Tuner question

[KF6NFW]

When using an auto tuner, which part of the band should I cut for if only ably to cut one length for band. My thinking says the middle of the band as long as the band isn't to wide, past that, I haven't a reason or logic.
So do I cut a flattop dipole for cw on20 or for SSB? Iwill be using 450 ohm ladder line to tuner.and why?

[KM3F]

The answer is wide open.
On an open wire feed through a Balun close to the radio, it likely won't make a huge difference unless you try to use the antenna on other bands.
As long as the impedence presented to the tuner at the radio is within the tuner's range it would make little difference.
What makes the answer wide open is the use of open wire/ladder line where the losses from high SWR are less than if Coax were used (under the higher SWR encountered).
I would adjust the antenna for the part of the band you intend to use the most.
Personally I avoid using an internal tuner due to the higher losses (as much as 10 watts) in favor of an external tuner that will cover several times the impedence range.
Good luck.

[KF6NFW]

this is a brand new MFJ 925 waiting to have its firt taste of RF.
I agree, I am not a fan of internal tuners for most part, but with the TS 520, it really dont complain either if I run 2:1 all day long.
I was using the 20 meter band as an example. having limited space and not quite enough of that for an 80 meter antenna, so I am only interested in 40 through 10 right now. I am starting with a single fan dipole for now with 50ohm coax, and balun, not to bad, but I am also just using at low low level ove 5 and 6 feet, once up at 40 foot level I will know the truth about the antenna.
I was hoping to find a way to get a sloper fed with ladder line to work in my yard, but i dont know much about them.

[K0BG]

No, it really isn't a wide open question. Except for two models from SGC (SG230 & SG235), and one from MFJ (actually made by CG), all currently-marketed auto couplers are LC. Antennas impedances very close to line Z (50Ω) are difficult to match with just an LC configuration. As a result, most of the time it's probably better to cut the antenna a bit short (-j, ≤50R). The SGCs and the one MFJ model, can configure themselves as a Pi when needed, so they don't have the near line Z problem.

I'll agree that auto-couplers are great devices, because the user doesn't have to know what the impedance of the antenna is, as long as it is within the matching range of the coupler in question. However, a decent-quality, "T" configured coupler (you can call it a tuner if you wish, but that's not what they do), will outmatch one easily, and with less loss if it it adjusted correctly. Emphasis on correctly!

[KL7AJ]

When using an auto tuner, which part of the band should I cut for if only ably to cut one length for band. My thinking says the middle of the band as long as the band isn't to wide, past that, I haven't a reason or logic.
So do I cut a flattop dipole for cw on20 or for SSB? Iwill be using 450 ohm ladder line to tuner.and why?

I generally cut for the LOWEST band I intend to operate. This generally results in the best overall efficiency....though you COULD end up with some nulls you don't want on the higher bands.

Eric

[WB2WIK]

I think you should cut the antenna for 14.2201375 MHz, exactly, if you can.

That frequency is the perfect compromise between efficiency and random length.

Seriously, if you're using 450 Ohm balanced line and an auto-tuner, you must have a balun in there somewhere to make that work; I'd use a 1:1 current balun, keep the line between the balun and the tuner very short, and just cut the antenna anywhere in the 20m band. It will not work well on frequencies below 20m, but should work on 20m through 10m okay.

[K6ABZ]

Where are you going to USE it? And are you going with a monoband antenna, or are you going to run multiple bands?

1. If you're going to use the antenna for SSB, then cut it to center in that band segment. If you're going to do digital or CW, cut it for the CW section... if you're going to do both, either cut it for the center of the band, or cut it for the SSB section. Digital doesn't need as much power as phone, so you should optimize the antenna for the place where you need the most output.

2. If you are setting up a true multi-band antenna, than this applies to each band the antenna can handle. With a fan dipole, for example, you're going to cut each leg on the fan for the band segment you intend to use. You'll get "off" bands through harmonics or by exercising your tuner.

3. If you are going to use a monoband antenna and try to tune shorter bands with it, then cut it a little short for your longest band. The reason is that tuners don't like tuning half-wave antennas on a full wave frequency. By shortening your antenna to just above the top of the lowest band you want to work, you're allowing your tuner to tune the even harmonics.

[WB2WIK]

3. If you are going to use a monoband antenna and try to tune shorter bands with it, then cut it a little short for your longest band. The reason is that tuners don't like tuning half-wave antennas on a full wave frequency. By shortening your antenna to just above the top of the lowest band you want to work, you're allowing your tuner to tune the even harmonics.

That's reasonable, but remember on the grossly mismatched bands, the line losses can be quite high which will make the SWR at the transmitter lower. My LDG auto tuners which are "built in" to the Ten Tec rigs I have are amazing...I can load up a 40m dipole on 20m, no problem at all. But the transmission lines are 160-180 feet long and that's part of the reason why that works.

[K8JD]

I only have 2 out of 8 HF antennas that need a tuner to use.
My 80M dipole was originally cut for the Novice band around 3700 and now the CW activity was moved to the lower 60 kHz the antenna is too short. I need to use my internal tuner to make up the difference.
The other is a new balanced feedline/ EDZ/ double Zepp on 20 and 30M this needs my new MFJ balanced tuner to use.
All my other wire antennas were cut for the bottom of thier bands and need no tuner since I'm primarally a CW op.