Reception OK, SWR too high to transmit - will external tuner help?

[TexTAC]

I have a RadioWavz DX40 off center fed dipole antenna and a Yaesu 991A transceiver. The internal tuner on the 991A can tune it on the 40m, 20m, and 10 meter bands. I’ve made DX contacts on all three bands.

The internal tuner on the 991A won’t tune the antenna to an acceptable SWR on the other bands (and I wasn’t really expecting it to when I bought the antenna). The radio says SWR is infinity on those bands. However, I do get pretty good reception on the 80m and 60m bands even though the SWR is not at an acceptable level for the internal tuner.

My question is will an external tuner be able to tune this antenna on 80m and 60m so that I could successfully transmit on these bands? I guess I don’t understand why I can receive so well on bands with very poor SWR. Also, what are the specs I should be looking at for an external tuner. My radio is 100w and I don’t have current plans for an amp (although I may in the future).

 

[alcahuete]

Maybe, maybe not. It just depends on the tuner. The problem with any tuner is that you are still running an out-of-tune and inefficient antenna. The tuner just makes it look like a resonant antenna to the radio, so that the radio will transmit at full power. A tuner doesn't magically make the antenna efficient. I can tune my tri-band (20, 15, 10) beam antenna to work on 80 meters. Doesn't work more than a few states away.

The SWR really doesn't matter as far as receive is concerned. I can pick up HF (quite well) with an old pair of rabbit ears TV antenna. In fact, one of my portable shortwave radios has about a 24 inch telescoping antenna. I can hear signals from all over the world. Now if I tried to transmit on that antenna?

So at the end of the day, yes, a good tuner will probably be able to tune that antenna to work on 80m and 60m. It isn't going to work well, but it will work. You really need a larger antenna.

 

[TexTAC]

If I understand correctly, the tuner will enable me to transmit at 100 watts safely without destroying my radio, but the actual power the antenna puts out will be a very small percentage of what is transmitted? A lot of the signal will still be reflected back towards the radio, but the tuner will render the reflected signal safe before it gets to the radio?

My only option at this point in the hobby for a larger antenna is a longer wire antenna. I could possibly do an 80m dipole, but that would have to zig zag all around my property. I was hoping I could make this 40m OCF dipole work on 80m. It works quite well on 40m and 20m (and 10m when the band is open).

Thank you for answering!

 

[alcahuete]

You're welcome! Yes, everything you said is accurate. The tuner tricks your radio into thinking it is transmitting into a balanced load, and thus allows the radio to transmit the full 100w in a safe manner. Perfectly safe for your radio.

You can certainly give it a try. Any really good tuner shouldn't have a problem tuning it on 80m. Just have realistic expectations going in. You probably aren't going to work worldwide DX on it, but within a couple thousand miles, it will probably work just fine.

 

[prcguy]

I have a remote HF station that uses a 40-10m EFHW antenna and occasionally force feed it on 80m. I have an LDG IT100 tuner and its able to get a good enough match so the radio is happy but the radiated power is very low since its a 1/4 wave on 80m and fairly low impedance being fed from a very high impedance transformer.

An OCFD will be a little different being a 1/4 wave on 80m but tapped off center and fed with a 4:1. Some brands of external tuner should be able to get a good match but I suspect the radiated power will be lower than my end fed. When conditions are good on 80 a little bit of radiated power can go a long way so its worth a try. It should work good enough to get from my radio in Richardson to TexTAC in Plano, or about 3 miles.

 

[TexTAC]

If I do get an external tuner, I may want to give that 3 mile transmission on 80m a try.

 

[musiclistener]

Look into an inverted V antenna. Alpha Delta fan dipole. My internal tuner on my Kenwood 570SG tunes them all. Each band has a dedicated wire.
DX Engineering is where I got mine. It's been up and working for 15 years. Hope this helps.

 

[paulears]

The old joke about transmitting on a wet bit of string really does apply. You just need to swap your thinking around. VSWR is indeed a ratio of energy going out and not back, but the destroying your radio thing is perhaps a bit of a stretch. Most radios have sensing which throttles the output back for poor loads. If Yaesu or Icom made a radio easily destroyed by bad VSWR they's never sell any! Sure - it's bad form, but the stories of death and destruction are a bit over-rated. A dummy load has a great VSWR but is rubbish at radiating, and that is the key here - making a random length of metal in the sky get the signal out in a useful direction with as high efficiency as you can manage. It's also reciprocal - a rubbish transmit antenna is also a rubbish receive one! Year back, a friend had a disused railway line at the end of his garden, and he discovered the thing had been track circuited and the rail was insulated from ground. He attached a cable, and tuned it up with an ATU. He used the old top band allocation for a few years with amazing results till they lifted the line!

 

[popnokick]

The internal tuners on many transceivers typically are less tolerant of SWR mismatch than an external tuner would be. I know this from firsthand experience with a fellow ham's FT-991A. He switched to an external tuner (LDG) and was able to tune a vertical on his RV on 80M that was out of range for the internal tuner on the Yaesu. However, it was a very tiny slice of 80M where it tuned, and at reduced power as was noted in this thread. The real answer as you noted is to either get the RadioWavz DX80 longer antenna or perhaps an EFHW for 10-80M. The DX80 will also do 6 Meters... the EFHW will not. And switching to an 80M dipole is not going to give you the multi-band capability you currently enjoy with the DX40 (or DX80 should you get one).

 

[tweiss3]

Look at the specifics of each tuner. Most internal tuners can correct 3:1 SWR, and most of the external tuners will correct 10:1 or less. Of your SWR is greater than that, you not be able to find a match. If you have one, hook up a nanoVNA and see exactly what the SWR is on the 80m band, look at the smith chart which will show and ohm and capacitance reading.

Keep in mind, 80m is a very wide band for a wire antenna. My antenna has a match on the CW/digital portion of 80, but the voice portion is a terrible match, so your bandwidth will likely be even more narrow.

Lastly, be mindful of your intended power and duty cycle. Most 100w tuners are not rated for a high duty cycle, especially digital, at that 100 watts. You can fry a tuner pretty quickly if you exceed it's specifications.

 

[prcguy]

If TexTAC can wait until late December I'll be in his area and can bring a 100w LDG tuner that will tune a 10:1 mismatch and also an 80m OCFD or 80m EFHW for testing that coverers all bands including WARC 80 through 10m usually without a tuner. These 80m antennas are 133ft long but can be bent up some to fit.