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Coax loss

KD2GOE

KD2GOE

W9WDX Amateur Radio Club Member
May 30, 2013
952
220
173
43
Buffalo
Well I did a power test on 446mhz on 50'..
Testing at the radio I got 23watts
Testing at the other end I get 13w
I am loosing 10w through coax loss....
Is this excessive or something normal?

This is the coax
http://www.davisrf.com/buryflex.php
 
Last edited:

GOE,

23 Watts = +43.6173 dBm
Connector Loss = -0.1 dB
50 ft BuryFlex = -1.4 dB
Connector Loss = -0.1 dB

Total Gain = 43.6173 dBm
Total Loss = -1.6 dB

ERP = 43.6173 – 1.6 = 42.0173 dBm
= 15.9121 Watts

13 Watts / 15.9121 Watts = 0.816988
100 x .816988 = 81.6988 %
100% – 81.6988% = 18.3012% (~18.3%)

You're measuring 13 Watts which is about a 18.3% higher loss than what should be.
Either your transmission line assembly has more loss than expected, or there is
a 18.3% error introduced by the meter, or a combination of the two.

Mike
 
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Reactions: Tallman, sp5it and Shadetree Mechanic
ok so you would be expecting a reading of 15w out the other end?

Well my meter is a MFJ-847 seems right or close with my TS-2000 and with 3 HT's that are ratted at 4w
The radio being tested is a 25w Kenwood TK-840 i have 4 of them and they read 23~25W

it maybe a compound of the 2.
all tests where preformed with a dummy load..
 
sp5it said:
Play with https://ac6la.com/tldetails1.html
You'll find out.
Mike
Click to expand...

I put LMR400 in and 23w in and it is saying 12.2 out... :unsure:


NefvLf7.jpg
 
sp5it said:
Your antenna have R=250 Ohm? Does not have 50 either, but should be close.
Click to expand...

ahhhh yeah i don't know how to use this program..


well my Friend has a bird meter he is going to swing by and we will test with that...
 
KD2GOE said:
Well I did a power test on 446mhz on 50'..
Testing at the radio I got 23watts
Testing at the other end I get 13w
I am loosing 10w through coax loss....
Is this excessive or something normal?

This is the coax
http://www.davisrf.com/buryflex.php
Click to expand...

According to this calculator

https://www.qsl.net/co8tw/Coax_Calculator.htm

you're about 3 watts off. That's good enough. You have to be using a dummy load for accurate readings. When I tested the lmr400 to my vhf/uhf antenna with a bird 43 I found this calculator to be very close.
 
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A little "secret" that the coax companies don't (actively) tell you is the Db loss/100 feet is into a 50 ohm load.
 
Last edited:
Well within the accuracy of most wattmeters with that reading. Even within the Bird meters accuracy.

SIX-SHOOTER
 

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