This dummy load is small enough to carry in my tool case when doing HF transmitter evaluation on site. The VHF or UHF operation is a plus. The C is significantly better for that than the B. The C restricts airflow, and might not handle long key down operation as well as the B version. There is a fix for that, shown below. Quality is what you would expect for the price.

I never cease to be amazed when people give bad reviews to something so useful at an affordable price. I observed no blemishes in the paint. Maybe they upgraded the paint process from the A version. Not lab grade, but perfect for quick checks in the field. There are some complaints on eham about hearing signals due to poor shielding. I did not see this problem, but I am obsessive about good patch cables in my shack and on my test bench. Don't buy cheap badly crimped cables. I do not want to waste my bench time trouble shooting cables. That having been said, I contacted a local friend back in 1960 as a Johnny Novice using 60 watts and a light bulb dummy load. Compared to my Gotham Vertical with no ground wires, I was much weaker than normal, but still readable.

I acquired one of these 260 dummy loads cheap and broke at a ham swap meet. The first one, a 260-B, had mounting screws for the power resistor which were loose and rattling around in the case, but the resistor element tested good when the contact surfaces were cleaned and reassembled. I bent the mounting clips to clamp it better, gently cleaned the contact ends with a rag and some alcohol, reassembled it, and voila! The resistance was exactly 50 ohms. Nice! I usually leave it attached to the unused Antenna 2 port (for six meters) on my Yaesu FT-950. I disconnect the antennas at all times when off the air for lightning protection. This prevents me from keying up into an open circuit if I do something stupid when I am in a hurry. The power of the rig is set to 25 watts for FM, and this termination is good enough to take that. If I need it for other uses, I disconnect it from the stub of coax and it's ready to go.

I pick these up whenever I can, as "shack warming" gifts for new hams to use on their 100 watt class transceivers. They often go for $20 if they test good, or less if there are obvious problems. They are also small enough to carry with a compact power meter to the swap meets. If you want to evaluate a rig at a swap meet, and can get 12 Volts DC from a car battery, you may have enough to confirm power output before you buy.

Comparison shopping: Used Bird dummy loads are available for around $50 - $75. They are bulky and heavy, so these live under your desk. They do have a handle, but they are portable only in the military sense. Not the sort of thing you put in a briefcase sized tool kit. If you look at the big Bird dummy loads at the swap meets, check the resistance first. Then unscrew the cap to the filler for the fluid and make sure it is not empty, and there is no evidence of corrosion; there is some room left for expansion as you heat it up, so do not add fluid unless it really needs it. This is fancy unobtainium NON PCB transformer oil, and you can get it, but you have to know somebody. The last thing to check on a Bird is the connector, often a type N. Be aware there is a slightly larger N connector used in the broadcast industry that will not fit a standard N coax cable or adapter. Carry a standard N connector in your test gear bag or pocket to check the size before you buy. The standard N to SO-239 adapters are cheap and widely available. I was lucky enough to have in my junk box the correct SO-239 connector and plate for the Bird I bought. The boss at the 2 way radio shop I worked at had me convert the Bird Wattmeter to N connectors, so the SO-239s were discarded. I never throw anything away; it was just a matter of digging through bins in the garage.

What are the differences in specifications for the MFJ 260-B and MFJ 260-C? The B works up to 2 meters. The C is good to UHF. How they get the performance above 10 Meters is done with a trick. I will show you both, in the photo section below.

SPECIFICATIONS (MFJ 260C):

• DRY, AIR COOLED, NO MESSY OIL
• 300 W FOR 30 SEC WITH 2 MIN COOL DOWN
• 25 W CONTINUOUS
• MFJ 260-B: FREQUENCY 1 TO 150 MHZ
• MFJ 260-C: FREQUENCY 1 TO 650 MHZ
• SWR 1.3:1 MAX

The specs and power derating curve is printed right on the case. I would never use this dummy load at 300 watts, but it is adequate for short tests at 100 watts. Click on any picture to enlarge. You can see the differences between the two models in the specs. Also, the 260-C is gray instead of black.

   

The simple problem on the MFJ 260-B I bought was a loose screw, which grounds the end of the resistor. Almost everything I get at a swap meet has some problems. Often they are simple. I usually carry a test meter and some simple tools when shopping. This one rattled, and measured open. Unless it was dropped, and the resistor element shattered, I speculated the problem was hardware. The price was cheap enough I could take the risk. The 2 meter performance is due to a trick, a 12 pF 1KV capacitor across the input. If this resistor is damaged and you have to replace it, keep the lead length as shown.

       

The MFJ 260-C I bought tested about 55 ohms (accounting for the test leads). It was like new, and in the box, so I paid more for it. No rattles either. MFJ did significant product improvement over the span of three models. When I got it home, I saw how it got to 70 CM. A metal dog house was place over the resistor to keep the impedance at RF frequencies close to 50 ohms. Fewer holes were in the bottom, which restricted air flow. I decided that needed some help, to keep the power rating at the specified curve. These resistors drift in value when over heated. It would be better to take out some insurance. I drilled two more holes, at the ends, using the same spacing. I enlarged them all to allow more convection air flow. The inside of the case and the dog house were painted flat black to help radiational cooling. I used masking tape to avoid getting paint on the outside of the case and the mounting ears of the dog house. The dog house must make good contact with ground. Heat escapes by convection (air flow), radiation (flat black paint helps), and conduction to the case. Observe the 2 minute long rest time in the specs when at higher powers. There is no capacitor needed in the MFJ 260-C. The resistance was a bit high, 55 ohms, but the SWR met spec. I had worried it had been stressed by applying 100 watts for too long a period with no cool down time. The resistor tolerance stamped on the element is 10%, so it probably just came that way from the factory. I swapped the elements between the two dummy loads, because the MFJ 260-C had flatter frequency performance. The more versatile and now more accurate MFJ 260-C could be used on the test bench, and the other one could work as idiot protection for the FT-950.

To keep the air flowing, a small fan from a junked computer operated from a wall wart could be installed over the vent holes in the top cover. Drake uses that to boost the power level of their dummy load reviewed elsewhere on this page. I would still consider the fan modification just protection for the resistor from the ambitious power specs of the rating curves.

           

I hope you found this web page helpful for shopping for equipment or repairing something that got damaged. I also try to explain "why" something works the way it does, so that you can become more proficient in the technical aspects of amateur radio. I recently had a discussion with a new ham about the Bird dummy loads; he thought that they were only good for UHF and would not work on HF. If you can measure the resistance with a meter, it is good to DC. Likewise, the MFJ spec is misleading, since they state the frequency span as 1 MHz to something. These dummy loads will work just fine below 1 MHz for your 2200 and 600 meter band testing. They are OK for audio too, but not much audio gear is 50 ohm. You can load test a 13 VDC power supply, but it will only draw about 0.26 amps. It really helps to understand the theory, not just memorize the answers to test questions. Invest some time experimenting to add to your enjoyment of ham radio. Its worth the effort!