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SWR when you are running a tuner?

mr_fx

Sr. Member
Oct 8, 2011
1,536
172
173
Kansas City
What is an acceptable SWR if you are running a tuner? What I mean to ask with when do YOU start trimming or adding to your antenna INSTEAD of just tuning the antenna?

For instance my current antenna project has a lower SWR (1.6:1) @ 1.65Mhz, but close to 2.5:1 @ 1.8, and NEARLY 5:1 @ 2.0Mhz now the tuner will tune this and keep the radio happy, of that I have no doubt
 

Looks like it is a bit too long for 1.8mhz to me.
What kind of antenna is it anyway?

Better to have the resonance where it should be. If you are feeding it with coax and it is a flat top dipole; then the SWR should be 1.5:1 at resonance. If it is a inverted "V" dipole; then it should be closer to 1.2:1 at resonance.

Height above ground will also change impedance. Can imagine that you have a 160m dipole up 1/2 the length of the antenna - which would be ~267 ft up. So, if you have it up 10-15m high; that will change the antenna's impedance.

Need more info.

If you can get a hold of an antenna analyzer; that should tell you plenty about your antenna.
 
it's basically a fanned dipole cross bred with a inverted L antenna

so it has 3 aerials, 1/4 wave, cut for 160m, 80m, and 40m on a common feedpoint
 
I'm assuming this is a 160 meter dipole. It's quite a bit too long, and I'd adjust things to get the lowest SWR to fall WITHIN the band.

Then you'll have to make a decision: just where on the band do you want to spend most of your time? CW or 'phone?

You won't find any dipole that will cover 160 from end to end with <2:1 SWR because of the ratio of the frequency span (1.8 - 2 MHz) to the bandwidth within that span (200 KHz).

If it's not a dipole, the same things apply: the bandwidth is a significant percentage of the frequency.

Using a "tuner", you will be able to make the transmitter put out its full power. However, downstream from the tuner, you'll still have a high-to-VERY-high SWR with attendant losses.

The "good" side is that the losses at 160 meters will be fairly small.
 
I will say that the only reason I am showing SWR at out of band areas is because it allows me to 'map' the SWR and find out where the antenna has the lowest swr

however before I trim this antenna I plan to ram 3 or 4 ground rods int othe ground and attach the shield to them (also keeping the 3 ground radials in place)

without the tuner this is what I see

1.5Mhz = 3.4:1
1.525Mhz = 3:1
1.6Mhz = 2.2:1
1.65Mhz = 1.75:1
1.7Mhz = 1.6:1
1.75Mhz = 1.9:1
1.8Mhz = 2.5:1
1.9Mhz = 4:1
2.0Mhz = just under 5:1

so that would seem to indicate that the 160m aerial is about 10.5% too long



3.1Mhz = 3.2:1
3.2Mhz = 2.7:1
3.3Mhz = 2.2:1
3.4Mhz = 2.2:1
3.5Mhz = 2.7:1
3.6Mhz = 3.2:1
3.7Mhz = just under 4:1
3.8Mhz = 4.9:1
3.9Mhz = 5:1
4.0Mhz = 5:1

so it looks like the 80m aerial is almost 12% too long

6.2Mhz = 2.5:1
6.3Mhz = 2.4:1
6.4Mhz = 2.3:1
6.5Mhz = 2.5:1
6.6Mhz = 2.6:1
6.7Mhz = 2.8:1
6.8Mhz = 3.0:1
6.9Mhz = 3.1:1
7.0Mhz = 3.2:1
7.1Mhz = 3.2:1
7.2Mhz = 3.7:1
7.3Mhz = 3.7:1

based on this the 40m aerial is a little more than 11% too long
 
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The idea is to tune the antennas so that using a tuner isn't ~very~ necessary. That will usually have better results than otherwise. Then, if using that tuner will make the input impedance more acceptable to the transmitter, good.
Since you have three antennas in one, and since each will affect the others, finding the right lengths for each is a make changes and check to see if other changes are necessary type of thingy. Count on there being a lot of those changes and checking thingys! That's about as normal as it gets no matter if you're talking about one antenna or a bunch of them. The way you're going about it, finding out what the SWR is at various frequencies, is a very good way of figuring out what has to be done to make things better. Other wise, it's just a shot in the dark, you know?
Somewhere in all that checking and adjusting you will think this is a bunch'a @#$% and just use the tuner to make things 'better'. The quicker you reach that point, the less effective your antenna system is going to be. So, stick to it, don't 'quit' too soon. There's also diminishing returns the 'better' things get. The first change or two can make a big difference, but after that the differences get smaller. You have to decide when it isn't worth more effort.
About that 'grounding'. Ground rods are much less effective than ground radials. Those rods are easier to do than the radials but they just don't end up doing as much. Sorry 'bout that, but it's a fact. If you really want to improve things by adding to the antenna's counterpoise, their 'other halfs', then do the radials instead. (I hate radials, mainly cuz they are a lot of work. Oh well.)
Good luck and have fun.
- 'Doc
 
did a little trimming on the 160m aerial, almost 5 feet

results so far

1.5Mhz = 4.0 : 1
1.6Mhz = 2.8 : 1
1.7Mhz = 1.7 : 1
1.8Mhz = 2.0 : 1
1.9Mhz = 3.0 : 1
2.0Mhz = 4.0 : 1

1.730Mhz = 1.5:1

I have observed no noticeable changes on 80m or 40m (contrary to what many people have suggested)
 
a little more trimming on the 160m aerial

1.7Mhz = 2.9 : 1
1.8Mhz = 1.9 : 1
1.9Mhz = 1.9 : 1
2.0Mhz = 2.9 : 1

1.840Mhz = 1.65 : 1

MUCH BETTER I think it's time to stop. I would like to see it 2.5 : 1 or lower @ 2.0Mhz but this will do

still No changes on the other bands (80m, 40m)
 
Last edited:
a little more trimming on the 160m aerial

1.7Mhz = 2.9 : 1
1.8Mhz = 1.9 : 1
1.9Mhz = 1.9 : 1
2.0Mhz = 2.9 : 1

1.840Mhz = 1.65 : 1

MUCH BETTER I think it's time to stop. I would like to see it 2.5 : 1 or lower @ 2.0Mhz but this will do
Shorten it up but don't trim it, fold it back on itself. That way if you are to short, you don't need to get the wire stretcher out.
 
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