Vertex Standard FT-1000MP IPO Intercept Point Optimization, AGC Automatic Gain Control Selection

OPERATION

DEALING WITH INTERFERENCE

band (for example, tuning from 1.999.99 MHz to 2.000.00 MHz), the higher gain of the “Flat” preamp will cause the background noise to increase sud- denly (and decrease again if you tune back inside the 160-meter band).

(2)When tuning outside of a high-frequency amateur band (for example, tuning from 28.000.00 MHz to 27.999.99 MHz), the higher gain of the Tuned premap will cause the background noise to de- crease suddenly (and increase again if you tune back inside the 10-meter band).

(3)When operating on the 14 MHz band, the Tuned and Flat preamps have basically identical gains. Very little difference in performance will be observed, inside or outside the 20-meter band.

IPO (Intercept Point Optimization)

Normally, the front-end FET RF amplifiers provide maximum sensitivity for weak signals. During typical conditions on lower frequencies (such as strong overloading from signals on adjacent frequencies), the RF amplifiers can be bypassed by pressing the [IPO] button so the green LED is on. This improves the dy- namic range and IMD (intermodulation distortion) char- acteristics of the receiver, at a slight reduction of sen- sitivity. On frequencies below about 10 MHz, you gen- erally will want to keep the [IPO] button engaged, as the preamplifiers are usually not needed at these fre- quencies.

ATT (RF Attenuator) Even with the IPO function on, ex-

tremely strong local signals can still de- grade reception. So if you still notice the effects of overloading, or if the signals you want to listen to are very strong, you

can use the ATT selector to insert 6, 12, or 18-dB of RF attenuation in front of the RF amplifier. If background noise causes the S-meter to deflect on clear channels, turn the ATT selector clockwise until the S-meter drops to about S-1 (the white area at the left end of the top meter scale). This setting optimizes the trade-off be- tween sensitivity and interference immunity. Also, once you have tuned in a station you want to work, you may want to reduce sensitivity further (or add more attenu- ation) by turning the ATT control to a more clockwise setting. This reduces the strength of all signals (and noise) and can make reception more comfortable, im- portant especially during long QSOs.

When looking for weak signals on a quiet band you will want maximum sensitivity, so the IPO should be disabled and the ATT selector should be set to “0.” This situation is typical during quiet times on frequen- cies above 21 MHz, and when using a small or nega- tive-gain receiving antenna on other bands.

AGC (AUTOMATIC GAIN CONTROL) SELECTION

When tuning around the band look-

ing for signals, the AGC selector is usu-

ally best kept in the “AUTO” position, where AGC decay is automatically se- lected according to the operating

mode. You can manually select re-

ceiver AGC; however, a few points about AGC and re- ceiver recovery time need to be pointed out.

For SSB reception, the “FAST” position allows the receiver gain to recover quickly after tuning past strong signals or when fast fading occurs. However, once you have a station tuned in, reception will usually be more comfortable if you switch to the “SLOW” position (keep- ing the receiver from picking up low-level noise during pauses in speech).

For CW reception, when several signals are present in the passband, the “FAST” position can avoid AGC “pumping” (gain fluctuations) caused by strong undesired signals.

For AM reception, the “SLOW” position is usually better, and for 300-baud packet and RTTY/AMTOR, the “FAST” or “OFF” positions will usually give the few- est errors/retries.

RF GAIN SETTING

When tuned to a moderate strength signal, if low level background noise is still present after setting the ATT selector, try reducing the RF GAIN control from the fully clockwise position. This reduces the signal input to the first mixer via a PIN diode attenuator and causes the minimum S-meter reading to move up he scale, often clearing up the background noise and put- ting the desired signal more “in the clear.” Remember, however, to return this control fully clockwise when you want to receive weak signals, or read low levels on the S-meter. Also read the box on this page.

Note on AGC

The AGC “OFF” position disables the overload-pro- tection normally provided by the AGC circuitry. If the RF GAIN control is left fully clockwise in this condition, the RF and IF amplifiers can be easily overloaded (causing distortion) when a strong sig- nal is received. Correct the overload either by set- ting the AGC selector to another position, or by turning the RF GAIN control counterclockwise to set receiver gain to a comfortable level.

MARK-V FT-1000MP Operating Manual page 45