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TM-941A review by N0IVN | Radioaficion Ham Radio

TM-941A review by N0IVN

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Kenwood TM-941A Triband FM Transceiver

Three for the price of one.

review Kenwood TM-941A Triband FM Transceiver

First there were single-band FM transceivers, then came dual-band rigs. Now there's a three-band radio, Kenwood's new TM-941A triple-band FM transceiver that covers 2 meters, 70 centimeters and 23 centimeters. With this one rig you can operate on the 144,440 or 1200 MHz amateur bands.

Kenwood has managed to squeeze three transceivers into one small package measuring 5.9"W x 1,97"H x 6.89"D, It feels like three transceivers, though, weighing in at over four pounds.

What the TM-941 A Offers

The TM-941 A is designed for 13.8 VDC operation at a maximum of 11.5 amps (high power transmit on 2m). It comes with several standard accessories, including a mobile mounting bracket, DTMF microphone, DC power cable, an extra fuse, a 56-page instruction manual, warranty card, and an assortment of miscellaneous hardware. Also included is a nice feature that's recently become popular on a number of other mobile rigs: a detachable front panel. With either the optional PG-4K or PG-4L interconnect kit, the transceiver body can be located remotely from the front panel This is especially handy in some of today's cramped smaller autos, and provides an added measure of security in any vehicular installation.

Three RF output power levels are available on 2m and 70cm: hi output on 144 MHz is 50 watts, mid is 10 watts and low is around 5 watts. The power levels on 440 MHz are 35,10 and 5 watts respectively. Two power output choices are available on 1200 MHz, 10 watts (hi) and 1 watt (low).

As shipped from the factory, the TM-941 A transmit frequency ranges are 144-148 MHz, 438-450 MHz and 1240-1300 MHz. and modifications for MARS/CAP are possible. Receive coverage on 2m is 118-174 MHz (including AM reception in the aeronautical bands, although the instruction manual makes no mention of this). The 70cm and 23cm receive frequencies are the same as the transmit frequencies, but a modification is available that will expand the reception coverage to 400-475 and 1210-1330 MHz.

The three transceivers are about as separate as is possible in one radio. Kenwood has provided each band with its own volume and squelch control, antenna connection, display area on the front panel LCD. and external speaker jack. The radio's single internal speaker is common to all three bands, and there is a fourth speaker jack available that can route the three bands* combined audio to a single external speaker. You could conceivably have as many as four external speakers connected-one for each of the three separate bands, and one for the combined audio.

This separate functionality means that you can simultaneously receive on all three bands, and even configure the rig for cross-band repeat operation (I wasn't able to test this feature and there's no mention of how to do it in the instruction manual).

The Features

The TM-941 A is packed with all the features and capabilities typical in modern microprocessor-controlled transceivers. Space restrictions preclude a review of all of them (the instruction manual is 56 pages long, not including the schematic and block diagrams), so I'll highlight a few of the major ones that are either standard or are available as options.

CTCSS encoder: There are 38 subaudible tones included, selectable from the front panel. The rig I tested did not have the optional TSU-7 CTCSS decoder, but the module is easily installed in a socket accessible behind the front panel.

Dual-tone squelch system: If the optional DTU-2 module is installed, this function allows what Kenwood describes as selective calling. When activated, the receiver's squelch will not open unless the transmitting station sends a three-digit DTSS code matching what you have programmed in your radio. You can also transmit programmable codes for individual or group calling. The paging function of this option lets you display the three-digit code of the calling station on the front panel display. Seven memories are available for storing your own radio's code, the calling station's code during receive, and group codes or the codes of other stations.

Repeater offsets: Automatic offsets that conform to the ARRL's band plan are standard on 2m, but you can override this and enter your own offsets, if necessary Offset selection on 70cm and 23cm must be done manually.

Tone alert: This provides an audible alarm to let you know when someone is transmitting on a frequency being monitored. When activated, this function won't actually break squelch to allow you to hear the transmission. It just beeps when a signal is received, and keeps track of the elapsed time of the signal's transmission.

Automatic power off: How many times have you forgotten to turn your mobile rig off after you left the car? Popular in many HTs, this capability in the TM-941A will turn the radio off after two hours and 59 minutes of inactivity.

Time-out timer: If you are on the long-winded side and keep timing out repeaters, this function will be especially useful. You can select 3, 5, 10t 20 or 30 minutes (or off for no limit) as the amount of continuous transmission time allowed before the radio automatically switches back to receive mode. A beep will let you know when the rig has reached the limit you've chosen.

Automatic band change: Suppose you have the TM-941 A set to transmilVreceive on 2m. but you're also monitoring 70cm and 23cm, If you wanted to transmit ont say. 23cm you would have to manually select that band to be able to transmit on it. With the a b.o function activated, the radio will automatically do that for you when a signal on another band is received.

Automatic lock tuning: This function ts available only on 1200 MHz, and operates somewhat like an AFC. When turned on, the ALT will detect the drift in frequency of either you or the other station and automatically shift the TM-941 A's frequency to compensate.

Fixed detect output: The internal microphone connector {it's behind the front panel) is an eight-pin telephone-type jack One of its pins is labeled bd and can provide receive audio from the selected tx/rx band. By using the cont sel function, this terminal will be activated and can be used for packet operations.

Dimmer: The front panel illumination can be set to one of four levels of brightness.

review Kenwood TM-941A Triband FM Transceiver

Scanning: Here's where the magic of microprocessors really shines! The TM-941 A includes 'Band Scan," where an entire band is scanned in the VFO mode. "Programmable Band Scan" lets you scan a range between selected upper and lower frequency limits. "Memory Scan" covers those memory channels that are stored in a band or bank and have not previously been locked out. "Call/VFO Scan" alternately scans the call channel and a chosen VFO frequency, and "Call/Memory Scan" alternates between the call channel and the memory channel last used. "Auto Memory Scan" automatically memorizes a busy frequency (it's stored in an empty channel in bank five) while scanning a band. Kenwood also included two types of scan hold/resume functions: "Time Operated Scan" and "Carrier Operated Scan." In "Time Operated Scan" the radio will stop on a busy frequency for about five seconds, then continue scanning. In "Carrier Operated Scan" mode, the radio will stop on a busy frequency and remain there until the signal is no longer being received After a two second pause with no signal present it will resume scanning.

Memories: Seven pages alone in the instruction manual are dedicated to the various memory functions available in the TM-941 A and their operation. The rig includes a lithium battery to retain the memories when primary power is not available, and you can reset the main memories and VFO memories independent of each other, The radio has 100 memory channels tor each band, divided into five banks of 20 channels.

For normal channels, each memory is capable of storing operating frequency, offset, CTCSS tone and status, frequency step, shift status, REV status, OTSS code and status, and last operation paging memory number (with the optional DTU-2). For odd split channels, the same information is stored, except for shift status and REV status. A call channel memory for your favorite frequency is also available for each band.

Adjacent memory banks can be linked to form one larger bank, and all banks can be linked. It's also possible to perform memory consolidation, where memory channels are rearranged to optimize memory scan operations, This rewrites the active memory channels sequentially, from the lowest to highest channel, without any blanks in between. Memory shift will copy the contents of a memory channel to the VFO.

Miscellaneous: Kenwood has included a "Demonstration Mode" that is described in the manual as capable of providing "a short demonstration of the capabilities of the TM-941 A." I found that this was not particularly useful, since it doesn't really show how the radio works or how to use it. It's actually not much more than blinking lights and a flashing display that ends with "enjoy your hobby" before repeating all over again. When you cancel this function, the VFO memories are cleared (but not the main memories). Other features include the ability to set the beeps that the radio emits when buttons are pressed to one of eight loudness levels, including off; three radio lock functions allow disabling all of the microphone buttons (except ptt), the front panel buttons and tuning control, or all controls except the on/off switch, volume and squelch. Frequency step selection includes 5, 10,15 and 20 kHz on 2m. all of those plus 12.5 and 25 kHz on 70cmt and 10,12.5, 20. and 25 kHz on 23cm.

In receive mode the radio is specified to draw less than 1.2 amps, and in transmit mode (high power) less than 11.5 amps on 2m, 10 amps on 70cm, and 6 amps on 23cm. F3E (FM) operation is by reactance modulation, and spurious outputs are rated -60 dBc or more on 2m and 70cm, and -50 dBc on 23cm. Maximum deviation is ±5 kHz, and transmitled audio distortion is specified at 3% or less at 60% modulation.

The receivers all use double conversion. The first IF on 2m is 10.7 MHz, 70cm is 21.6 MHz, and 23cm is 59.7 MHz. All three bands use a 455 kHz second IF, Sensitivity for 12 dB SINAD is rated at better than 0.16 u.V, and squelch sensitivity less than 0.1 uV, Kenwood specifies -6 dB selectivity at more than 12 kHz on all three bands, and -60 dB selectivity at less than 24 kHz on 2m and 70cm and at less than 36 kHz on 23cm. Audio output is rated at more than 2W (8 ohm load at 5% distortion).

Antenna connections are made to the three short cables on the rear of the TM-941 A. Female UHF connectors are provided for both 2m and 70cm, and a female N connector for 23cm. The cables for the two higher bands also include plastic boots that slip over the connectors for additional protection (they're not weatherproof, however).

The front panel contains a number of controls to operate the radio. Included are a tuning control knob, volume and squelch knobs for each of the three bands, power on/off, a front panel release button, and 14 other pushbutton "keys." Many features are controlled by functions embedded in the various keys, accessible by pressing certain combinations of keys For example, pressing and holding the "F" key for about one second until the key indicator flashes, then pressing the "REV" key. enables the beep volume selection.

The front panel LCD display is quite impressive. It includes separate areas for each of the three bands, and each band display area has its own S/RF meter, on-air indicator, plus a host of symbols for the various functions that may be active on each band It s possible to completely turn off one or more of the three bands, and doing so will blank the respective area of the LCD after "off" has been displayed for about 10 seconds.

The DTMF microphone supplied with the TM-941 A has the standard 16 tones, ptt, up/ down buttons, call, vfo and mr (these three duplicate the functions of their counterpart on the radio s front panel), and a pf (programmable function) button. The pf button can be programmed to perform one of 10 transceiver functions, including a monitor function that's not on the front panel.

Test Results

Actual power consumption was comfortably less than what Kenwood specifies, At 13.8 VDC, maximum current draw while transmitting on 2m was 9,2 amps <hij, 5.9 amps (mid), and 4.28 amps (low) On 70cm the figures were 7 3 amps (HI), 3 78 amps (mid) and 2 71 amps (low); on 23cm they were 4.18 amps (HI) and 2.52 amps (low). In receive mode on all three bands, the current draw was 940 mA with the cooling fan off and 990 mA with the fan running. One departure from conventional VHF/UHF mobile rigs that I've used in the past is a small fan attached to the rear cooling fins. It comes on during transmission and shuts off automatically after a minute or two in receive mode

Using the Motorola R-2600A communications analyzer (see the sidebar). 2m receiver performance was found to be 0.15 pV sensitivity for 12 dB SINAD, 0.22 pV for 20 dB quieting, and 0.07 pV for squelch sensitivity. At 1.25 watts audio output, distortion was 1.2 percent. The receiver's performance on 70cm was equally good, with 0.17 pV sensitivity for 12 dB SINAD, 0,21 uV for 20 dB quieting, and a squelch sensitivity of 0.07 pV, At 1 watt audio output distortion was 1.3%, I was not able to make these measurements on 23cm, due to the upper frequency limit of the communications analyzer.

When I measured RF output power, I chose three frequencies in each band—one at the lower end of the band, one in the middle, and one at the upper end. The results are summarized in Table 1.

review Kenwood TM-941A Triband FM Transceiver

The purity of the TM-941A's transmitted spectrum. On both 2m and 70cm the only measurable spurious emission was the second harmonic, which was greater than 65 dB down, The Tektronix spectrum analyzer I was using has an upper frequency limit of 1800 MHz (below the second harmonic of 23cm). and within that range I could not find any spurious signals from the 23cm transmitter.

Frequency accuracy on 2m averaged a little more than 300 Hz low. and 1.3 kHz low on 70cm. I didn't measure this parameter on 23cm, Transmitter deviation with normal speech was 3 to 4.5 kHz, with the microphone two to three inches away. On-air signal reports, both simplex and through local repeaters, were rated very good by several hams. (I called up a local 2m ATV net with the TM-941 A instead of my usual rig. and received glowing reports there, too.)

Comments

Kenwood has done a nice job with this radio* Squeezing three separate transceivers into one relatively small package was a formidable task, but they did it right. Even the broadband reception capability on 2m produced few problems. I listened to signals in the aeronautical bands, public service bands, etc. and found received quality to be quite good This kind of design is sometimes susceptible to intermod. though. While monitoring certain 2m ham frequencies. I occasionally heard a paging transmitter sneak through.

The cooling fan is a nice touch; it's not too loud, but it is noticeable in the shack. In a mobile environment, vehicle and road noise easily mask it. I noticed that the radio remains warm to the touch in just receive mode, due to the amount of electronics inside the case. The temperature did not appear to increase significantly while transmitting, thanks to the cooling fan.

Very Few Complaints

I really had trouble finding things I didn't like about this radio. The use of a UHF connector on the 70cm antenna lead is not to my liking, and the demo mode in the radio really serves no useful purpose. Output power on 2 meters in the HI position was a few watts low on the rig I tested, but everything else was right about where it was supposed to be. A couple of items, like AM reception capability on aeronautical frequencies and crossband repeater operation, were not included in the instruction manual but should have been. I also noticed that the front panel latch button didn't always snap into the locked position when the panel was replaced; sometimes I had to manually lock it. The only other thing I didn't like was having to return the radio after the evaluation! The real question, though, is how long before they put this triband technoJogy into an HT?

1991 - Ron Hranac N0IVN - 73 Amateur Radio Today

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