[Amps] AL 1500 P.O. Meter Function

[Fern]

       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. 
       Fern

----- Original Message ----- 
From: "Roger" <sub1 at rogerhalstead.com>
Cc: <amps at contesting.com>
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 
> 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
>>
>>
>>