TASMA Technical Specifications
The purpose of these specifications is to provide guidance to the TASMA technical committee in the issuance of new coordinations and in the resolution of interference problems reported to the committee. In addition the TASMA technical committee recommends these specifications to all 2 meter repeater owners in order to prevent interference situations:
- Maximum peak deviation of the repeater transmitter should be no greater than 4.2 kHz & maximum modulating frequency of 3 kHz, with a 20 dB rolloff of the post-limiter filter at 4.4 kHz.
- Maximum transmitter frequency error: +/- 300 Hz.
- -6 dB IF bandwidth should be no greater than +/- 6 kHz, & -50 dB IF bandwidth should be no greater than +/- 10 kHz. If IF filter retrofit is needed in the repeater receiver, Com-Spec in Orange, CA (http://com-spec.com/narrow.htm) has filters for many commercial-grade receivers. These filters are designed for 12.5 kHz channel spacing and should yield exceptional 15 kHz adjacent-channel rejection. Repeater users should not be adversely affected provided they do not run excessive deviation on their transmitters. If installation of the narrow IF filter causes poor carrier squelch action, try one of the following:
- If the receiver doesn’t have a “Micor” squelch, install a Micor squelch board (available from Link Communications: http://www.link-comm.com, part # RLC-MOT), or purchase the M7716 Micor squelch IC & build your own. (Schematic – Close the schematic window by using the X in the upper right corner to return to this page.)
- Disable carrier access & use CTCSS squelch only. Use an audio delay module in your repeater controller to reduce the length of the normally long CTCSS squelch tail.
- Center the IF bandpass of the repeater receiver via adjustment of the LO frequency so that it is within +/- 300 Hz of center freq.
- Repeaters should use the minimum transmitter power necessary to reach the users.
- All new repeater coordinations will require the use of some form of selective access (CTCSS or DCS).
TASMA recommendations for repeater operation:
In addition, the TASMA technical committee recommends the following practices in order to minimize interference and maximize the utility of 2 meter repeaters:
- All repeaters located at “comm sites” (shared commercial or government communications facilities) should utilize circulators and narrow bandpass (i.e. cavity) filtering on the transmitter.
- Maximum receiver desensitization caused soley by keying of the transmitter should be no more than 1 dB.
- Where not specifically a condition of coordination of an existing fully-coordinated repeater, use of CTCSS access is highly encouraged (all new coordinations require CTCSS access). An alternative to normal CTCSS access for carrier squelch systems not wishing to prevent non CTCSS-equipped users from using the repeater is to set the carrier squelch of the repeater receiver such that only strong signals open the squelch, then use the CTCSS decoder to “pull” the carrier squelch setting down to threshold, or use “OR” squelch (either carrier squelch or CTCSS decoding will open the repeater). This latter method is implemented in several currently available repeater controllers as access mode “4”.