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Interference HOW-TO
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Tuning your equipment
This page Covers How-To get 'Clear RF-Signal' and avoid transmitting 'splatter' by tuning your equipment properly.
Your Microphone
Using a power microphone is quite nice,- first you donīt have to modulate (Shout) as much your self, but usage of an power microphone can also gives problem with OVER-MODULATION.
By Over-Modulating your AF-Stage on your Transceiver you might feed 'cracked' AF into your mixer-stage and onto your RF-Stage and your output signal.
To avoid this problem - you only have to finde the maximum modulation point on your power microphone,- precede as follows.
- You need to be able to monitor your RF-Output by Watt-Meter.
- You dont have to puch more than a couple of watt,- we ar not about to test maximum output power, only trye to determain maximum modulation point for your Power-Microphone.
- Set your Transceiver to SSB-Modulation (USB/LSB) Check for a clear frequency.
- Lower the Gain on your Power-Microphone to minimum.
- Transmit 'Normal talk' - Check your Power OutPut
- Increase the Gain on your Power-Microphone, Transmit 'Normal talk' - this should give an increase on output power as well.
- Repeat the procedure untill you canīt detect any Increase to your Output power.
- At this point you have reached the point where ingrease in modulationt dont give more Output - Only OVER-Monulation.
- Lower the gain slightly to give 'safty' range for maximum modulation.
Now your set to use your Power-Microphone and to be quite shure to not over-modulate,- Now you should never increase your microphone gain above the determined level,- this gives no more gain only over-modulation and interference.
Using Power Amplifier
In general Power Amplifiers should not cause problems,- how ever this is the most common source to interference.
Why is this so? Here is some reasons.
- Bad installations as described above.
- Amplified AF-Overmodulation as described above.
- Unpropper antenna matching as described above.
Al these problems tend to get 'magnified' when also using an Power-Amplifier,- a simple fact!.
Usage of Power amplifiers also rices some new problems.
- Low quality of Power-Amplifier.
- Unsatisfiable Power supply.
- Ower-load of stage by to much input-drive.
Pore quality Amplifiers
- There is several manufactures that simply compromise the quality of thair product to cut manufacturing costs and give low-price high performance amplifiers,- this is not a good thing. low quality amplifiers is ALWAYS over rated in RF-Output value.
This problem is most obvious whit the smallest types of transistorized amplifiers.
Low quality on the Power-Amplifier does not mean that it is unusable,- you might have to reduse your expectations on maximum Output,- A low quality Amplifier can work with 100% satisfaction when not operating at rated levels,- simply reduse drive power to about 60-80% of rated maximum drive power.
- Sample:
If you got an amplifier rated to 200Watt SSB Output,- reduce input power with 60-80% of rated drive power,- you should be able to get at least 130-160 watt SSB Output with sefetey range to get interferance problems.
Power supply - You also need to use sufficient power-supply for your Amplifier,- calculate power-drain for your Power-Amplifier with the form:
[Maximum Output(Watt)]/[Used-Voltage]
- Sample:
You got a 200Watt amplifier using a 13.8V power source - equals 200/13.8=14.5 Ampere power drain maximum.
You also need about 20% of safety range - this gives that your power-supply need to be rated at about 18 Ampere surge.
Also the power-supply need to have sufficient filtering of output voltage,- if ripple is present this will contaminate your RF-Signal.
Over Load of Drive Power - You only have to finde the maximum drive point on your Power Amplifier,- precede as follows.
- You need to be able to monitor your Amplifier RF-Output by Watt-Meter.
- In this test you are about to puch MAXIMUM power from your amplifier.
- Preferably use a 'dummy-load' instead of antenna.
- You also need to be shure that your power-supply is sufficient.
- Set your Transceiver to AM or. FM-Modulation - Check for a clear frequency.
- Lower the Output on your Transmitter to minimum.
- Transmit a 'carrier' - Check your Power OutPut
- Increase the Output on your Transceiver, Transmit a 'carrier' - this should give an increase on output power from your Amplifier as well.
- Repeat the procedure untill you canīt detect any Increase to your Amplifier Output power.
- At this point you have reached the point where ingrease in Drive Power dont give more Output from your Amplifier.
- Lower the Drive power from your Transceiver about 20% to give 'safty' range for maximum drive.
Now your set to use your Power-Amplifier and to be quite shure to not over-load,- Now you should never increase your Drive power above the determined level,- this gives no more Output from Amplifier only interference.
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