The Diamond SX-400 is a nice desktop power and SWR meter that covers the 140-525MHz range. I use this meter to test all of my handheld radios to see how much power they really put out. Read on to learn more!
I have been using Diamond products for about as long as I have been into amateur radio, probably going on thirty years. Their power and SWR meters have been on my desk for about as long, although his particular Diamond SX-400 has only been with me a few months (lightning is a terrible thing).
The Diamond SX-400 is a relatively small SWR power meter at about 6″x3″x4″ meant to sit on your desk and plugin between your radio and antenna. It allows you to measure forward power, reflected power, and to measure SWR in a power range from about .1watt to 200watts.
One of the things I like is that the Diamond SX-400 features fairly large flip switches you use to turn the unit on and select the function you want to use. The area where I use my radio tends to be a shadowy area and making the controls large and easy to use really makes a difference. All of those controls also feel really well done, there isn’t anything that feels cheap or like it will break.
Speaking of my shadowy ham shack area, the Diamond SX-400 has a nice lit meter area so you can see it clearly anywhere from broad daylight to pitch black of night. My only complaint here is that the light is not adjustable so if you really are in a pitch-black room the backlight is pretty bright.
Next up is the accuracy of the Diamond SX-400 and since I am not a professional engineer, I really have no way to test and make sure it is that accurate, so I will tell you what I know. One thing that makes me think it is fairly accurate is that it is consistent. By that I mean if I test the same radio on the same frequency with the same antenna several times I get the same results. Even when I go back and test the same setup months later my results wind up being the same. I have used a lot of cheap power meters that give you a wildly different reading every time you use them, that is not the case with my Diamond SX-400.
Another thing that leads me to believe the Diamond SX-400 is accurate is that the numbers make sense. When I use a cheap eBay power meter I see things like an HT rated at 5w putting out 18w, but when I put that same HT on this meter I get something like 4w.
Lastly, I have seen comparisons of the same equipment measured with a Bird Watt Meter and the Diamond SX-400 and the show as extremely close, more than close enough to be considered accurate unless you literally are a scientist.
On the back, the Diamond SX-400 has three connections, two UHF for the input and output, and a power connection shown in the bottom left of the image above. I took the power cable supplied with the Diamond SX-400 which had bare wire ends and put Anderson Power Pole connections on them to use with my power supplies. I also bought some two-foot adapter cables which have male UHF connections on one end and then one with a male SMA and one with a female SMA so I can attach virtually any handheld radio to one side and its antenna to the other side of the Diamond SX-400.
Unlike some other units, the Diamond SX-400 requires external power to operate. Some units only require power for the backlight, this is not one of them. No power means it does not work at all. When I first hear that I was a little disappointed but, to be honest, I have a ton of power available pretty much everywhere in my office so putting some APP connectors on it and plugging it in was no big deal.
The Diamond SX-400 manual is basic but more than suitable considering there is not a lot to know. The only thing I really used it for was to figure out how to calibrate the unit for measuring SWR and that took about a minute flat.
The Diamond SX-400 price is right around $130 currently and in my opinion is well worth it. Yes, you can get a lot cheaper power meters off of eBay or amazon but in many cases, you get exactly what you pay for. I bought one of the really popular GY561 units for about $40 I think and although a nifty little toy, it is just that, a toy. Readings are wildly inaccurate, almost to the point of being comical at times. When compared to my Diamond SX-400 there is just no contest.
I really like my Diamond SWR power meter and if you need something for the 2m-70cm range that is simple, economical, and accurate like this Diamond SX-400 then I highly recommend it. If you need something to do HF as well, the Diamond SX-600 is about $50 more and goes to 1MHz.