Epson MFJ-1278B manual Radio Setup for HF Packet Operation

MFJ-1278B MULTI-MODE ADVANCED OPERATION

DETAILED HF PACKET OPERATION

Here we will go into further detail on the HF Packet mode of operation. We will discuss modem center frequency, HF tuning indicator, etc. So without any further delay lets get into HF Packet operation.

Radio Setup for HF Packet Operation

Setting up your Radio interface will follow exactly the same procedure as for VHF NBFM operation with the exception that you will probably not need to set the modem output level. This is because linear mode radios typically have a transmit audio level control on the front panel and an indicator that tells you when you have set the level correctly. You will adjust the audio level just as you would for SSB operation.

If you are using an auxiliary audio input connector, such as an accessory port, you MAY need to adjust the transmit audio level from the MFJ-1278B modulator. This is because many auxiliary audio inputs are intended for phone patch audio. These levels are typically much higher than microphone levels. If you do adjust the output level of the MFJ-1278B to a relatively high value for this type of application, do not operate the MFJ-1278B with a VHF NBFM radio unless you take steps to assure that the audio level for the FM radio will not produce excessive deviation. If both radios are to remain connected to the MFJ-1278B, you can set the audio level for each radio independently by using the audio output level adjustments, R157 & R158, on the left side of the MFJ-1278B with a small screw driver.

The modem center frequency used by the MFJ-1278B for all of the narrow shift AFSK modes including HF packet operation is 2210 Hz (2125 and 2295 Hz tones). Most frequencies listed for packet operations in the HF bands were established using a modem center frequency of 1700 Hz (1600 and 1800 Hz tones) in lower sideband mode. This is a 520 Hz offset (2220-1700) between the two modem standards. So a listed frequency of 7093, for example, will cause you to have a frequency display on your radio of 520 Hz PLUS the listed frequency (IF you are also using lower sideband mode). Thus you should find the 7093 KHz packet activity centered around 7093.52 KHz.

Your tuning indicator, when properly centered, is easily capable of 10 Hz alignment accuracy per segment. It should be used as the tuning reference on any individual signal regardless of the frequency indicated on the radio dial.

NOTE: The signal actually transmitted by your SSB transceiver ( F(emission) ) when using the MFJ-1278B for AFSK HF packet operation using lower sideband will cover a band of frequencies approximately 400 Hz wide and centered at the transmitter indicated carrier frequency (F(ind)) minus the modem center frequency (Fc).

So you would use: