There appears to be an abundance of older, often CB-type Combination SWR-Power Meters showing up at hamfests and even the well-known auction site. You don't need me to tell you that you'll probably get a far better price at a hamfest, however. The following steps chronicle a procedure that is documented elsewhere on the Internet, but I don't know where at the moment.
SWR-POWER METER CONVERSION
Another handy QRP accessory is a QRP-level power meter. It would be even better if it could also measure SWR at QRP levels. If you've been looking at the prices of some of the nice commerically available SWR-Power Meters, you may like this project.
Your first step is to acquire one of the variety of brand name meters as shown below. Although the brand names vary widely, from what I've seen, they are all about the same inside.
We received a break on the price of this one, the seller willing to let it go for $3.00.
Let's say you found one at a reasonable price. Your next step is to order the excellent little SWR-POWER METER PCB Kit from Diz at KitsAndParts.Com. The current price is $8 plus postage. At this point, we have $13 wrapped up in this project and the good news, that is all it is going to cost.
Next, follow the clear instructions on the KitsAndParts website to complete construction of what will be the heart of your converted meter.
Now we open up the bargain meter you acquired and carefully remove the tubing sensors across the back and extraneous small componenets, leaving the case front, two meters, dual-ganged potentiometers and some loose wiring.
We will need to salvage the SO-239s that come hard-soldered to the sensor tubes. In addition, with the U-shaped bracket removed, we now lack hardware to re-secure the SO-239s. While you could raid your junkbox for the appropriately sized nuts, or even buy hardware, a couple of minutes with a hack saw will provide two inside threaded end brackets to secure the SO-239s much as they were before we started.
It is a good idea to remove the paint from the inside of the case where the salvaged spade lugs will go in order to provide a good ground connection.
Following the instructions for your conversion kit, connect the PCB to the two meters and to both the input and output SO-239 connectors.
You may wish to secure the new internal PCB by whatever fashion desired. The following illustrates the use of two segments from a straightened paper clip secured to the two terminal strips carefully removed when first dismantling the meter.
Again following the instructions for the PCB kit, it only takes a few minutes to align or calibrate the two meters by adjusting the PCB pots.
Once satisfied with how the converted meter is operating, just replace the case back and you have a QRP level SWR-Power Meter for a great deal less expense than any commercially available unit.