A Low Cost Emergency Personal Locator Beacon (PLB)

For the past two years, I have been hiking with a personal locator beacon in my pack. My ACR 2880 PLB is a 130 gram weight transmitting device that is registered with the Search and Rescue Satellite Aided Tracking System operated by NOAA. For details about this system and how it works, click here:http://www.sarsat.noaa.gov/sys-diag.html

This device differs from the Spot and DeLorme devices in several respects. First, there is no subscription cost. You just purchase the device, register it online with NOAA, and renew every two years online (I put a tickler on my calendar). The battery lasts 5 years. After that, the device has to be returned for refurbishing and recertification. The is a transmit only device designed for one time use. To activate, simply deploy the antenna and press the on button. When activated it sends out two beacons; a five watt distress beacon on 406MHz and a 500mw homing beacon on 121.5 MHz (for the S&R team). The distress beacon is picked up by LEO's as well as geostationary satellites and forwarded to local authorities with personal identification and location information. 

I am primarily a solo hiker, about 90%. I am often bushwhacking in rough terrain. If I am seriously injured or come across an emergency situation, I know that as long as I have a clear view of the sky.  I can quickly summon help, even if I am in a low spot with no cell or repeater coverage.

Fortunately, I have never had to activate the device except for occasional testing to ensure it is still functioning. However, it has provided a lot of peace of mind for me and my XYL, especially when I am activating in unfamiliar and remote areas. 

This system provides world wide coverage and is supported by a number of countries other than US. Check for suitability in your particular country. 

More information on the ACR 2880 can be found here:ACR 2880

EFHW Tri-Band Trapped 17, 20, 30 meter Antenna

Tri-Band SOTA EFHW 

I couldn't do any SOTA activations recently due to work commitments, so I spent some spare time building half a dozen unun's on different cores and comparing them to the Par and Packtenna efhw unun's both on the bench and in my backyard. I came up with a design that works well on my bands of interest, 30, 20, and 17 and doesn't require a capacitor. It uses a FT-82-61 core with a 16:2 winding for a 64:1 impedance transformation. My tests confirmed that a 9:1 unun is adequate to bring down the impedance into a range suitable for use with the Elecraft KX2 internal tuner. One advantage of using a 9:1 with the KX2 is the flexibility of using the antenna as a random wire on other bands where a 64:1 impedance transformation would produce a very low impedance/high current situation for the radio which could result in overheating or inability to find a match. However, I wanted something that I could also attach to a radio without a tuner, such as the LNR MTR3, which requires a low SWR.  I use 10 feet of thin rg174 as a feed/counterpoise, so I didn't want high swr for that reason, as well. My 17 and 20 meter traps are made from the SOTAbeam pico trap parts. Below are the plots of my final design. Plots are with the actual trapped tri-band EFHW. M1, near the top left corner of the chart gives the reading of the frequency under test and the resulting SWR. Green plot is SWR.The SWR's on a recent Dick's Peak activation matched these plots closely. The SARK 110 was indispensable during this project.

        Below: 30m, 20m, 17m field derived plots

Below - Also tested, Clockwise from left: T60-2 (red), FT-114-43 split winding, , NXO-100, FT-114-43 traditional winding.

Final Unun  - FT-82-61 (16:2)

SOTA EFHW UnUn 64:1 transformation

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SPE Expert Amplifier LCD Display Dimmer

I love my SPE 1.3K-FA amplifier, but the LCD panel is too bright and can't be adjusted. I looked around on E-bay and found some 3M film which I cut to size and placed over the display. It looks much better. The cost was $2.49 for a 4x6 sheet. I traced the display window onto a piece of paper, placed the film on top and cut to size.

3M Color Stable 35% VLT Automotive Car Truck Window Tint Film Roll Multi Sz CS35

Antenna Alchemy - End Fed Half Wave Antenna and The Way of the Goat

drawing de DL3TU

2025-04-22 Note: Since this article was published 8 years ago, high power 49:1 UnUns have become widely available commercially, making the EFHW practical for fixed station use. Also, a feature of these antennas that I didn't delve into here is that they are resonant on all multiples of the fundamental design frequency, not just odd multiples like center-fed dipoles. This feature makes them even more attractive, as evidenced by their exploding popularity for both field and fixed-station use. See my 04/2021 blog article "A Simple 4 band EFHW for 40, 20,15, and 10 Meters" for a no-trap mult-band design.

Sota Mountain Goat is an award for accumulating 1000 activator points from mountain summits (see post). At least in Colorado, many of the winter activations are harrowing experiences in cold weather, deep snow, and high wind. Since it's not always practical to "hang around" at the summit the speed to set up and tear down can be critically important. No one wants to invest extreme energy and time climbing a mountain for an activation a descending with nothing to show for it. So, quick deployment and effectiveness are the watchwords for the kit.

When I first started SOTA activations, I looked around at what other, wiser, Goats were using in their kit and tried to copy them. I favored the lighter weight alternatives - no heavy radios, batteries or antennas for me. Aside from the transceiver, and mountaineering gear, the antenna stands out as the most important element of the system. I noticed that most of the Mountain Goats were using the End Fed Half Wave, or EFHW for short. While I had never previously used one, I thought I knew just about everything I needed to know about them. After all, isn't it just another flavor of vertical...? I was wrong. What I discovered shocked and intrigued me, as I think it will you, too.

At first, I was a bit confused about the difference between a random length end-fed, and the EFHW. The terms seem to be used interchangeably. Some of the articles I read had charts that showed lengths to avoid when cutting so-called "random length" wires. Turns out that if you randomly cut your random length wire to one of the "forbidden" lengths, it won't match, even with a tuner, and the SWR losses will be high. So, I initially avoided them. Only later did I learn that those forbidden lengths happen to be the half wavelengths or HW part of the EFHW, and these lengths are where some magic happens.

The Sota Goats don't want to dilly dally at the summit in dicey weather. They often need to set up, work their quota and get down. So, they don't have time for the one thing that we are all told we absolutely need in order to make a vertical work efficiently - radials. They need to extend a pole, string a wire, attach it to the radio and get on the air. The fastest way to do that, and put out a decent signal too, is with the EFHW - an antenna with a forbidden length.

The problem with the EFHW, the reason that it is "forbidden", is that it has an outrageously high feedpoint resistance at resonance - on the order of 3000 ohms. This is not a number that is friendly to any radio and it is outside of the range of typical matching devices. However, it is the high feedpoint resistance that is the secret of its success. Tame it and it will serve you well.

Why is the high impedance that we've been told to avoid actually an advantage? To answer that, let's examine the characteristics of a cousin of the EFHW that we are all familiar with, the quarter wave vertical. The radiation resistance of the quarter wave vertical is about 36 ohms. In a typical installation (4 or so radials) the ground resistance can be substantial - let's say 42 ohms for the sake of illustration. So the antenna presents a decent match to 50 ohm coax of 36 plus 42 ohms = 78 ohms.  The efficiency of this antenna is calculated by dividing the radiation resistance by the radiation resistance plus the ground loss... Rr/(Rr + Rg) = 59%. About 40% of the power is lost in the ground system. The situation gets much worse, however, if only one or two radials are used. The ground loss will rise to perhaps 80 ohms or greater and the efficiency will drop to 25% or so. In other words, the 5 watt QRP radio lugged to the top of the mountain will radiate around 1 watt with one radial attached to a quarter wave vertical.

In a fixed station installation, reducing ground loss is simply a matter of putting down a lot of radials. In the field, this is not so practical. Instead of putting down more radials, one solution is to raise the feedpoint impedance, the reducing the current flow at the base of the vertical and the corresponding ground loss. So, compared to a quater waver vertical with a poor ground systems, the situation improves somewhat with the so-called end fed random wire when it is longer than 1/4 wave. The typical impedance of this antenna is around 500 ohms. The radiation resistance isn't typically any higher than that of a quarter wave vertical but there is less current at the base of the antenna and you can get by with fewer radials. Avoid the "forbidden" lengths (43 feet is a popular length) and it works well with a 9:1 unun. A matching device (tuner) is generally required.

Now let's look at the EFHW. At resonance, the feedpoint resistance is approximately 3500 ohms. Consequently, there's even less current at the base of the antenna, obviating the need for radials. So, with just a short 3 foot counterpoise this antenna should be as efficient as a half wave dipole, making it ideal for quick deployment. Used with traps or jumpers a tuner is not required. SWR of less than 2:1 at resonance is typical with a 64:1 unun (16:2 winding ratio). Refer to the posting for instruction on how to build one.

But there has to be a catch, right? Otherwise, everyone would be using these cheap and simple antennas instead of quarter wave verticals. Well, yes, but most of the limitations just aren't very relevant for QRP in the field. Here are a few of the characteristics and limitations of the EFHW. There aren't any deal breakers on this list for SOTA work. The reason that this antenna isn't more popular in fixed stations has to do more with impedance matching issues than anything else - the popularity of coaxial cable for transmission lines and the lack of good high-efficiency unun's made it impractical, until recently. Broadband unun's with high transformation ratios are still largely the stuff of experimenters - but the experiments have been promising. So, have at it.

• The EFHW can be built for multiple bands by installing traps or jumpers. I use an EFHW built for 40m with a jumper to shorten it for 30 meters. It works well on 40, 20, 10 with the jumper inserted, and on 30, 17/15 with the jumper open. SWR is 1:1 on the half wave frequencies, and matchable with the KX2 internal tuner on the multiples. I have recently built a trapped antenna with good results.  
• Ground losses increase off the resonant frequency and efficiency suffers- cut it precisely for your SOTA freq.
• While the feedpoint resistance of the EFHW is quite high, the radiation resistance is approximately the same as a half wave dipole, 73 ohms (the EFHW is essentially a half wave dipole fed at the end instead of the center). Though radials aren't required, ground proximity and other ohmic losses will adversely affect efficiency, depending on the average height of the wire above ground, and the efficiency of the matching transformer, traps, etc., in the system.
• the impedance of the EFHW is too high for some matching devices (tuners). A 4:1 or 9:1 unun can bring it into range for these tuners. 
• for a low SWR without a matching device, the antenna requires approximately a 49:1 unun impedance transformer (14:2 winding ratio) to match 50 ohm sources. It may be necessary to add a capacitor across the source for a match on the higher bands. I used a 64:1 transformer with success as described in another posting. 
• A counterpoise with an ideal length of .05 wavelengths is recommended. Without a counterpoise, the coax and rig will create the counterpoise. This might be adequate for QRP, but if you can affect the SWR by touching the rig, experiment with the counterpoise. 
• High impedance transformations can be tricky and inefficient. Don't assume your unun is lossless. Care should be taken in the selection of the toroid to avoid losses greater than 3dB. If possible, measure the power into and out of the unun to confirm the efficiency. 
• Be aware of power limitations and do not overdrive ununs to saturation. Ferrite ununs can be permanently damaged by excessive power. In other words, QRP ununs are for QRP!
• Commercial 50:1 unun's in various power ratings are only available from a few suppliers such as QRPGuys, and Pactenna (and high power MyAntenna ununs for base station use). 

In summary, a well designed EFHW is an ideal antenna for QRP situations where a fast deployment is required and center fed dipoles or verticals with radials are not practical. It has been analyzed theoretically and field tested extensively. It is so effective that it has won over many Mountain Goats who started out thinking otherwise. When you absolutely, positively have to set up very quickly and make at least four QSO's after hiking 5 miles to the top of a mountain, the EFHW is a good way to go. 

Summits on the Air - Mountain Goat Award

When Heinrich Hertz proved the existence of electromagnetic waves, they were thought to behave like light (travel in a straight line), thus precluding the possibility of using them for long distance communication (more than 12 miles or so). Marconi thought otherwise. Over one hundred years ago, Marconi defied all expert opinion as well as common sense by proving that electromagnetic waves at certain frequencies will follow the curvature of the earth. He shared the 1909 Nobel prize in physics for this discovery. His technique was to use more and more power (up to 15 kilowatts), longer and longer wavelengths (up to 365 meters), and bigger and bigger antennas (huge wire arrays 100's of feet high) to extend the range of his signals,. On December 12, 1901 he successfully spanned the Atlantic "sparking" the electronics age we live in today.

SOTA activators on summits around the world. continue to stretch the bounds of Marconi's discovery of ionospheric propagation by using flea power, short waves, and small antennas to contact chasers thousands of miles away.

After 150 summit activations, about 3,000 two way contacts and 1000 activator points, I finally became a SOTA Mountain Goat. I just received this beautiful trophy from England which I will proudly display. This challenge entailed round trip signals to New Zealand, Spain, Japan and England from Colorado with 5 watts (the power of a flashlight) and 50 feet of wire! Here I am in contact with England from the 14,276 foot summit of Mt Antero (right photo).

Mt Antero in the distance

"Weightless" Elecraft KX3 or KX2 microphone for SOTA

I operate mostly CW on my SOTA outings, but I always take this light weight mic along since it's built into my earbuds. This is just a standard smartphone ear bud/mic with an adapter purchased on Ebay that allows connection to computer mic/spkr jacks. Turns out that the earphone and mic jacks on the Elecraft KX2 and KX3 are compatible. To transmit, use VOX, or PTT with the XMT button. Note the essential windscreen. This was made with earbud foam hot glued to the mic housing. Keep the glue away from the side with the mic hole. This is a very lightweight microphone solution for the KX2 and KX3. Audio reports are good.

SOTA Spotting with the Yaesu FT-1XDR

The Yaesu FT-1XDR is my go to radio for SOTA activations. I mainly use it for APRS spotting to the SOTA spotting system and it works great. The only problem was that I fumbled around in the cold trying to enter the spot. So, I found a way to store, modify and repost old spots. Here's my boring youtube how-to video, if you really have to know....

I use Google Sheets for my SOTA logging software.  It automatically keeps a cloud backup for me and it easily and quickly provides a CSV file for upload to the SOTA database. Here's my boring youtube video on how to set this up, if you really have to know...

PL-259 Assembly Instructions

Conquering the PL-259

By

Walt Stinson,W0CP

New year's resolutions for hams.... Among the ones I've heard recently is "l will always solder the braid to the PL-259." That got me to thinking about what a hassle it is working with coax and PL-259's (not to mention hardline and N-connectors!).

Well, many years ago after consulting with Mr. Murphy, I made that same resolution. I faithfully followed the instructions for assembly of connectors in the Handbook. I remember using the tip of a nail to unravel the braid and trimming it with scissors.

Two moods would fall over me after a session of soldering 259's: Self-righteousness, for I was truly entering the ranks of the deserving; and klutziness, because about half the time l would have to cut of the end I was working on and start all over again. Sometimes, I'd forget to slip on the fitting cover. Other times  I'd have an intermittent after a couple of years.

Finally, after years of trial and error. I devised a fast and foolproof method of assembling the little buggers. If you follow my prescription, I assure you that you too will enter the ranks of the deserving (of course you will also need an antenna). This method is for RG-8u, but can be modified for other coax. Remember that foam style coax has a lower melting point and is trickier to work with. I recommend sticking with solid dielectric coax for this reason.

Gather up the following tools: (Buy these tools, if you don't have them!!)

Weller D550 240/325 watt soldering gun or Weller SP-120 soldering iron

1" adjustable pipe cutter (Rigid No. 104, available at hardware stores)
Tape measure with sixteenth inch scale
Razor blade style cutting tool

Triple core 60/40 solder, .047" diameter

Black fine point Sharpie pen

Household style pliers

Vise (pana vise)
Grease (dielectric, vaseline, pam, etc)

*********************************************************************************
This method was developed for RG-8u. Remember that foam style coax has a lower melting point and is trickier to work with. I recommend sticking with solid dielectric coax for this reason.
********

Here are the steps: (POST THIS BY YOUR WORKBENCH)

1. Using the razor, cut off 1-1/8" of the outer insulation, exposing the braid.

2. Put the Weller on high and completely tin the braid

3. Measure 5/8" from the end of the coax and mark it with the Sharpie.

4. Using the pipe cutter, scribe the braid at the mark. Then, scribe the braid again 11/16" from the end. These cuts should be to the depth of the dielectric and no further.
5. Now, using the pipe cutter at the scribed point closest to the end, cut through the tinned braid and inner insulation. Be careful not to cut the center conductor. As you get closer to the center conductor, bend the coax a bit to expose the cut so that you don't nick the center conductor. 1/16 inch of the tinned braid should simply fall off at this point due to the second scribe. 

5. Twist off the braid/insulation & tin the exposed center conductor.

6. Slip on the PL-259 sleeve!!!

7. Screw the coax connector onto the coax using the pliers until the center conductor reaches the tip of the fitting. Put a dab of dielectric grease or vaseline on the coax insulation to reduce friction while screwing on the connector. 

8. Secure coax in vise. Heat a hole in the coax fitting. Apply solder through the hole, melting it into braid.

9. Apply solder through all holes. Keep fitting hot but work quickly to avoid melting coax center insulation. Don't flex while coax is hot, allow time to cool in the vise before flexing.

10. Solder the tip of the fitting and check continuity.

Since I have been using this method I have not had one intermittent problem. Moreover, my coax once got caught as I was raising my motorized crank up and the cable just about tore the tri-bander off of the tower! Fortunately, the coax was connected to a balun and a remote switch. The females were ripped out of both of these but my cable was unscathed. This proves another of Murphy's laws - solving one problem simply reveals another.

KN

(PL-259 Assembly Instructions)

Ameritron ALS-600 SPS with switching power supply- In Depth Review

ALS-600 This is the long version of the ALS-600S review. An abbreviated version of this review first appeared in the March 2005 issue of QST. See QST for lab test results. Ameritron ALS-600S with switching power supply - Walt Stinson, W0CP Is measuring "Watts Per Pound" any way to judge amplifiers? If so, the ALS-600S just moved way up in the ranking. The overall weight of the amp and power supply has dropped almost in half, to 22.5 lbs from 44.5 lbs. Wary of back strain from moving amps around the shack, my first reaction upon picking up the amp from UPS was "where’s the other box"? The amp and power supply were shipped in one outer box, with a total shipping weight of just 36 lbs. The ALS-600S is an optional upgrade of the popular ALS-600 (previously reviewed in QST, August, 2001). The only difference between the two models is the power supply. In fact, the new power supply is perfectly compatible with all ALS-600 RF decks and can be purchased separately. If that were all there is to it, this review could end here. However, the ALS-600S is so much lighter than its predecessor that it deserves a fresh look. The ALS-600S utilizes four MRF-150 MOS FET RF output transistors. This device is used by many manufacturers in both transceivers and solid state amplifiers (including the Icom IC-7800 & IC-PW1, Yaesu Quadra, and TenTec Hercules). It is a "tried and true" transistor, originally developed by Motorola and now produced by MA/COMM. It's rated at about 300 watts of power dissipation, so there’s some welcome headroom in this design. The ALS-600 RF deck was designed for Ameritron by Tom Rauch, W8JI, who also had a hand in engineering the noise filtering for the new SPS power supply. ALS-600 vs ALS-500. Though not the subject of this review, Ameritron makes another solid state amplifier, the ALS-500M. This amp utilizes 2SC2879 bipolar output transistors, another popular output transistor that runs with 12 volts. While this amp is undoubtedly used by many hams in the shack, its intended application is mobile. The ALS-600S, with its 50v supply, has about 10dB lower IMD than 12 volt models like the ALS-500M, which means a significantly cleaner signal. Moreover, the ALS-500M requires a hefty 80 amps for full output. Such engineering trade-offs are necessary and appropriate for an amplifier running 12 volts in mobile operations. However, for use in the shack, output transistors that run at a higher voltage are desirable. Solid state FET amplifiers have several obvious advantages. Because the output network is broadband, they do not require tuning. Operation is as easy as setting the correct frequency range on the band switch. Moreover, unlike tubes, the output devices do not deteriorate with use. High voltages are not present, so arcing is not a problem, and the MRF-150 is said to have about the same high-order inter-modulation distortion and momentary overload tolerance as vacuum tube finals. No warm-up operation provides an instant boost in power at the press of a switch. With such advantages, one wonders why solid state amps aren’t more popular. One problem has been the power supply. Apparently, it is easier and less expensive for manufacturers to build a high voltage, low current supply for tubes than to build a high current low voltage switching supply (with low RF noise) for transistors. Ironically, until now, the weight advantage of solid state designs was lost in the conventional power supplies they employ. In fact, solid state amps often have a lower "watts per pound" ratio than their tube counterparts when the weight of the power supply is factored into the equation. Now that Ameritron has addressed that problem, others will certainly follow and the popularity of solid state amps might improve. Tunable tube amplifiers have some clear advantages of their own. The adjustable output networks they employ can be adjusted for SWR changes and buffer the tubes from the "outside world", which in amateur service can be pretty harsh at times. In solid state amps high SWR can cause current and power dissipation to exceed the rating of the output devices. So, RF power FET’s, like those in the ALS-600, require protection from excessive SWR to prevent heat damage. Of course, a manually tuned antenna coupler can always be used with antennas that do not present a nominal load, just as with solid state transceivers. The ALS-600S employs several important protection schemes to improve reliability. At 70 watts of reflected power, the amplifier will fault and automatically switch to standby. At 600 watts output, this will occur when the SWR exceeds 2:1. Reducing the power output to 300 watts, the amplifier will fault at about 3:1 SWR. Toggling the standby switch puts the amplifier back into operation. One way to avoid this faulting is to utilize the ALS-600’s ALC (automatic level control) system to automatically reduce exciter power when the SWR rises. This requires the connection of a shielded audio type cable between the exciter and the amp. The manual does a good job of explaining how to set up the system. The amplifier will also fault if the band selector is set below the operating frequency. A thermal protection circuit will force the amplifier into standby mode when it senses excessive heat. The amp will remain in this mode until the operating temperature drops to a nominal range. Overheating can occur with extended duty cycles that tax the cooling system, or by exceeding the power dissipation rating of the final transistors – a factor of output and SWR. Ten and twelve meter operation requires the addition of a filter board (MOD-10MB), which was obtained from Ameritron for $29.95 and a copy of my license. After removing the top cover, the plug-in board was quickly and easily mounted to the main filter board with four screws. When reinstalling the cover, I was careful to put the vent holes on the same side as the heat sink, as the proper alignment is not otherwise indicated. QSK operation is provided by an external accessory pin-diode switch - model QSK-5 ($349.95). We didn’t test the QSK option. I like to compete from outside the US in DX contests. DXpeditioners have long put a high value on reducing weight, and amplifiers present a problem. My travel amps have included the Yaesu FL-2100, MLA-2500, Alpha 76A, ETO 91B, and ACOM 1000 – heavy beasts all. Years ago, Finnish hams introduced the concept of lightweight DXpedition amps with the FinnFet solid state amps and matching switching supplies they used on several major treks. Available in various power levels, these amps are in the 20 lbs weight class. In late 2001, I decided to find out if the ALS-600 could fill the same niche by mating it with a switching supply and testing it out on a trip to Belize. I acquired a commercial 50 volt switching supply and mated it to the ALS-600 RF deck, just for fun. W1LLU and I used this setup in the 2002 ARRL DX Phone contest, racking up 4,500 QSO’s as V31DJ. Switching power supplies are now standard fare for powering 12v gear, but they haven’t been used much in amplifiers. Aside from the 50 volt requirement of the MRF-150, a big stumbling block is radiated noise. At V31DJ, interference from the commercial switching supply was a problem on some frequencies, especially with the Yagi directly over the shack, and it cost us a few Q’s. This experiment made it quite clear that switching power supplies intended for amateur-use require significant filtering that is absent in general purpose commercial units. It also convinced us of the practicality of mating this amplifier to a switching supply for DX trips - the entire system fit into a case that was previously used to transport the transformer of my previous amplifier, and weighed less. When we returned, I let Ameritron know all about our experiences and encouraged them to look at developing the ALS-600 into a more DXpedition friendly product. They listened! Operating 160-10 meters, multi-single, we unintentionally abused the ALS-600 in just about every possible manner. We ran it into the wrong antenna, put the band switch in the wrong position, and experienced an RF feedback problem that caused excessive drive. We ran it for 48 hours straight with no auxiliary cooling. Nonetheless, I am happy to report that the amp faulted only when it was supposed to. It protected itself from our boneheaded, sleep-deprived band changing maneuvers, and otherwise kept on trucking. One quick toggle of the standby switch was all it ever took to reactivate the amp after a fault. Outside the contest, this amp demonstrated its attributes on the WARC bands, as well. We also gave it a good workout on CW and PSK-31, throttling the power back to 500 watts, as recommended in the manual. Unlike past trips, after a while I found myself not worrying about damaging this amp. It seems quite capable of looking out for itself. The ALS-600SPS power supply provides 50 volts in switch mode at 25 amps maximum (1250 watts) for the MRF-150’s and 14 volts plus and minus at 2 amps for other circuits. There is a separate 12 volt supply for the current surge relay, which also supplies +12 VDC at 200ma maximum to an auxiliary jack on the rear panel of the RF deck. Jumpers allow input voltages between 90-135 VAC and 185-260 VAC. In the USA, the correct setting will almost always be 120 or 240 volts and all my operation was at 120 volts on an ordinary 15 amp household circuit. The SPS interconnects with the RF deck using a heavy duty 6’ cable with Jones connectors. This power supply uses active regulation, as compared to choke regulation in the conventional unit. As a result, the supply voltage is more stable, which keeps the output transistors happy. The supply has a meter on the front panel and, in operation, no sag was apparent in the voltage at full output. I found that the fan noise from the SPS was higher than from the conventional supply or the RF deck. Fortunately, the interconnecting cable is long enough to locate the SPS on the floor. This arrangement frees up some deck space while reducing any annoying fan noise. I am happy to report that the ALS-600SPS power supply is a big improvement over the off the shelf switching power supply I used 3 years ago. The benefits of engaging a talented RF engineer/ham to refine the power supply design are readily apparent when comparing the radiated noise level of the SPS to the commercial unit. I couldn’t hear any noise at all from the SPS on the vertical or Quad located in the yard next to my shack. I then connected a piece of wire to my transceiver’s antenna jack and laid the wire on top of the SPS. I could hear every wall wart in my shack loud and clear, but tuning through the bands and switching the 600S on/off it took me a few minutes to find one barely audible signal from the SPS. Kudos to Ameritron. On the air contacts reported the expected S unit increase in signal strength when the ALS-600 was switched on line. One S unit is nominally 6dB, although the actual calibration varies quite a bit among various receiver models. At 600w output, the calculated increase in strength over a 100 watt transceiver will be about 8 dB. Notably, a 1500w legal limit amplifier will only provide another 4 dB of signal strength – less than an additional S unit. It is important to keep this in mind when considering which amplifier to purchase. I suspect that for many hams, an amplifier in the power class of the ALS-600S provides all the power needed for most situations. Using the 600S at home with my Lightning Bolt quad, which exhibits a very low SWR across five bands (20-17-15-12-10), it was easy to drive to its rated output of 500 watts output on CW with a 100w transceiver. On SSB, I obtained 600 watts output on SSB voice peaks. The theoretical output limit of the amp is about 700 watts, but it’s a good idea to stay 100 watts below that in order to keep the distortion products at a low level. Adjacent operators will thank you. Operation on RTTY is possible, but it’s advisable to keep the power below 300 watts unless an auxiliary fan is utilized (Papst 4530Z, part # 410-3140, $43). With the fan, the rating goes up to 500 watts (with a duty cycle of 2 min on, 1 off). The standard power supply has a front panel RTTY switch to reduce the high voltage to 30 volts and the maximum output to about 275 watts. The SPS lacks this feature, so it’s necessary to reduce the drive power when using digital modes. It is bad practice to overdrive any amplifier, particularly solid state units. They tend to distort more severely than tubes when overdriven. Ameritron uses a 35 ohm, 50 watt, snap-in attenuating resistor to match the input sensitivity of the 600S to the output of a typical transceiver (older versions used a 45 ohm resistor). This also serves to bring the amp into compliance with FCC regulations that limit the drive sensitivity of amplifiers capable of transmitting on 10/12 meters. The value of this resistor assumes a 100 watt output exciter and yours might be higher or lower. If higher, you’ll have ensure that you throttle back the drive. Over time, I came to greatly appreciate the size, weight, reliability and simplicity of this amplifier. My XYL, K0ZV, also enjoyed using the amplifier, especially when chasing DX. Still, there are a few improvements I would like to see. Automatic band switching capability would leverage the convenience of "no-tuneup" and add greatly to the appeal of this amplifier, as would a built-in QSK option. I’d definitely like the SPS to be smaller. Both cabinets have side vent holes, but the SPS is slightly longer and narrower than the RF deck and stacking is awkward. The circuit board on the SPS has unusually wide component spacing when compared to its commercial counterpart and occupies about the same desk space as the old style power supply. There appears to be enough room in both the RF deck and SPS to shave another 10-20% off the dimensions, plus the corresponding weight. The SPS meter is a nice touch but it seems unnecessary and could be sacrificed in the interest of reducing size and weight. While some weight improvement could also be obtained by combining the two units into one chassis, getting the power supply off the desk saves space and reduces fan noise. I’d welcome an integrated unit, if the fan noise was reduced along with the combined size. The lamps in the RF deck and SPS meters are overly bright and mine burned out after a couple of years. I replaced them with super reliable LED’s. Now that white ones are available, LED’s should be standard for meter illumination. The owner’s manual, while including comprehensive schematics and operating instructions, lacks a concise specifications page. It includes a brief addendum for the SPS (no schematics), but otherwise has not been updated for the 600S. In designing any amplifier there are engineering trade-offs. In the real world there is no "perfect" amplifier. In the past, the desire to achieve high performance and low price has necessitated trade-offs of space and weight. As a teenage ham, I owned a Heath Apache that weighed 100 pounds. I doubt that a 120 watt, 100 pound transmitter could sell today. A steady improvement in technology through the ensuing years has permitted size to shrink and weight to drop. For the most part, these advances have not been as evident in amplifiers as they have been in transceivers. For the sake of our backs, it’s time for that to change. Even tube amps can now be designed with a switching supply. Hopefully, we’ll see more examples in the future. There’s nothing fun about lugging around a 60 lbs amplifier – or paying excess baggage charges. But now, fellow Contesters and DXpeditioners, the ALS-600S makes it possible to pack a transceiver and 600 watt amp that together weigh less than 30 pounds. (c) Copyright 2004 by Walton Stinson. All rights reserved.