MICHAEL HUGHES wrote:
> I need some help. Upon receipt of my new AL 1500 I noticed that the Multi
> Meter P.O. "Power Output" function indicated 1,100 watts output on 40 meters
> and similar low output readings on 15 meters. In all cases the load is a
> Hygain Hytower with VSWR at 1.5"1 or less on the frequencies tested. After
> talking to the factory they had UPS pick up the amplifier and it along with
> the tube were returned to Ameritron. I was given priority as it is a new
> unit. My contact at Ameritron couldn't find anything wrong with the
> amplifier and promptly returned it to me after asking question regarding my
> line voltage and whether or not I may have had the ALC connected. My drop is
> connected directly to the electrical box, 12 gage wire and the AlC was not
> connected. I asked the Technician on more than one occasion regarding the
> P.O. Multimeter and the accuracy of the Power Output and was assured that it
> was an accurate indication of power output.
>
> After receipt of the Amp it behaved exactly as it did when it left my home.
> Over the weekend I inserted an additional piece of Coax, RG 8214,
> approximately 24' long in line with the antenna and the amplifier and got
> significantly different numbers. I was driving the amplifier in all cases
> with a FT 1000mp Mark V Field with 50 watts indicated output power.
>
> The P.O. Meter now indicated somewhere between 1,500 and 2,200 watts
> depending on the band. All were checked with the exception of 160 for which
> I have no load at this time.
>
> I also used a scope, TEK 2235 connected to my EWE antenna to monitor the
> transmitted RF of both the driver and the amplifier. Using these numbers I
> extrapolated the gain in decibels, converted it to gain and multiplied the
> gain by the driver power (50 watts). Considering the drive, 50 watts the
> results seemed reasonable, if not somewhat optimistic with power outputs
> approaching 1,500 to 1,800 watts.
>
> My guess is that the power meter in the AL 1500 is really a "Relative Power
> Output" meter, not a Power Meter. The power meter reading should not be
> dependant on where you place the meter in the transmission line, or at least
> I would not think so.
>
If you have a reactive load the power readings and the power will be
different.
In cases like these it's best to check out the amp with a dummy load.
Check out the antenna(s) with a good bridge. If the lode is reactive,
changing the length of the coax will change what the meter sees. You can
verify this with a bridge.
> I am not complaining about the amplifier, overall, I would make the purchase
> again, based on cost/benefit.
>
> My guess is that this is a RF sniffer circuit which is good enough for a tune
> up process but not what I was expecting.
>
> If it is truly a watt meter then there is another problem.
>
Simple watt meters, even calibrated ones, depend on the load being the
same resistance and non reactive for them to be accurate.
73
Roger (K8RI)
> Thanking you in advance for your thoughts.
>
>
> Mike,
>
> KE9AG
>
>
>
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>
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