, energy
reflected from the mismatched load increases and is re-reflected
back toward the load at the tuner Z0-match point. As the load
mismatch is increased, more energy is stored in the transmission
line during steady-state. This is indirect proof that reflected
energy waves actually exist.
--
73, Cecil http://www.qsl.net/w5dxp

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----