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Measuring line and connector loss

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KTCS

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#1
Dear all

I have some long lines of LMR600 of approx ~120ft for 800mhz and 150mhz monitoring,, want to be able to caclualte DB loss for antenna to the rig,
rule of thumb we can say X db of loss per ft of ZZZ type of cable and add so much for each connector of ZZZ type etc, however this is still a guess,,

I want to *know* what the loss really is., what kind equipment would I need to really test or measure for this,

and what is the basic concept behind this? xmit so much power down the line and measure it at the other end?

THanks and sorry for the dumb question
 
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#2
Yes, measuring the power at the input, then at the output end of that feed line will certainly tell you how much is lost in the feed line.
- 'Doc
 
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#3
Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

A more expensive option is an anrtisu site master. Although they are a bit on the pricey side they do Return loss measurements
 

MOGA

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#4
I *think* some of the amateur radio antenna tuners for VHF/UHF will also calculate line loss in the range of frequencies in which scanners operate. I imagine that figure would be a composite of connector and feed line losses at X frequency, however.
 
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#6
...want to be able to caclualte DB loss for antenna to the rig,
rule of thumb we can say X db of loss per ft of ZZZ type of cable...
You can also look up the manufacturers specifications and determine what the loss is supposed to be. It's usually rated in db of loss per 100 feet, or 100 meters, and by frequency.

and add so much for each connector of ZZZ type etc, however this is still a guess,,
Use quality connectors and install them correctly and you can disregard connector loss. Below 1000 MHz, it'll be something on the order of 0.1 db per connector, if it's working right.

I want to *know* what the loss really is., what kind equipment would I need to really test or measure for this,
You'll need a signal source of known output power, and an accurate means of measuring it at the other end.

Actual measurements are usually beyond the scope of the typical consumer, you're going to be pretty close by using the manufacturers specs and disregarding the connectors. Accurate test equipment can be quite expensive.
 
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#7
With LMR-600 at those freqs the answer is Not Much :)

Proper tools to measure the exact loss of a particular install are expensive. Measuring loss of the coax and connectors is not the issue, its measuring the total transmission loss via radiated power from the antenna factoring in feed line transmission loss and antenna gain that is fun.
 
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