There are several manufacturers of CW pulsers (amplifier tuning aids), but as of this date there is only one who can supply a fully constructed (or in kit form) SSB pulser. It is known by many today as the 3898 Pecker available only at www.3898pecker.com.
One of Amateur Radio's most overlooked devices today is a SSB mode amplifier tuner called the "3898 Pecker". This is the same circuit formerly known as the Fox Tango "Pulsar" (no longer available from F.T.) www.foxtango.org , or a "Woodpecker".
This circuit is nothing new; it has been around for over 30 years. Amateur Radio Operators and avid amplifier builders in the U.S., around the world are giving recognition to the benefits of tuning their amplifiers with this type of a tuner. This device is like the CW pulsers that have become popular over the last few years, in the fact that it does a rapid pulse of the transmitters out-put during operation. But that's where the similarity ends. With the transmitter and amplifier in the SSB mode (not CW), the 3898 Pecker uses a pulsed single tone, sent through the transmitters audio in-put circuit. With a pulsed tone, along with all of the equipment being tuned set in SSB mode, there is no need for multiple steps of increased RF drive during tune-up as there is while tuning in the CW mode. As well, there no need for the re-tuning (or touching-up) when changing from the CW tune-up over to SSB operation.
When tuning amplifiers in what was "the normal way", the operator would start out with a very low amount of CW or AM RF drive. Then after adding a small increases in drive each time, the operator repeats this process again, and again, until full out-put of the amplifier has been achieved. All during the tune-up process the operator has to make sure not to stay "keyed down" for very long while adjusting the Plate and Load controls. Knowing that being keyed down to long (or possibly by adding too much drive) can be disastrous to the tubes in the amplifier, as well as other costly components.
With a CW Pulser, the amplifier tune-up time is reduced, as well as some of the possible dangers of an overly long key down. But remember, the amplifier is still being tuned in CW, and should be used only for CW operation, not SSB. The CW tuners plug directly into the CW jack of a transmitter. Then when turned on, (depending on the W.P.M. setting) it produces a series of short rapid carriers or "CW Dits. The same thing can be done with the automatic CW keyer that already comes built-into many of the new radios on the market today. Unfortunately, for operating in the CW or AM mode, using CW or AM drive is still the correct procedure. In this case, a CW type of tuning device would be the faster, and most likely safest, way to tune. But still, is it the best way to tune your amplifier for SSB operation?
Once the amp is tuned in CW, isn't it tuned good enough for SSB mode anyway?
The following should be the obvious answer to that question. Most operators' find that once they change from CW to SSB mode, they still need to adjust their amplifier controls (slightly) one more time. This is to bring the Grid current back down once again and RF out-put back up to what was shown on the meters after the full CW tune-up. This alone should show that the amplifier was not properly tuned for the SSB mode. If this final adjustment has not been made, then there is still unnecessary heat and stress on the tubes and other components, as well as the possibility of illegal spurious emissions being transmitted while the amplifier is in use. The circuit consists of a 7413 dual Schmitt trigger chip, and a few passive components. One half of the chip generates an audio tone, which is switched on and off at a lower frequency by the other half of the 7413. This sends a series of tone pulses (about 1.8KHz) to the microphone input. This signal can be used for tuning your Linear Amplifier at full power, without causing any damage due to being out of resonance etc. Even though the tone can drive the amp to full output, it does so only for the duration of the short pulse, the actual "duty cycle" being determined by the ratio of the tone pulse time, to the "off" time between pulses. (Note: Most operate at a fixed 30% on & 70% off duty cycle. The duty cycle varies slightly do to variations in the values of the components used.) This short duty cycle allows you to take your time on tune-ups with very little chance of tube damage, or power supply stress, as well as the chance of arc-over within your amplifier, unlike what can happen at times using a CW or AM carrier. Please note too, that with such a short duty cycle, a Peak Reading watt meter is recommended in line after the amplifier to aid in tuning, and to show the true SSB RF out-put of the amplifier.
I hope this has helped answer some of the questions related to the controversy over CW & SSB amplifier tuners. Now the only question you should have is which type of tuner is best for your mode of operation. |
