Hi Skipp, I can't really tell if you are agreeing or disagreeing. :>)
A good, properly tuned isolator will absorb all reflected power that is of any consequence. In other words I don't think that you would be able to see any reflected power on the wattmeter from the isolator. A wattmeter in line with the load on the circulator could be compared with the reflected power meter reading in the antenna line. Or return loss of the antenna port on the isolator measured. Given that there is no reflected power from the isolator there will be no re-reflected power going back up to the antenna therefore the amount of reflected power on the line will subtract from the power that is available to be radiated. Without an isolator in place most of the re-reflected power is available to be radiated. With a Bird inline wattmeter it will give true forward power by subtracting reflected power from indicated forward power. It will do this regardless of the impedance of the line it is installed in. When connected to a transmitter without an isolator, if there is 10 watts of reflected power and a true 100 watts of power coming out of the transmitter, the Bird meter will read 110 watts forward and 10 watts reflected. Subtracting the reflected from the indicated forward power gives a net of 100 watts power going to the antenna to be radiated. This is of course less feed line losses. Also the small amount of re-re-reflected power from the original reflected power (second trip for the reflected) which will probably be too small to measure. The same Bird meter connected to the same antenna line but with the transmitter having an isolator should read 100 watts forward and 10 watts reflected. Subtracting the reflected from the forward should give a net power of 90 watts going to the antenna to be radiated. This time the load on the isolator will be absorbing the reflected power rather than it going back up to the antenna. All wattmeters may not work the same as the Bird in regards to reflected power. 73 Gary K4FMX > -----Original Message----- > From: [email protected] [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of skipp025 > Sent: Thursday, June 05, 2008 12:32 PM > To: [email protected] > Subject: [Repeater-Builder] Re: Folded Diploles or Vertical antenna/Power > Readings > > > This is not entirely true. A transmitter with an isolator on > > it will absorb all the reflected power that reaches it. > > Not true... a circulator or isolator will deal with much of > the reflected power... but probably never all of it. > > > > > Note that forward power can sometimes read higher than > > > > true if there is more reflected power. > > What you actually read or see on a meter depends on a number > of issues... like the type of sample unit and where it is > in the feedline. > > > > > And to answer something that one person came up with a > > > > while back, decreasing the reflected power does not add > > > > it to the true radiated power. > > Yep, just depends on where it's actually going. A good match > at the power amplifier outpu presented by inserting a circulator > or isolator doesn't tell you the antenna is in good condition > or the power is actually heading out the door (the antenna). > > cheers, > s. >
