Adjusting Orion AM Output Power

From the Orion Reflector August 16, 2013

A while back I posted regarding a problem that I was having with a newly acquired Orion 565 on AM mode. I received no replies. It appears that I have found what caused the problem and many (I mean many) Orion 565's and 566's may have the same problem but it goes undetected because not that many people with an Orion, works AM! It is part of a larger problem however.

The RF output sensor circuit is pretty straightforward using a toroid and some diodes and other parts. It feeds the meter and generally indicates power output and SWR for the transmitter. The built in processor also references this circuit when automatically setting the AM carrier power to 25 watts.

The diodes are in a part of the radio where they can be affected by many things, including static damage from having the antenna connected during a storm etc. I found the readings on my front panel meter to be correct when indicating 100 watts output when checked on a dummy load and a known good external wattmeter, however, way off when reading lower power.

The radio worked well on SSB and CW but when I switched to AM, the radio would produce no more than 3 to 5 watts of carrier. TT service pointed to the very expensive data board as a probable fix and at $625 I could take the chance with no guarantees.

I worked on this for a couple of months and even found a procedure on the TTWiki for setting the "RF""SWR" and "ALC" pots but kept ignoring it. It seemed that the processor must get some indication of rf power output from somewhere but I kept thinking about the 100 watt reading was right on.

One day, I just got a wild hair and connected a dummy load and a known accurate wattmeter to the Orion and started at it. The procedure that I referenced didn't seem to make a lot of sense so I took a common sense approach to it.

I set the PWR/Multi control to 100 and saw 100 watts on the external wattmeter and on the Orion panel meter. No surprise but when I began to reduce the PWR/Multi control the readings below about 80 watts were very far off. Resetting the calibration of that meter with the "RF" control on the board under the speaker inside the Orion was quite interesting. I first set the output to 50 watts on the external wattmeter and then set the control so that the panel meter said 50 watts. Interestingly, the power output readings were very accurate up to 80 watts and as the transmitter power was increased beyond that, the meter kept indicating 80 watts.

Now the cute part. When the Orion was placed into the AM mode and keyed … the processor set the carrier to 20 watts! That's not far from the 25 watt spec, the way it was supposed to act.

There was an earlier post today regarding problems with the power output indications and cleaning and resetting those same 3 pots. I emailed Thomas and found that his Orion II is now putting out a 10 watt carrier after he readjusted those pots. Not good! There is a documented procedure on the TTWiki but it is vague and not easy to follow and says nothing about the affect of those adjustments on AM operation.

My guess is that many Orion owners will experience totally normal operation of their transceiver but if they tried the AM mode, they would see carrier outputs all over the place, many times making the radio unusable on AM. This may be OK up until you sell the radio to an AM'er!! In my case 3 watts of carrier wasn't enough to drive any amplifier I own to usable power levels and don't underestimate the Orion's AM capabilities. It is very very good.

I have been using mine on AM for the past couple of weeks and it's working great now! Google and Bing have become close friends as a result of this problem but there is no information on the internet about this adjustment. I could have saved many hours of troubleshooting and work had this been well documented. I hope this helps!

73–Larry W9MDX

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