Antennas, swr, and tuners, oh my!

[W3MPS]

Ok,

I've been reading up on antenna design for the past three weeks.

I understand that you want the swr to be as close as 1:1 as possible.

Now, from what I understand, if your antenna is not 1:1, a tuner fools the radio into thinking it's 1:1.

With that being said, if I trim the antenna until it reads a close to a true 1:1 on the swr meter. I do not need an antenna tuner. Am I correct?

When I tune the antenna, I was planning to do it at the lowest frequency on each band.

Will some body please explain this bothersome mess to me?

[M0GLO]

You want to trim it to the middle of the band actually.

And a better way than that is to figure out what you are going to be doing in the band, CW/PSK/SSTV/SSB/AM whatever and take a look at the band plan and tune for the middle of your planned operating range.

If you trim out for low swr you won't need a tuner.

I have heard though the best way is not to tune for swr but for maximum signal.
You can use a field strength meter for that and trim till you get max output in the middle of the band.

What kind of antenna you working with?
If it is a long wire you can run another wire parallel to it and close, I forget the distance, to increase the effective diameter of the element. This broadens the resonance curve so you'll get a match over a larger segment of the band.

I really recommend picking up a copy of the ARRL Antenna Handbook as well as the Radio Amateur Handbook.
You only need one copy of each so don't go buying them every year. ;)

[N2RJ]

I have heard though the best way is not to tune for swr but for maximum signal.
You can use a field strength meter for that and trim till you get max output in the middle of the band.


There is some truth to that, but not really with coax fed dipoles. With those antennas, minimum SWR pretty much means maximum output.

Yagis (beam antennas) for sure. Highest gain doesn't always occur at minimum SWR.

[K1OU]

And by the same token, a dummy load has a VSWR of 1.1:1....

[KC8TCQ]

When I picked up the tuner I have now, the gentleman who sold it to me suggested that when tuning I first tune to a frequency close to that I planned to transmit on, where I could hear other signals. Then adjust the inductance to where the signal was coming in the best, then move off frequency , put the rig on low power and AM mode key the mic and adjust to lowest swr. Not sure if that is the "correct" way to do it, but it has worked fine for me so far.

I have worked several islands in the south pacific with it adjusted that way with less than 100 watts on the 20m band on field day, as well as half the US on 10m since june.

[K1OU]

:think

[K1OU]

When I picked up the tuner I have now, the gentleman who sold it to me suggested that when tuning I first tune to a frequency close to that I planned to transmit on, where I could hear other signals. Then adjust the inductance to where the signal was coming in the best, then move off frequency , put the rig on low power and AM mode key the mic and adjust to lowest swr. Not sure if that is the "correct" way to do it, but it has worked fine for me so far.

I have worked several islands in the south pacific with it adjusted that way with less than 100 watts on the 20m band on field day, as well as half the US on 10m since june.

That's pretty much it! Also, a nice antenna site is..http://www.cebik.com

[kf0rt]

I have heard though the best way is not to tune for swr but for maximum signal.
You can use a field strength meter for that and trim till you get max output in the middle of the band.


Quite often, they'll coincide.

When I was playing with my screwdriver antenna on the car, I tried it both ways; SWR and field strength. Maximum field strength always hit right at the minimum SWR point. I'm not sure that would be true for all antennas, though.

From what I've read, a lot of the emphasis on low SWR these days has to do with the solid state transmitter outputs and protection circuitry where you need a low SWR to keep the rig happy and the finals are both expensive and a PITA to replace. Most of the old tube stuff isn't quite so picky.

[n4aud]

Go on ebay or your favorite used book website and get an ARRL antenna book. I've got a couple or three, my favorite was printed in the 70's but they are all good and will explain all the antenna theory and whatnot. The ARRL Handbooks are pretty good too, and you can pick them up a LOT cheaper if you buy them used, like 30 or 40 dollars cheaper! I've got a shelf full of them now, and you should skip 3 or more years between editions to really get any new projects or information. But, anyway, get the books and read them, they've got a lot of good information in them.

Look at getting an antenna analyzer someday too. A bit of expense but well worth it IMHO, Kilroy.

[KC8TCQ]

Go on ebay or your favorite used book website and get an ARRL antenna book. I've got a couple or three, my favorite was printed in the 70's but they are all good and will explain all the antenna theory and whatnot. The ARRL Handbooks are pretty good too, and you can pick them up a LOT cheaper if you buy them used, like 30 or 40 dollars cheaper! I've got a shelf full of them now, and you should skip 3 or more years between editions to really get any new projects or information. But, anyway, get the books and read them, they've got a lot of good information in them.

Look at getting an antenna analyzer someday too. A bit of expense but well worth it IMHO, Kilroy.

Or you can do like I did :shhh: , to go the library. I went there last spring, they had the 2007 ARRL handbook, with the supplemental CD with the electronic version of the handbook in a tabbed PDF format, along with some neat little software packages. I brought the book home, copied the CD onto my external HD, and took the book back to the library heh.

[M0GLO]

Very nicely done Dale!

Something there for everyone! :D

[W3MPS]

:shock:

Alrighty then,

While I really shouldn't be, I am sitting here with my jaw smacking the keyboard.

Dale, thank you for the pile of information you just dropped into my lap.
I will think upon it, consider it, re-consider it, and contemplate.

I was planning on doing a di-pole in the style of the one listed here http://www.hamuniverse.com/multidipole.html

It looks like a winner, but thats just my uneducated opinion.

While I'm on that subject, how well do di-poles work for UHF and VHF?

KC8TCQ, thanks for the library tip. I completely forgot that.

:shhh: (It's how I got my copy of Frampton Comes Alive!)

With all that being said, any opinions on tuners?

I was looking at the FC-30 add on tuner for my 857D. Since it's
a factory (aftermarket-ish) option, how wrong can I go?

Enough of my babbling, I've got physics tomorrow morning.
See you folks later.

[N2RJ]

Dale,

Mind if I put your stuff in the FAQ section?

It would be helpful.

What is SWR really telling us here anyway? Really, it is telling us how efficient our transmission/antenna is matched to our transmitter (assuming the SWR meter is at the transmitter output). This is an important factor to understand to assure our radio is seeing the proper load. But that is all SWR really is. We look for the best match by obtaining the lowest SWR reading.

Antenna gain is another beast altogether. Maybe your antenna has gain, but it is 15 ohms or 250 ohms. What do those numbers really represent? Why is there a resistance when there are no resistors? It's space, man. The resistance is all of the universe out there that you are loading to. You thought you were loading up an antenna. No! You are loading up to the universe. The antenna is the conduit to the universe. How does your antenna transform that signal to the outside world? That is the resistive number in the measurement.

But now, you have antenna that measures 75 ohms at one end of the band and 35 ohms at the other, it goes right through 50 ohms, and darned it! I still don't have 1:1 SWR. It dips at 2:1 or something strange. Okay. Then you have some inductive or capacitive component in your antenna. Sometimes you can clean that up with an inductor or capacitance properly placed, valued and properly rated for the voltage and current requirements.

If you use coaxial cable from your radio to your antenna, I would recommend placing the SWR meter at the antenna input to see what your SWR is at that point. If you can tune your antenna at that point to minimum SWR and you have good cable, your antenna should be most efficient. Remember that different lengths of coax can act like a transformer. It is possible to have very low SWR at the transmitter and high SWR at the antenna input. 50 ohms is a relatively low impedance. If you design an antenna with a high impedance, you don't have to worry about efficiency as much.

[KD8GDM]

A Question , does anyone know which antenna perform best over the widest range of frequencies, 108" whip W/ SGC type tuner or Screwdriver ? I Want to exercise my Extra status, so I must upgrade radio and antenna. Without the Multi antenna "wacker look" Since I live in Michigan, the salt build-up on the screwdriver concerns me also.Thanks Bear, KD8GDM jlyrgr49@aol.com

[N9FE]

Well how big is your wallet. Screwdriver type will get the most but also cost the most. The 102 whip thing is 10 and 12 only. You put a tuner on that, you would be wasting your time. N9JMX bob in indiana builds some of the best mobile antennas, but there not cheap. Texas bugcatchers are cheaper. Remember for any kind of results you HAVE to get the coil above the roof of whatever your driving. And then start grounding, grounding. And grounding some more. I don't what to seam like i'm preaching to you. But if your going to go mobile. these are the things you have to do. otherwise you will be talking to yourself and knowone else. an amplifier is a good idea also. Without one on the low bands 40-75-80. 100 watts will work. But when you have daylight or 20 over lightning conditions you'll know why. You can do very well mobile. But do your homework. Talk to people that do it everyday and that will keep you spending money on things that don't work.

[kk7ue]

Well how big is your wallet. *snip* But do your homework. Talk to people that do it everyday and that will keep you from spending money on things that don't work.
Fixed that for ya :mrgreen:

[N9FE]

Yeah i don't know how to explain myself with a dam keyboard. call me on the phone or on the radio and you will hear the difference. if anyone got pissed off or offended i'm sorry. i ran bulldozers all my life not keyboards...

[W5GA]

A Question , does anyone know which antenna perform best over the widest range of frequencies, 108" whip W/ SGC type tuner or Screwdriver ? I Want to exercise my Extra status, so I must upgrade radio and antenna. Without the Multi antenna "wacker look" Since I live in Michigan, the salt build-up on the screwdriver concerns me also.Thanks Bear, KD8GDM jlyrgr49@aol.com

Mobile or home?
Local (within N.A.) or DX?
What budget?
What're your interests?

The answers will narrow the field considerably.