The II Morrow SL 40 Comm Transceiver

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What could be more ho-hum than a panel-mount comm transceiver? If it's II Morrow's new slimline SL 40 radio, don't be so sure. Our shop recently installed one in an AVweb member's Cessna and found out that this isn't just your run-of-the-mill comm.

ProductOur shop, Avionics West, sells handheld avionics and headsets over the Internet on AVweb. Our satisfaction guarantee policy has always been straightforward: if you don't like the product, return it within 30 days and we will sell you a different item or refund your purchase price, whichever you prefer, no questions asked.

Recently, an AVweb member asked me if this same policy applied to a panel-mount radio he was interested in the II Morrow SL 40 if we installed it in his aircraft. This was the first time I'd had the opportunity to sell panel-mount avionics via AVweb and install it in a customer's airplane. I told the customer that yes, our usual 30-day money-back guarantee would apply. I felt this was a good opportunity to install our first SL 40 and see if the product lived up to the expectations of the customer and what II Morrow claimed it will do. The downside was that if the customer wasn't satisfied, I had to refund the price of the SL 40! I decided to accept the challenge.

Company Background

II MorrowAvionics West has been selling II Morrow panel-mounts for years. The company pioneered low-cost easy-to-use LORAN "C" units such as the 612B, 618TCA and various other user-friendly models. Later, they started making low-cost panel-mount GPS receivers such as the FlyBuddy, 2001, and most recently the new GX-55.

The Salem, Oregon-based company was founded by Chuck Morrow, but some years ago he sold out to a company called UPS. You may have heard of them. My understanding is that UPS had decided to undertake an extensive vehicle tracking system for their huge fleet of brown trucks, and liked II Morrow's technology so much that they decided to buy the company. (I wonder if the folks in Salem have to wear those brown uniforms?)

Since the UPS acquisition, II Morrow has grown from a medium size company to a large organization. Years ago, I used to know just about everyone who worked there by name. It's definitely different there nowadays. I remember the days when a real person would answer the telephone instead of a computerized voicemail system! In all fairness, our II Morrow rep is Wayne McGee and I've found him to be very helpful. But I still hate their automated phone system because it seems to me that the first person you talk to should at least have a pulse. Maybe that's just me.

As I said, II Morrow is known for LORANs and GPSs. Some years back, II Morrow did introduce a VHF comm but it didn't sell too well because of the market in those days. II Morrow was competing with King, Narco and Terra, and back then those three manufacturers had the market pretty well sewed up because they had a great product and excellent dealer/owner rapport. There just wasn't enough room in the market for the new II Morrow comm. In addition, that first II Morrow comm radio didn't really have any bells and whistles to set it apart from the pack. So it pretty well died on the vine.

Things are different today. In my opinion, Narco has alienated itself from both its dealers and its customers. Terra fell on hard times and has now been purchased by Trimble, so we shall have to see what happens there. Bendix/King (now gobbled up by AlliedSignal) still produces a great product when you can get it, but lead-times are terrible on most King radios. Also, for all intents and purposes, King is still selling the same nav/comms today as they did in 1981, at least as far as features go.

Units in stock, new features and fair prices are what the aircraft owners want today, and II Morrow has apparently decided to fill that niche. My crystal ball tells me II Morrow is working on development of a full line of state-of-the-art avionics for piston aircraft. Who knows what great things those squirrely software engineers in Salem are dreaming of at night?

II Morrow SL 40 comm

Out with the Old...

The SL 40 arrived (via UPS!) the same day the customer showed up with his airplane for the installation. The aircraft was a Cessna 152 with a 28-volt electrical system. The owner told me that the factory-installed "Cessna-crafted" RT-385A nav/comm had been a problem child for the three years he'd owned the aircraft. In fact, radio repairs had been costing him more than airframe and engine maintenance. This didn't surprise me...I know Cessna radios.

I also persuaded the customer to let us remove his SPA-400 intercom system which seemed to be a basket case. When using multiple brands of headsets, the audio level would drop too low for one pilot to hear the other over the intercom. If both headsets were of the same brand, the SPA-400 seemed to work marginally. It also seemed to pick up alternator noise at low RPMs.

So out came the old nav/comm radio and intercomm. We removed all the wiring down to the circuit breaker and removed the aircraft jacks. We were getting ready to install the new II Morrow SL 40 together with a reconditioned II Morrow 2001 GPS. The VHF comm antenna and coax were replaced, proper circuit protection was installed and the GPS antenna was installed. Now was the time to open up the SL 40 box. The radio was received in good condition, thanks to UPS and some good protective packaging. We found the SL 40 to be well protected inside of anti-static wrapping. II Morrow provides a "Package Contents" that lists everything that should be inside the box, and fortunately everything was there.

...And in with the New

Our measurements showed the SL 40 to be just 1.30" high, 6.25" wide, and 11.45" deep. The width is industry standard, but in its other dimensions the unit is very small. I wondered whether I be able to read the display of this tiny thing? But avionics shops love small radios, because it means we can install more before we run out of panel space! Weight of the SL 40 was a stingy 2.1 pounds. Heck, I've eaten hamburgers that weighed more than that ("after cooking" of course). The SL 40 also meets every relevant TSO and FCC reg. The knobs and buttons have a satisfying feel. So far, so good.

Next step was to thumb through the installation manual. What a treat! The installation manual is one of the best I've ever seen. I have no doubt II Morrow hired an actual avionics installer to write the manual, because no ivory-tower engineer could have written a manual like this. The print is big and in plain English, perfect for a nearsighted wrench swinger like me. The wiring diagrams are excellent, easy to read. I have no doubt that any home-builder or A&P could easily install the SL 40, and perhaps that's what II Morrow had in mind. The instructions clearly call out the use of shielded wiring where it's required by the wiring diagram. I reviewed the diagrams and installation steps looking for mistakes, but I couldn't find any. You'd really have to try hard to screw up this installation.

The pins in the "D" connector are the crimp type and a special tool is required to do the crimping. This isn't normally a problem because almost any avionics shop has the necessary crimping tools. I've found the crimp pins are more reliable than soldered ones. If you need to install this radio and don't have the proper tool, a solder-type "D" connector could be used, but it's not provided by II Morrow and should only be used as a last resort. II Morrow even supplies the Allen wrench used to install and remove the radio from the rack. I found the rack assembly is strong and of high quality.

A Look Inside

Before installing the SL 40, I couldn't resist the temptation to open it up and have a look inside. Off came the covers and the faceplate. What I found inside was "typical" II Morrow, all surface-mount ICs and high-quality circuit boards. It appears to be one of the best assembled radios on the market. But if the SL 40 ever fails, it would be best to send it back to II Morrow. The insides of the SL 40 is no the place to be working with a blowtorch and chisel. I noticed the SL 40 had plenty of inside room and provisions for some more connectors. You can bet II Morrow is going to be stuffing a GPS receiver in this jewel later. Okay, enough fun, time to put the radio back together with all the parts. It went together as easy as it came apart, and it seemed as if I hadn't broken anything (which is unusual for me).

Next step was to hand the SL 40 to my chief installer, Tom Knoll. TK doesn't like anything new, so it was going to be interesting on his opinion of the way the SL 40 wired and integrated with the 2001 GPS. Within three hours, he had the complete harness wired for the SL 40 and 2001, and ready to install in the Cessna. Next, he mounted the SL 40 and 2001 racks and antennas, and ran new coax throughout. Power wiring was run to the circuit breakers, and single point grounding was incorporated. We didn't install any cooling ducts because II Morrow said it wasn't necessary, something about the SL 40 being so efficient that very little heat is generated. The SL 40 uses about one-third of the power of other comms in the same class. Someone in Salem has been doing his homework.

After the installation was complete, we plugged an APU into the aircraft and turned on the switches. My concerns about the SL 40 display being too small were soon gone. I love the display! It's clear and easy to read. Comm radios with LCD displays simply aren't in the same league. I don't usually get excited over something like a comm display, but you would have to see the SL 40 display to understand. It's the best on the market. I personally like it better than the gas discharge displays that the high-end radios use. The little SL 40 has a photocell that dims the display automatically for night use.

Lots of Features

It was finally time to explore the SL 40's bells and whistles. You'd better grab a cup of coffee, because the list of features is long. The display shows both the active and standby frequencies simultaneously, and you can flip-flop the frequencies at the touch of a button, just as with the high-end radios. The large knob controls the MHz and the small one the KHz. The unit covers 760 comm channels from 118.00 to 136.975 MHz. Power output tested out at 8 watts across the entire band, plenty of power for a VHF radio.

Power-on/off, volume and squelch are combined in a single knob. Rotate the knob clockwise to power up the unit, turn it further to increase the volume. Pulling out the knob opens the squelch. The squelch threshold is software-adjustable; no more bench adjustments needed!

Press the "EC" button and 121.50 is automatically loaded into the standby frequency and the "monitor" feature is enabled. What's the "monitor" feature? Are you sitting down, you're gonna love this! As with most radios, the SL 40 normally listens to the active frequency. But if you push the "MON" button, the receiver now monitors the standby frequency, but watches the active frequency in the background. So if there's any activity is on the standby frequency, you'll hear it. But should there be activity on the active frequency, the radio will automatically switch to the active frequency. In short, you can monitor two frequencies at once with this radio. Is that neat or what? A small "m" appears next to the standby frequency display to remind you that monitor mode is enabled, and a small arrow ("<>") will point to whichever frequency you are listening to. Pushing "MON" again turns the monitor feature off.

This is a terrific feature, especially in a single-radio aircraft. You can monitor tower and pick up the ATIS at the same time, for example, without needing a second radio. As far as I'm aware, the SL 40 is the only general aviation panel-mount VHF comm that has this feature.

Ready for another cute feature? Press the "RCL" button and turn the large knob to display the "auto-stack list". Now turn the small knob and you can scan through the last eight frequencies that you saved with the "MEM" button. This lets you call up frequencies that you use a lot without having to dial in all the digits each time.

Another highlight of the SL 40 is its ability to receive the weather band. Just press the "RCL" button, turn the large knob until the display says "WTH", then turn the small knob to the desired weather frequency. Of course you can't transmit on the weather channel, but you sure can receive the local weather. This is a nice feature that has been in handheld transceivers for some time, but I don't know of any other panel-mount radio that covers the weather band.

Yet another feature of the SL 40 is its ability to interface with the 2001 GPS and to obtain frequencies from the 2001's Jeppesen airport database. While this is a neat bell and whistle, I personally found it easier just to read the frequency off the GPS and tune it in manually on the SL 40. I must be old-fashioned.

Having removed the Cessna's old SPA-400 intercom system, we wired the SL 40 to use its built-in intercom. I was really interested on seeing just how well the intercom would work, because most intercoms built into previous comm radios have been poor performers. We had to install a separate switch on the panel so the SL 40's intercom could be turned on. When we flipped the switch, the intercom worked a lot better than I expected. Standby frequency monitoring is disabled when the intercom is functional. An "I" is displayed next to the standby frequency to indicate that the intercom mode is active. Trying out the intercom in the hanger with the engine off, we found that it worked fine and the squelch was set about right.

Another helpful SL 40 feature is stuck-mic protection. We keyed the transmitter, and after about 35 seconds the transmission ceased and "StuckMic" appeared on the SL 40 display. Nice!

So far, the SL 40 seemed to work as expected on the ground with the engine off. But how would it perform in the air?

Flight Test

The floor vacuumed, the APU unplugged, the little Cessna preflighted, and it was time to take her up. We started the little Lycoming and turned on the SL 40 comm, the 2001 GPS, and the transponder (on standby). We tried the weather channel and picked up ATIS before contacting tower. I observed that the weather band and ATIS were at the same listening level, so we didn't have to change the volume level. The reception was very clear...but then again, we were still on the ground.

We gave tower our spiel and got clearance to taxi out. I asked tower how the transmission sounded and they replied "5 by 5". Once in the run up area we tried the intercom function, and once again I was pleased with it. The squelch level was perfect with the engine at idle. Better yet, the alternator whine that used to plague the old SPA-400 was not audible at all. Maybe a well-built radio, shielded wiring, or single-point grounding solved the problem, who knows, but the alternator whine was gone and the owner was delighted.

Tower said "go" so we let the Cessna develop all the power and noise that its little Lyc could manage. I'd forgotten what it was like to fly a Cessna 152: the noise is like being in a jar of bumble bees. At full power we found the intercom wanted to break squelch ever so slightly, but a couple pushes of a button to reprogram the squelch threshold solved the problem. Now the intercom only worked when one of us spoke.

As we reduced power for straight and level, I found the intercom squelch setting was still good. The intercom sounded loud and clear, and worked better than I expected for an intercom built inside the radio. The King KY-96A does have an intercom (well sort of), but it's a "hot mic" system and is poor at best. The SL 40 worked a great deal better. True, it's not a NAT or some other top-end intercom with stereo music and pilot isolation and all that, but it's not bad for the bucks. The SL 40 intercom is limited to two stations and no stereo inputs. If you want to listen to Willie Nelson or need more than two intercom stations, then you need to install a separate intercom system and not use the SL 40's built-in intercom. The system can be easily wired without the intercom.

During the flight we found the comm squelch, receiver and transmitter worked great. During our testing we found that at high engine RPMs and a great distance out, tower would say they heard a lot of back ground noise. Of course the Cessna 152 cockpit has about 97 dB of noise. We found that if we unplugged either the pilot's or copilot's headset, the background noise would go away. It appears both mic audio inputs are connected together so the transmitter sees both mics when either one is keyed. I sure wish II Morrow had installed boom mic isolation inside the SL 40, but it appears that isn't the case. In a quieter aircraft the problem wouldn't have been noticed.

The knobs and pushbuttons worked beautifully. They felt natural to use even in turbulence. The display was a delight to read under all lighting conditions. We tried the frequency storage the SL 40s has and this works along with the down load of frequencies from the 2001GPS, but I found it easier just to manually crank in the frequencies.

I was really pleased with the little SL 40 after we flew with it. I don't like selling a radio that I haven't personally flown with first, I will sell the SL 40 with confidence in the future.

Once on the ground we installed a "boom mic isolator" to cure both mics being on at the same time. We then made another test flight, and sure enough this took care of the background noise problem. Tower commented that we now sounded like an "airliner"! Funny what a $30.00 part will do.


What do I think of the SL 40? I like it! Do I recommend the product? You bet! It works great, everything feels like it should, and it's easy to install. It works on either 14- or 28- volt systems, so it's great for fleet owners who have both. Expect to pay around $1,300.00 for the SL 40 but this is excellent value for product.

This product is the wave of the future. I think II Morrow hit a home run with the SL 40. I'd love to see them come out with a complete radio stack that has the quality of the SL 40, and I fully expect them to do that. And if they ever fire the guy who wrote those great installation and owners manuals, I'd hire him in a heartbeat.