How "bad" is bad SWR and still transmit?

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wbswetnam

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A newbie ham here... I recently made a dual-band dipole antenna following this design I saw on Youtube (Ham Radio 2m/70cm Vertical Dipole Antenna - YouTube) and I accidentally cut the elements a bit too short. I used a MFJ-269 to test the SWR and I get the best SWR (1.1) at about 151.000 instead of 147.000 which is what I was aiming for. At about 147.000 I get an SWR of about 1.8, and on 70cm I get an SWR of about 1.8 at 446.000. It has the best UHF SWR (about 1.3) at about 453.000, which these would be great values for a scanner antenna but I was wanting a ham antenna! Anyway, the values I was shooting for (147.000 and 446.000) still give me an SWR below 2.0 so is it still safe for me to use it with a handheld 5 watt transceiver? I have a Yaesu FT-60. If it is a bad idea to try to use it for 2m/70cm amateur radio, then I guess I can use it as a homemade outdoor scanner antenna. Thx and 73s! KF5YOF
 

wesm1957

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I made the same antenna that I put up for a second antenna for my shack. I have a HT connected to this antenna. I made mine with 1/8 inch brass rod. You could silver solder small tubing to your elements if they are too short to bring them back to the correct length. Just an idea.

73's

Wes
 

N5TWB

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While SWR is a good indicator, it is not necessarily the be-all and end-all in the effectiveness of your system. I don't see any reason to back off from using it at those measurements, especially on the UHF band as you'll be transmitting in the top half (446-449.995) so you're closer to your ideal SWR point.
 

K7MEM

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In the manual for the FT60R it says:

"If using an external antenna for transmission, ensure that the SWR presented to the transceiver is 1.5:1 or lower, to avoid excessive feed line loss."

That is true, but if your feed line is short feed line, loss shouldn't be a problem. Generally, any SWR below 2:1 is usable without damaging your transceiver. Most new transceivers have fold back circuitry that starts reducing the output power if the SWR is too high. But I didn't find any specification for that in the FT60R manual.

Years ago, while I was in Germany, I operated 15 and 40 Meters CW a lot. My antenna was crude and gave me a 10:1 SWR. However, I was transmitting from the second floor, using a transmitter with tubes, and was only 10 feet from the antenna feed point. So I ignored the SWR and had a great time making contacts.

So "How bad is bad" depends on your particular situation.
 

wbswetnam

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OK thanks, maybe I can get away with using it for both a scanner antenna AND a 2m/70cm ham antenna. I'll give both a try. Actually I tried it as a scanner antenna already today to see what kind of reception I get using it with my RS Pro-96 scanner, and I get much improved reception over the stock antenna. I have it at the end of a piece of PVC pipe about 15 feet off the ground.
 

dksac2

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Your radio will either roll over the power until there is little to no power transmitted or you'll blow up your radio. Try to stay under 2.5 to 1 at the very most, under 2 to 1 is best.

John KF7VXA
 

wbswetnam

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This past weekend I was at a local hamfest, and I bought a nice 2m J-pole antenna another ham was selling. I put it up on the house and I measured the SWR for 2m.... no more than 1.5:1 SWR across the band, and 1.2:1 right at 147.000 MHz. I connected my Yaesu FT60 and I easily hit a repeater 20 miles east of me and another one 25 miles to the south. Very nice! Of course I also tested it out with the Home Patrol 1, and I was picking up counties I had never heard before despite the antenna not being cut for 155 MHz frequencies.
 

ab3a

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A better way to look at SWR of an antenna is if you convert it to "return-loss". The return loss of a 3:1 SWR is 6 dB. In other words, 1/4 of your power will be reflected back to the radio. But your signal power less a six dB return loss is minimal lost.

In other words, the biggest concern you should have is matching your radio so that it doesn't turn down your power.

That said, if you're running on UHF and you're using a long coaxial cable, you should pay attention to VSWR at the transmitter end. Supposing you lose about 4 dB over the length of the cable (That's pretty typical), even if you had a completely shorted connector at the far end, you'd still read an SWR of 2.3:1 at the transmitter end.

So SWR indications are not a good indicator of antenna health unless you account for the feedline losses.

For a complete discussion of this issue and more see SWR, Return Loss, and Reflection Coefficient
 

CommJunkie

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While SWR is a good indicator, it is not necessarily the be-all and end-all in the effectiveness of your system. I don't see any reason to back off from using it at those measurements, especially on the UHF band as you'll be transmitting in the top half (446-449.995) so you're closer to your ideal SWR point.
Not always. Around me, UHF repeaters can go either way. The one I use the most uses an input tx freq 5mhz below the rx freq.
 

LtDoc

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How bad is "bad SWR"? Good question and it's always variable. It depends on what you expect and what's practical. It's really only 'bad' when it causes damage. SWR is a VERY misunderstood thingy. It deals with impedance matching between devices and the efficient transfer of power from one place to another, that's all. When dealing with antennas there are always two things to consider/adjust. Impedance matching (SWR) and resonance. If you only deal with SWR when tuning an antenna you will seldom ever end up with a system that radiates well. It may be 'matched' to a knat's eyebrow, but still won't be the best you could have. You can't get any better SWR than with a dummy load, right? But dummy loads make terrible antennas, they don't have the ability to form a radiation pattern worth a hoot, or do that radiating. Does an antenna always have to be resonant? Nope, sure doesn't, but resonance does make a big difference. The typical way of adjusting for SWR is also the worst way of adjusting for resonance (length adjustments). But that's the simplest way! Yep, but how often is the simplest way the 'best' way??
- 'Doc

Resonance is defined as the absence of reactance. That's 'good' because reactance doesn't contribute to radiation at all, it's always a dead loss in an antenna.
 

prcguy

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Hand held antennas are nowhere near a perfect match, especially those provided on radios that cover a full band like 136 to 174MHz, etc. A handheld radio is or should be designed to work into a lousy match because they seldom see a good one so I would not worry about a 3:1 or worse match when using a hand held radio.
prcguy
 

LtDoc

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That antenna is a 'fan' type 1/2 wave dipole, it should work just fine. You can lower the SWR a bit by 'tilting' the elements of each dipole. Sort of a very 'wide' 'V' type thingy. How much 'tilt' or the angle between the legs of each dipole? No idea really, it won't have to be much at all.
- 'Doc
 
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