Start at the bottom, not at the top :)

[KD3Y]

I had a nice day today.  Weather has been nice in Coastal Carolina, summer time is coming.

So I re-learned a lesson I should've remembered from the past..."Start at the bottom, not at the top."

I cranked up the rig this morning to do me a few contacts, and WTH?  The SWR was at least three.  That's abnormal for my rig.  I'm usually in the 1.3 ~ 1.5 range. <panic sets in>.  Now in our subtropical climate here on the coast, we get rain about daily in the evenings.  We've had some weather over the last week or so with high winds.  So first thing pops in my mind is, "Dangit.  my dipole has stretched by the wind or water has gotten into my coax."  So I trudge out to the pine trees in the backyard, lower the dipole, check all the connections, open the cover, see the connections are all dry and still connected, and run it back up the tree.  I go back inside, fire it up, sure enough, still SWR of 3. Not much signal seems to be getting out.  So I head back to the pine trees with my MFJ, run the dipole back down, put the meter on it, SWR 1.3.  <musta jiggled something.  It works now>.  Run the dipole back up the tree and go back inside.  Still SWR of 3.  "OK.  Them dang squirrels musta chewed my coax again"
So I disconnect my rig at the antenna socket and put the MFJ on it to test the coax and all.   1.3 SWR.  So with the radio plugged in the SWR in 3 and from the PL it's awesome.  Must be the danged radio.   <more panic sets it>.  Now I'm sitting there wondering how much a new HF rig is gonna cost me.  $$$$

As I'm sitting there at my desk grieving over my situation I happen to look up at my rig and notice...my protegee was over the other day, was impressed by my morse key, and naturally I had to show off a bit so I flipped it over to CW mode and did some dits and dots for him.  And I left the mode on CW rather than switching it back to SSB after we were done.  <light comes on it head>.  I "mash" the SSB button, key the mic, say a few words, and the SWR meter jumps all the way up to 1.3-ish.

After about three hours of work in the backyard in the sun I learned what the problem was...  An "ID-ten-T" error.
The old adage I've realized over my 50 years proved true once again, "If you want to learn, be a teacher".  Only this time the student and the teacher was one in the same.

So the buttons on my rig are all in the right positions now, my SWR is back down to 1.3-ish, and I'm a tad smarter.

Start at the bottom, not at the top.
Anthony, KD3Y

[K3MRI]

Such a good lesson!! And a nice chuckle to start my day.

[KD3Y]

Good morning Jim.  Time for another one of them educational topics like you put up like last time.
I was wondering why the mode affects the SWR so I googled it.  Here's what I found posted elsewhere one the Interwebs:

Q: SWR: Does modulation type matter?

Answer #1:  SWR requires power to get a true reading. So SSB on its own with no noise has no real power, its just a quiet unreadable carrier. If you whistle into the SSB unit, you will see a measure.  If you use the FM which has full power output due to the modulation. It would do the job, as long as you are on the same freq. Many times on HF rigs people will use CW tone at low power to swr/tune. Or an FM/AM Mode works too if your rig only has that! SSB, FM, AM, CW, etc. All output at same frequency, its just HOW they output their power and such. so SWR can be measured by any and used by any if its the same frequency.

Answer #2: Yes, the swr will be the same regardless of the mode you use. Some people whistle into the mic to test swr in ssb.

 

Make me understand, if the above answers are correct, why I have a 3 SWR on CW mode and a 1.2 SWR on SSB mode.  Shouldn't my SWR measure the same if I'm using the same meter on the same radio? 


Anthony, KD3Y

[K3MRI]

When comparing Continuous Wave (CW) and Single Sideband (SSB) signals, the primary difference comes from the nature of the signals themselves. Note that I am assuming here that you transmitted on CW and SSB at the same power level!

CW is a simple on/off keying of a carrier wave. It's either transmitting at full power, or it's not transmitting at all - but at some point it is transmitting at full power!! As such, it's fairly easy to tune your antenna and transmission line for a good match at the single frequency of the CW signal but, again, it is at full power.

SSB, on the other hand, is a more complex signal. It's derived from an Amplitude Modulated (AM) signal by removing (suppressing) one of the sidebands and the carrier. The result is a signal that varies in both frequency and amplitude, and that can cause a varying load on the antenna and transmission line, which in turn can cause the SWR to change. If you were to broadcast/yell a continuous high volume into the keyed mike, you would see that your SWR would go up. If you just key up, you're sending very low amplitude.

In summary, CW signals have a constant frequency and amplitude which makes it easier to maintain a low SWR compared to a loud SSB signal, while SSB signals have varying frequency and amplitude which can lead to a lower or higher and more variable SWR.

Hope this helps 😉

Jim

[WA3LTJ]

The SWR should be the same if you are operating on the same frequency. If you tested CW on the low end of the band, then operated SSB on the high end of the band, you might get very different SWR readings.  I always measure the SWR across the entire band in 50 KHz steps. I typically use 5 to 10 W of power and only key the transmitter long enough to make a clean measurement. When operating portable, I rarely carry a CW key. There are two solutions to that limitation. You can simply wire a switch to a phone plug and use it like a key to make the measurement. The other solution I use is a bit more complicated. My Yaesu has very different settings for AM, FM, CW and SSB. I set up the AM for: 5 to 10 W, mic level set to zero, mike input on the back of the rig (where there is no mic). This assures me a carrier with no voice when I hit the PTT switch on my mic. 

The readings with the rig should be very close to readings with a SWR analyzer. I often bring the analyzer unless I am doing backpack POTA (Parks On The Air). The analyzer is faster and easier, and mine does a plot for me. Another benefit of the analyzer is that it gives you readings outside of the band. If the lowest SWR is outside of the band, then it would be very useful to adjust the length of the antenna (see next paragraph).

The plot should have a minimum point somewhere in the band. The SWR may slope up more quickly at the higher frequencies. If the SWR is much over 3:1 where you operate the most, it is probably best to adjust the length of the antenna. The plot is useful to decide whether to add or remove length. If your favorite frequency is below the lowest SWR point of the plot, add some wire. The Antenna Handbook and some other sources suggest how much to add or subtract on each band. 

[WA3LTJ]

I am not thrilled with K3MRI's explanation and I cannot explain a lower SWR reading with CW except for the possible transmit frequency difference. 

For people who are over-the-top technical, I will note that certain high-Q antennas, like a small loop antenna, can give a lower SWR for CW than SSB (or AM or FM). This is a special case where the loop diameter is very small relative to the carrier frequency. The passband characteristics of the resonant loop may be smaller than the ~3 KHz of the SSB signal. The SSB signal thus injects energy beyond the low SWR region of the resonant loop. Thus, some of the signal will be attenuated (reflected back). Note that a high-Q loop will tend to reduce harmonics from a transmitter. This can be helpful when using a home-made CW QRP rig with only marginal low pass filtering, although I have never see a careful evaluation of this benefit.  

[K3MRI]

6 hours ago, WA3LTJ said:

I am not thrilled with K3MRI's explanation and I cannot explain a lower SWR reading with CW except for the possible transmit frequency difference. 

For people who are over-the-top technical, I will note that certain high-Q antennas, like a small loop antenna, can give a lower SWR for CW than SSB (or AM or FM). This is a special case where the loop diameter is very small relative to the carrier frequency. The passband characteristics of the resonant loop may be smaller than the ~3 KHz of the SSB signal. The SSB signal thus injects energy beyond the low SWR region of the resonant loop. Thus, some of the signal will be attenuated (reflected back). Note that a high-Q loop will tend to reduce harmonics from a transmitter. This can be helpful when using a home-made CW QRP rig with only marginal low pass filtering, although I have never see a careful evaluation of this benefit.  

And I am thrilled that WA3TLJ has chimed in because if anyone can put me back in my place, it is he! 😅😎