I would suggest that it would be better to check the accuracy of the
wattmeter if the amp was fed directly into a dummy load. The Hy-Gain 18HT
Hy-Tower vertical is not necessarily a good 50 ohm feed (even though the swr
indicates that it's in the ball park) and by adding some coax into the feed
line, your amplifier was seeing a better load.It's quite likely that putting an
antenna tuner in line that you will likely get more accurate readings.
----- Original Message -----
From: "Roger" <firstname.lastname@example.org>
Sent: Sunday, October 04, 2009 8:12 PM
Subject: Re: [Amps] AL 1500 P.O. Meter Function
> 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
> 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.
> Roger (K8RI)
>> Thanking you in advance for your thoughts.
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