More SWR meter questions...

So, I have two swr meters, a Workman mod 104 and a MFJ-842.

I connected my TH-D71A to the meters, and tested both the stock duckie and a Diamond SRH77CA.

The MFJ is precalibrated. The 104 is calibrated for the frequency you are testing.

The test showed very different readings for both meters. The MFJ actually looked the most reasonable. The 104 showed the SWR of the Diamond to be over 10:1, and only marginally better for the stock duckie.

Am I doing something wrong? Or are these two meters just junk and I should invest in a better one?

Related question: I assume low reflected power (the MFJ shows forward and reflected power) is good, right?

Thanks all...

You need a ground plane under the antenna to test it. HT antennas rely on the body of the radio to act as a ground plane (or help at least). SWR is calculated based on a ratio of reflected to forward power with some other numbers thrown in.

W5PKY said:

You need a ground plane under the antenna to test it. HT antennas rely on the body of the radio to act as a ground plane (or help at least). SWR is calculated based on a ratio of reflected to forward power with some other numbers thrown in.

Click to expand...

W5PKY - are you saying that you can't check the swr of an HT "local" (attached) antenna because you have removed it from its ground plane?

What about an HT that is using an nmo, mag mount or glass mount antenna?

Thanks,

/greg

External antennas, like NMO, magnet and glass mounts all provide a match due to either their construction or the use of the cars body.

Thanks guys... This was helpful!

You could add a counterpoise ground plane wire (or "rat tail" as they are sometimes called) to the handheld and rubber duck antenna. Here's one way to do it:
https://www.youtube.com/watch?v=szmQmCn1tH4

If you are testing one antenna with one radio at one power setting, then any combination of SWR bridges should show the exact same reading. SWR is a ratio, meaning a fraction that is calculated internally by the device, or the numerator and denominator of which are shown via crossed needles or other techniques so that you can make the calculation. If you are sending the same mount of power out (forward power), the same antenna should always - all other things being equal - reflect the same amount of power (reflected power) back at the radio. This will yield the same ratio every time.

But he was inserting the meter between the "ground plane" and the antenna, which is a no-go. He would have to create a ground plane for that rubber-duck and then put the meter between the radio and the ground plane/antenna combo.

Yes, you are correct, but physics demands that he get the same readings from both meters anyway.

Depends on how the meter's are constructed. Personally, I've never gotten a true reading from a MFJ meter.

I think for the antenna to be tested, just like others said, it needs to be on the radio in in your hand. The other way you could go about testing those antennas is with a field strength meter. Set the meter up at some distance from the handheld, then hold each radio in the same position as you transmit and check the strength. You can only compare two antennas this way, since the readings are relative, but not exact as far as to what the full power output of the radio is.
In general, for an HT, the longer antenna will usually work the best. Buying from a reputable manufacture will insure a quality product.
If you lack the field strength meter, you could use another radio, and put your radio in low power, and have the other radio block the signal a bit so the power is reduced enough to make the readings mean something.