Vertex Standard FT-1000MP manual Wide Band and Tuned Preamp Selection, Dealing with Interference

OPERATION

DEALING WITH INTERFERENCE

The MARK-VFT-1000MPincludes a wide range of special features to suppress the many types of inter- ference that may be encountered on the HF bands. However, real world interference conditions are con- stantly changing, so optimum setting of the controls is somewhat of an art, requiring familiarity with the types of interference and the subtle effects of some of the controls. Therefore, the following information is pro- vided as general guidelines for typical situations, and a starting point for your own experimentation.

The MARK-VFT-1000MP’s interference-fighting circuitry begins in its “RF” stages, and continues throughout the entire receiver section.

VRF (VARIABLE RF FRONT-END FILTER)

The VRF feature allows you to engage a narrow band-pass “preselector” filter into the receiver’s RF cir- cuit path. The added selectivity can be a tremendous help in minimizing potential interference from strong out-of-band signals, especially in a multi-transmitter operating environment.

To activate the VRF feature, press the [VRF] button on the Shuttle Jog, then turn the VRF/MEM CH knob to peak the signal or background noise level. When the VRF feature is en- gaged, the red “VRF” LED, located on the left side of the VRF/MEM CH knob, will be illumi- nated.

If a potentially-interfering signal is very near your cur- rent operating frequency (for example, an SSB station operating near 3.80 MHz while you are on 3.52 MHz), additional protection may be realized by deliberately mis- tuning the VRF so as to place more “roll-off” of the undesired signal. In this example, tuning the VRF for peak response at 3.40 MHz will cause additional at- tenuation to be placed on the strong signal at 3.80 MHz. Particularly on the lower frequency bands, there will be no loss of useful sensitivity with moderate de-tuning, but interference rejection will be significantly enhanced.

FRONT END SELECTIONS:

AMP SELECTION, IPO & ATT

The best receiver front-end selection will depend on background noise at the time, the presence or ab- sence of strong signals, and whether or not you want to hear very weak signals. If the front end is set for too much gain, background noise will make listening diffi- cult, and very strong signals on other frequencies may cause intermodulation interference, masking weaker signals. On the other hand, if the front end is set for too little gain (or too much attenuation), very weak sig- nals will not be heard.

When evaluating the selections below, remember that if you can hear band noise increase when your antenna is connected, you have adequate sensitivity; any further early-stage gain is not needed.

“Wide Band” and “Tuned” Preamp Selection

Three high-performance FET RF amplifiers are uti- lized in the MARK-VFT-1000MPreceiver front end. A single wide-band amp is provided for good general all- around performance, along with dual tuned amplifiers: one optimized for 24~30 MHz, the other for 1.8~7 MHz (see illustration). The Tuned preamp is especially use- ful when operating from a quiet location on 10 meters, while on the low bands the Tuned preamp’s low gain provides optimum strong-signal performance. Each amplifier is selected automatically as you tune or change bands; however, you can disable the tuned amplifier pair and only use the wide-band amp via menu selection 8-4.

Note that the Tuned preamp only operates in the 1.8~7 and 24~30 amateur bands. If you tune outside of an amateur band while using the Tuned preamp, the transceiver will automatically switch over to the “Flat” (Wide-band) preamp. The effects of this design are:

(1) When tuning outside of a low-frequency amateur

Receiver Front End Configuration

(for illustrative purposes)

page 44 MARK-V FT-1000MP Operating Manual