Cleveland RAYNET Group

Website Map    National RAYNET

FM Rigs

Back Home Up

VHF/UHF FM Rigs and the EasyPal Program

This page refers to FM rigs used with EasyPal and connected via the rig's standard data port socket.  One common standard is the 6 way mini-DIN socket.  The data port was originally intended for use with the only common data mode at that time which was AX.25 packet data.  Any analogue data mode can be and should be used by connecting to a rig's data port if it exists.

Rig menus and data port pins are often designated as either 1200 bps or 9600 bps.  For modern data modes, those designations are confusing as they don't relate.  Note that the signals on the transmit and receive pins of the data port are and always were audio signals (tones).  They never were square wave "DC" signals at 1200 or 9600 bps.

These notes specifically mention a Kenwood TM-V7E FM rig and a Yaesu FT-8900R FM rig.  The notes also apply to similar rigs.  Whether rigs are similar depends on whether the data port connections always bypass FM speech pre-emphasis circuits and de-emphasis circuits or only when rig menu 9600 bps is selected.  That can be discovered either by examining circuit diagrams or by testing a rig with another which has a known flat audio response on both transmit and receive.

Rig Data Port

A few important points about a standard data port are:-

The standard varies!
The audio signal voltage level at the receive audio pin is not under the control of the rig's normal audio volume control.  The audio level will vary as the amount of FM deviation changes on the received signal.
The audio signal voltage level at the transmit audio pin has no volume control (see later about a menu switch).  It expects a certain range of audio signal level and will modulate the RF carrier with a value from 0 kHz to the maximum FM deviation allowed by the rig, typically +/- 5 kHz or +/- 2.5 kHz. The FM deviation level will depend on the signal level of the transmit audio signal from the sound card.
The data port has one transmit audio pin.
The data port has two receive audio pins.  One is designated 1200 bps and the other 9600 bps.  They both have receive audio, even though the rig menu may be set to the opposite data speed.

Rig Bandwidth Menu

Some rigs with a data port have a menu to change the receive bandwidth.  In general, the wider bandwidth is usually best.  The Kenwood TM-V7E and similar FM mobile rigs has a fixed receive -6 dB bandwidth of 12 kHz and so there is no menu option to change bandwidth.  The Yaesu FT-8900R has two -6 dB bandwidths: 12 kHz and 15 kHz.  The 15 kHz bandwidth always gives the best results when receiving data files.  FT-8900R menu 43 = WIDE.

Rig Data Rate Menu

Rigs with a data port have a menu setting to change between 1200 and 9600 bps.  Instead of bits per second, it could be called Baud (Bd) and the plural of Baud is still Baud.  As mentioned above, these historical speed designations are unfortunate and confusing.  EasyPal in DRM mode A has a data rate of 6360 bps, which is neither 1200 nor 9600 bps.

What should be the modern designation of these menu options?  It isn't easy to answer.  With Kenwood rigs, it could be "Low transmit audio level" and "High transmit audio level".  With Yaesu rigs, it is more complicated.

Kenwood TM-V7E menu 1.5 = 1200:-

  1. The data port pin 1 (transmit audio) expects a signal in the region of 14.1 mV RMS to give a reasonable FM transmit deviation.
  2. This transmit audio pin bypasses FM speech filters and so has a flat audio response.
  3. Data port pin 5 (1200 bps receive audio under squelch control) can be used or pin 4 (receive audio always open squelch).
  4. Both receive audio pins bypass FM speech filters and so have flat audio responses.
  5. Either receive audio pin will give a signal level of about 177 mV RMS.

Yaesu FT-8900R menu 26 = 1200:-

  1. The data port pin 1 (transmit audio) expects a signal in the region of 14.1 mV RMS to give a reasonable FM transmit deviation.
  2. This transmit audio pin does not bypass the FM speech filters when 1200 is selected and so has a rising audio response slope.
  3. Data port pin 5 (1200 bps receive audio under squelch control) can be used or pin 4 (receive audio always open squelch).
  4. The 9600 bps receive audio pin bypasses FM speech filters and so has a flat audio response.  The 1200 bps receive audio pin does not and has a falling audio response slope.
  5. The 9600 bps receive audio pin will give a signal level of about 177 mV RMS.  The 1200 bps receive audio pin will give a signal level of about 106 mV RMS.

Although both rigs seem to have a standard 6 way mini-DIN data port socket, there are serious differences in standards.  The pin placements are the same in the plug or socket, so data modes can be used with either rig by swapping plugs from one rig to the other.  The data rate menu settings have different effects.

Kenwood TM-V7E menu 1.5 = 9600:-

  1. The data port pin 1 (transmit audio) expects a signal in the region of 707 mV RMS (50 times louder than 14.1 mV) to give a reasonable FM transmit deviation.
  2. This transmit audio pin bypasses FM speech filters and so has a flat audio response.
  3. Data port pin 5 (1200 bps receive audio under squelch control) can be used or pin 4 (9600 bps receive audio always open squelch).
  4. Both receive audio pins bypass FM speech filters and so have flat audio responses.
  5. Either receive audio pin will give a signal level of about 177 mV RMS.

Yaesu FT-8900R menu 26 = 9600:-

  1. The data port pin 1 (transmit audio) expects a signal in the region of 707 mV RMS (50 times louder than 14.1 mV) to give a reasonable FM transmit deviation.
  2. This transmit audio pin bypasses FM speech filters when 9600 is selected and so has a flat audio response.
  3. Data port pin 5 (1200 bps receive audio under squelch control) can be used or pin 4 (9600 bps receive audio always open squelch).
  4. The 9600 bps receive audio pin bypasses FM speech filters and so has a flat audio response.  The 1200 bps receive audio pin does not and has a falling audio response slope.
  5. The 9600 bps receive audio pin will give a signal level of about 177 mV RMS.  The 1200 bps receive audio pin will give a signal level of about 106 mV RMS.

Receive Audio Level

The receive audio level into the sound card makes virtually no difference to EasyPal's ability to decode a data file as long as it is not zero.

Best Settings and Practical Problems

From the point of view of a flat audio response for data transmission and reception, the Kenwood TM-V7E and similar rigs are better, as the 1200 and 9600 bps menu settings always have a flat transmit and receive audio response.  The Yaesu FT-8900R and similar rigs have a flat transmit audio response only when 9600 bps is selected.

Problem 1: EasyPal is a data file transfer program using either the PC's sound card or the sound card inside an external data interface box.  PC sound cards usually can't supply a high enough transmit audio level to the rig's data port pin.  They can always supply the 14.1 mV RMS required with the 1200 bps menu setting.  They usually can't supply the 707 mV RMS required with the 9600 bps setting.  If a PC's sound card was designed to feed its output to a loudspeaker, there would be no problem.  Modern PCs usually have a headphone socket which is designed for either external headphones or for connection to an external audio amplifier feeding a loudspeaker.

Problem 2: The data interface cable or box used for EasyPal may also be required for use with other equipment or for another data mode which works best with different conditions.  Two examples are the same data interface also used with APRS and with the CRASH program.

Kenwood TM-V7E used with EasyPal and the PC's Sound card: Select menu 1.5 = 1200 bps.  Connect to pin 1 (transmit audio).  It will have a flat audio response.  Connect to either pin 4 (9600 bps receive audio) for open squelch audio or pin 5 (1200 bps receive audio) for the audio to be under squelch control.  Either will give a flat audio response.

Yaesu FT-8900R: Select menu 26 = 1200 bps.  Connect to pin 1 (transmit audio).  It will have a rising audio response.  Connect to pin 4 (9600 bps receive audio) for open squelch audio with a flat audio response.

Yaesu FT-8900R: The SignaLink contains its own sound card.  Insert jumper JP3 to increase the transmit audio about 50 times.  Select menu 26 = 9600 bps.  Connect to pin 1 (transmit audio).  It will have a flat audio response.  Connect to pin 4 (9600 bps receive audio) for open squelch audio with a flat audio response.  If this SignaLink is then connected to a Kenwood TM-V7E rig, it will work fine when menu 1.5 is set to 9600 bps.

Switching the Receive Audio Pin

The above settings will give the best EasyPal data file transfer results.  If the same data interface cable or box is used with APRS or the CRASH program, unsquelched receive audio noise may cause serious problems.  To make a data interface unit most useful, it is best if it has a switch to select receive audio from either data port pin 4 or 5.  That should be very easy for a home made data interface.

For a SignaLink data interface, modifying a commercial product may not be desirable by some.  Instead of using a switch, two cables between the SignaLink and rig's data port could be obtained.  One to use pin 4 and the other to use pin 5.  For flexibility without modifying the SignaLink box, a switch could be inserted in the cable instead.  If the SignaLink is used with jumper JP3 in circuit to increase its transmit audio 50 times, a switch may be required to open JP3 for use with other equipment.  Less conveniently, for different uses, the SignaLink can be opened up using a hexagonal 3/32" Allen key (a Torx T-10 also fits) and jumpers moved with pliers.

_________________________________________________________________________________________________
You can send an e-mail message to Cleveland RAYNET Group by clicking here.   This will fail if you use web-based e-mail.
Page updated on 09 January 2017

website statistics