On 7/3/2015 1:06 PM, Wayne wrote:


As for EZNEC and transmission lines, I have never done that, but plan to
when I can. I don't follow how to do it.

Put a short piece of wire somewhere away from the antenna. Move your
source to this short piece of wire. Connect your transmission line
between the short wire and the antenna where you previously had the
source. Put the required line info into the transmission line box(es).
Start with a velocity factor of 1 and an attenuation of 0dB. You should
get the same results as before you moved your source. Then you can
adjust the Vf and loss based on the characteristics of the line that you
can find on line.

Cheers
John N1JLS

On 29/06/15 16:48, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

While I'm pretty happy with the antenna, I'd like to simplify the matching.

Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?


I'm not going to disagree with Dave Platt's post re how the matching on
a 43' vertical works.

As for a simpler way, I'd recommend a remote auto-matcher like an SGC at
the antenna base. It will minimise coax losses and should give you a
good match, at least for most bands. I've used a similar set up (with
radials) and achieved a good match even on 80m.

If your radio has a built in tuner, then it can be used to 'tweak' the
match in the event the radio isn't 'seeing' 1.5:1. Turn it off
initially. Let the SGC find a match. If it isn't ideal, use the local
ATU for a final tweak. I never found this was required but YMMV.

Remember, you really want a low SWR for two reasons, one because modern
radios demand it but also to reduce coax (or feeder) loss. With an
matcher at the antenna feed point, coax losses are minimised. An ATU at
the TX end does nothing to reduce coax losses in real terms.

On Sun, 05 Jul 2015 20:22:19 +0100, Brian Reay wrote:

As for a simpler way, I'd recommend a remote auto-matcher like an SGC at
the antenna base. It will minimise coax losses and should give you a
good match, at least for most bands. I've used a similar set up (with
radials) and achieved a good match even on 80m.

If your radio has a built in tuner, then it can be used to 'tweak' the
match in the event the radio isn't 'seeing' 1.5:1. Turn it off
initially. Let the SGC find a match. If it isn't ideal, use the local
ATU for a final tweak. I never found this was required but YMMV.

Not everyone is a true believer in antenna tuners:
http://www.qsl.net/g3tso/Hombrew-Mobile%20Antennas.html

I've done some admittedly crude testing of various matching
contrivances by measuring the resultant field strength for a given RF
power level (measured at the antenna connector). Although not
conclusive or spectacular, the early model automagic antenna tuner was
rather lossy.

Incidentally, I contrived a rather crude but effective way to measure
relative overall efficiency. I measured the power consumption from
the AC line with a Kill-a-Watt meter (in watts, not VA) and adjusted
the CW RF output for some reference level on the field strength meter.
While this would not give me a real number for the efficiency, it does
produce relative numbers for comparing antenna matching devices.
Unfortunately, I can't find my results, but I do recall that the
winner was a simple 4:1 torroidal matching xformer.

Remember, you really want a low SWR for two reasons, one because modern
radios demand it but also to reduce coax (or feeder) loss. With an
matcher at the antenna feed point, coax losses are minimised. An ATU at
the TX end does nothing to reduce coax losses in real terms.

Coax losses below 500 MHz are mostly in the I^2R losses of the copper
(as limited by skin effect). Above 500MHz, the dielectric gets
involved. See Fig 4:
http://www.maximintegrated.com/en/app-notes/index.mvp/id/4303
Higher RF currents, caused by low impedance terminations, will cause
higher I^2R losses. These higher losses are why very low impedances
are not popular for RF power devices. This has NOTHING to do with
matching. For a given RF current through the coax, the contribution
of the coax to overall losses will be independent of the VSWR.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...

On Sun, 05 Jul 2015 20:22:19 +0100, Brian Reay wrote:

As for a simpler way, I'd recommend a remote auto-matcher like an SGC at
the antenna base. It will minimise coax losses and should give you a
good match, at least for most bands. I've used a similar set up (with
radials) and achieved a good match even on 80m.

If your radio has a built in tuner, then it can be used to 'tweak' the
match in the event the radio isn't 'seeing' 1.5:1. Turn it off
initially. Let the SGC find a match. If it isn't ideal, use the local
ATU for a final tweak. I never found this was required but YMMV.

Not everyone is a true believer in antenna tuners:
http://www.qsl.net/g3tso/Hombrew-Mobile%20Antennas.html


Interesting.
I'm off on a different approach.

I have an RF ammeter mounted in a box. The box is in the shack between the
ATU and the antenna.

I simply adjust the ATU for max current on the ammeter.

On Sun, 5 Jul 2015 17:08:56 -0700, "Wayne"
wrote:
I'm off on a different approach.
I have an RF ammeter mounted in a box. The box is in the shack between the
ATU and the antenna.
I simply adjust the ATU for max current on the ammeter.

Rewind. I just noticed that you're planning to put the RF ammeter
between the ATU and the antenna. That will work, but with
approximately 1200 ohms antenna impedance, you are going to see
50/1200 = 0.04 times the antenna current that you would see on the 50
ohm line between the xmitter and the ATU. If you're running lots of
power, that might work, but offhand, methinks not.

Also, you can't adjust the ATU for maximum current. It adjusts itself
based on it's own internal VSWR sensor. All you can do is watch the
light show and listen to the relays clatter. You might be able to
have some control if it were a motorized antenna tuner. Certainly a
manual antenna tuner would work.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...

On Sun, 5 Jul 2015 17:08:56 -0700, "Wayne"
wrote:
I'm off on a different approach.
I have an RF ammeter mounted in a box. The box is in the shack between
the
ATU and the antenna.
I simply adjust the ATU for max current on the ammeter.

Rewind. I just noticed that you're planning to put the RF ammeter
between the ATU and the antenna. That will work, but with
approximately 1200 ohms antenna impedance, you are going to see
50/1200 = 0.04 times the antenna current that you would see on the 50
ohm line between the xmitter and the ATU. If you're running lots of
power, that might work, but offhand, methinks not.

Also, you can't adjust the ATU for maximum current. It adjusts itself
based on it's own internal VSWR sensor. All you can do is watch the
light show and listen to the relays clatter. You might be able to
have some control if it were a motorized antenna tuner. Certainly a
manual antenna tuner would work.

This isn't something planned. I have been using the ammeter between the
tuner and antenna for many years.

With an automatic tuner, there is no feedback from the ammeter to the tuner.
In that case it is simply an indicator that current is present.

Some of my antennas have SWR outside the capabilities of my automatic tuner.
A manual tuner is used in that case.

With a manual tuner, I don't look for a specific reading, just a peak in the
current from the tuner to the antenna.

On 7/5/2015 7:08 PM, Wayne wrote:


"Jeff Liebermann" wrote in message
...

On Sun, 05 Jul 2015 20:22:19 +0100, Brian Reay wrote:

As for a simpler way, I'd recommend a remote auto-matcher like an SGC at
the antenna base. It will minimise coax losses and should give you a
good match, at least for most bands. I've used a similar set up (with
radials) and achieved a good match even on 80m.

If your radio has a built in tuner, then it can be used to 'tweak' the
match in the event the radio isn't 'seeing' 1.5:1. Turn it off
initially. Let the SGC find a match. If it isn't ideal, use the local
ATU for a final tweak. I never found this was required but YMMV.

Not everyone is a true believer in antenna tuners:
http://www.qsl.net/g3tso/Hombrew-Mobile%20Antennas.html


Interesting.
I'm off on a different approach.

I have an RF ammeter mounted in a box. The box is in the shack between
the ATU and the antenna.

I simply adjust the ATU for max current on the ammeter.

Hey, Wayne -

As a matter of curiosity on my part, can you find a way to measure the
ammeter's resistance and let me know the full-scale value?

Many thanks,
John

"John S" wrote in message ...

On 7/5/2015 7:08 PM, Wayne wrote:


"Jeff Liebermann" wrote in message
...

On Sun, 05 Jul 2015 20:22:19 +0100, Brian Reay wrote:

As for a simpler way, I'd recommend a remote auto-matcher like an SGC at
the antenna base. It will minimise coax losses and should give you a
good match, at least for most bands. I've used a similar set up (with
radials) and achieved a good match even on 80m.

If your radio has a built in tuner, then it can be used to 'tweak' the
match in the event the radio isn't 'seeing' 1.5:1. Turn it off
initially. Let the SGC find a match. If it isn't ideal, use the local
ATU for a final tweak. I never found this was required but YMMV.

Not everyone is a true believer in antenna tuners:
http://www.qsl.net/g3tso/Hombrew-Mobile%20Antennas.html


Interesting.
I'm off on a different approach.

I have an RF ammeter mounted in a box. The box is in the shack between
the ATU and the antenna.

I simply adjust the ATU for max current on the ammeter.

Hey, Wayne -

As a matter of curiosity on my part, can you find a way to measure the
ammeter's resistance and let me know the full-scale value?

No, I don't have enough test equipment to easily do that.

With a DVM it measures 0.4 ohms and with a VOM measures 28 ohms. And the
VOM gives no needle movement.

It is a O. D. McClintock Signal Corp typs I S-III with full scale of 2.5
amps.
Since it was salvaged from some WW II equipment back in the 1950s, it
probably isn't calibrated.

But, it gives a useable relative reading.