Summer activity on 160 AM

[N4DJ]

I just got my original (from 1963)  160 meter rig set up. I have heard and worked a few stations on 80 and 40 AM but would like to find some activity on 160 AM.  I may just have to wait until next fall, but I thought I would post here.
I am in Williamsburg, VA. I have my inverted L up and working again. I could even try daytime for anyone not too far away. 

73,
Don
N4DJ

[Steve - K4HX]

If I had a 160 meter antenna up, we could talk. I'm in Williamsburg too. I've been thinking of putting up an Inverted-L.

[N4DJ]

Be glad to help with your inverted L. Are you a member of WAARC?

[Steve - K4HX]

I'm not a member. Maybe one of these days.

It will likely be this fall until I'm ready to put up the antenna. Have some yard work to do and maybe a few trees to cut.

[N4DJ]

Ok. Drop me an email at n4dj@me.com if you need any help. Consider meeting some of us WAARC guys at a meeting or at breakfast. We get together for breakfast frequently (most every Saturday at various places).  This weekend is at Sandy’s Pancake House Number 1 at about 8AM.
We have at least one other AM guy in the club plus some restoring boat anchors.
I teach a CW class every Thursday night also. Lots going on in the area.
73,
Don
N4DJ

[Steve - K4HX]

Which Sandy's? There are two now.

I may be participating in Field Day Little Creek Reservoir.

[N4DJ]

Steve,
Somehow I missed your question!
I went out to WAARC field day. If you were there somehow I missed meeting you.
Did you make it out?
Don
My email is n4dj@arrl.net

[W4EWH]

I have my inverted L up and working again.

Don, you're just the guy I want to talk to.

I've been helping another ham who has just put up an Inverted-L, and although it's cut to the "proper" length, my antenna analyzer tells me that it's resonant at 1 MHz without the 9:1 balun on it.

So the questions:

• Is an Inverted-L supposed to be worked "off resonance"? I ask because I figure that would raise the radiation resistance and thus cut down on circulating currents.
• Is a 9:1 balun the right ratio for an Inverted-L on 160? I've never seen a balun with that high a ratio.
• If we cut his antenna to resonance on 160, what would the theoretical impedance of an Inverted-L be without the balun?
• What is the best place to trim an Inverted-L? Is the horizontal section just serving as a top hat, or is part of the radiating element, or both?

Please, help me out: my friend thinks I know a lot about antennas! 

Bill, W4EWH

[N4DJ]

Bill,
For one thing you have to be careful trying to read impedance of an inverted L, especially one much longer than a quarter wave. Long story there.

My inverted L is about 179 feet long. That puts the real part of the resistance up higher than if it was only a quarter wave long. However it also introduces inductive reactance. This is not much of a problem as a simple series variable capacitor can cancel the inductive reactance. A variable somewhere from 200 to 500 pf should work. Just put it in series with the coax center conductor and the wire.
The shield of the coax should go to a ground rod. In some cases this works ok and you can get a fair SWR. I usually add at least one radial about 130 feet long. However the more you can add the better. The radials can be on the ground or in the air about 7 feet or so. I have had good luck with all of the above.
Trying to read the impedance of just the antenna wire is not as simple as most people think. You may easily get wrong readings from an expensive analyzer. Especially the R value.
You should have an R value of around 100 plus or minus depending on how good your ground is. This R may not be correct unless you use a series capacitor and tune to minimum SWR. With some analyzers I see an R value of 400 drop to 125 when I put the series capacitor in the circuit.
I would not use a 9:1 Balun.
You can email me at n4dj@arrl.net with any questions. I can send you more info on how to read the impedance of the inverted L and what to look out for to make sure your readings are good. I am presently installing an inverted L ground system. Same 179 foot fire from previous QTH. I have readings taken on three of my 179 foot 160 meter inverted Ls.
Don

[N4DJ]

Bill,
More on the inverted L.
The resonant frequency of mine, just the wire, is at 1.4 MHz. That’s where the X is zero and the wire is a Quarter wave long.
At 1.8 with only a ground rod and tuning the series capacitor for minimum SWR the R is 124 ohms and SWR is 2.9. At this point X is zero. These recent readings were with a RigExpert analyzer.

With the same wire at previous QTH, with radials and tuning the capacitor for minimum SWR I got R=48 and X=zero with SWR of 1.1 on 1.835. The capacitor measured to be 219 pf.  Before the radials I got R = 147 when tuning the capacitor for minimum SWR. Minimum SWR was 3:1. Those measurements were with a MFJ 259B.

[W4EWH]

My inverted L is about 179 feet long. That puts the real part of the
resistance up higher than if it was only a quarter wave long. However
it also introduces inductive reactance. This is not much of a problem
as a simple series variable capacitor can cancel the inductive
reactance. A variable somewhere from 200 to 500 pf should work. Just
put it in series with the coax center conductor and the wire.  The
shield of the coax should go to a ground rod. In some cases this works
ok and you can get a fair SWR. I usually add at least one radial about
130 feet long. However the more you can add the better. The radials
can be on the ground or in the air about 7 feet or so. I have had good
luck with all of the above.

That's more-or-less the setup my buddy has, and we also measured a
large amount of inductive reactance on 160 meters, and we were able to
compensate for some of it by puting a capacitor in series with the
antenna lead. The capacitor was, I admit, in between the balun and the
antenna: not the most effective technique, but it did affect the
readings.

However, at the other end of the RG-8X, we were seeing capacitive
reactance, which I think means that the RG-8X is acting as a
transformer between the [balun input] and [the shack], so we tried
adding inductance at the antenna - again, between antenna and balun -
and it didn't seem to make much of a difference.

Trying to read the impedance of just the antenna wire is not as simple
as most people think. You may easily get wrong readings from an
expensive analyzer. Especially the R value.  You should have an R
value of around 100 plus or minus depending on how good your ground
is. This R may not be correct unless you use a series capacitor and
tune to minimum SWR. With some analyzers I see an R value of 400 drop
to 125 when I put the series capacitor in the circuit.

We were lucky: at least at the antenna, with the balun disconnected, we
got consistent readings. There are three good radials, plus a ground
rod, so I think we've got an effective counterpoise.

I would not use a 9:1 Balun.
[snip]

I wondered about the ratio on that balun: I haven't seen one before,
as I mentioned, and having vertical antenna  with a 450 ohm Z didn't seem
likely, but it's a commercial design, and so I have to ask myself if
I'm looking at this the wrong way.

Before I get to my (long) list of questions, I'll also quote your
second reply:

More on the inverted L.

The resonant frequency of mine, just the wire, is at 1.4 MHz. That’s
where the X is zero and the wire is a Quarter wave long.  At 1.8 with
only a ground rod and tuning the series capacitor for minimum SWR the
R is 124 ohms and SWR is 2.9. At this point X is zero. These recent
readings were with a RigExpert analyzer.

With the same wire at previous QTH, with radials and tuning the
capacitor for minimum SWR I got R=48 and X=zero with SWR of 1.1 on
1.835. The capacitor measured to be 219 pf. Before the radials I got
R = 147 when tuning the capacitor for minimum SWR. Minimum SWR was
3:1. Those measurements were with a MFJ 259B.

We were using a RigExpert AA-600, and a short coax stub with clip
leads on it, and we were seeing ~200 Ohms Resistance and about 150
Ohms Inductive Reactance. Coincidentally, we also saw the reactance
curve cross zero around 1.4 MHz, so your antenna and the one we're
working on here are probably similar.

I've been reading everything I can find about Inverted-L antennas, and
I have a lot of questions: I will thank you in advance for your
patience.

• Is the Inverted-L considered to be a vertical with a top hat, or a half-wave end-fed, or is it in a class by itself?
• Is an inverted-L supposed to be run off-resonance, with a tuner? What are the advantages of doing that?
• Do you adjust your Inverted-L for 50 ohms +j0, or do you use a tuner in the shack?
• What are the benefits of an Inverted-L vs. a vertical?
• What are the disadvantages?
• Do you have any experience with horizontal 160 meter antennas? Can I load one to fit in a smaller space, and still get reasonable signals?
• What's your recommendation for a 160-meter antenna, if I can't put an Inverted-L up?

Thanks again.

73,

Bill, W4EWH

[N4DJ]

Bill,
I will try and answer all your questions.
1. I consider the inverted L to be a top loaded vertical.
2. There are two basic versions of the inverted L. First is the quarter end fed wire. Think of it like a quarter wave vertical with the top bent over. The current at the far end is near zero. It builds up to a maximum a quarter wave back from the end. If fed there the antenna is resonant and has an impedance of 35 ohms plus whatever the ground resistance may be. Usually with a poor ground you get a good match to 50 ohm cable. However there is or may be a lot of ground loss. The current maximum is at the feed point right at the ground. With a really good ground you usually find the SWR goes up, as the 50 ohm coax is connected to 35 ohms (no ground resistance) however you will never have such a perfect ground in the real world. This Z=35+j0 can be measured with a RigExpert.
The other version of the inverted L is in my opinion better. It is longer than a quarter wave. It is a quarter wave down way below 1.8 MHz. This moves the current maximum up from the ground a ways. It also increases the real resistance R of the antenna from 35 to we hope 50 ohms. However since the antenna is longer than a quarter wave it has inductive reactance. Looking into the wire you will have R =50 ohms and X = maybe 300 ohms (inductive). This can not be measured simply with a RigExpert. You may measure Z=400 +j 300 or whatever. Not a good reading in any case. If you put a variable capacitor of maybe 250 or 300 pf in series with the wire and tune it to cancel the 300 ohms of inductive reactance you will then be able to measure Z= 50+j0 with the RigExpert. Your SWR will be close to 1 to 1.
Now this assumes a good ground. The ground R adds to the antenna R. So any time you have antenna R plus Ground R equal 50 you can get a 1 to 1 SWR. Like if the antenna R was 35 and the ground R was 15 you can get the same SWR as if the antenna was 50 and ground was perfect Zero resistance.
So to answer question 2 it is run off resonance and a simple series capacitor at the feed point tunes it to resonance.
3. I do not use a tuner in the shack. Matching an antenna should be done where the coax connects to the antenna. If the wire is 170 to 180 feet long you should get close enough with R. In any case tune the variable to minimum SWR, read the Z with the analyzer and see what you got. The ground or radial system will have some effect. Use at least one 130 foot radial in any case to start. Of course you can test with only a ground rod. I have made many DX contacts over the years with no radials when I first put the antenna up. I always end up with one or more radials.

4. The inverted L does not have to have the top at 130 foot. It can be hung from trees. It can be fed from the bottom easily. A full size grounded tower would have to be shunt fed or have a base insulator. I have had 70 foot towers with a mast extending out the top to about 110 feet. I shunt fed the tower. Most of my 160 meter DXCC was however done with an Inverted L for transmitting.

5. The inverted L may have slightly less gain than a full size vertical. The ground system is probably the deciding factor in either antenna. An inverted L with a good ground should beat a full size vertical with a poor ground.

6. Yes. I have had 160 horizontal dipoles. I think the inverted L is better for DXing. The dipole is better for close in work. I could send you EZNEC plots of a 60 foot high horizontal dipole vs an inverted L if you want.  You can bend the ends of a dipole to make it fit. Not sure how far you can go with that. The center needs to be as high as you can get it. Remember half wave on 160 is 270 feet or so. I have had some good contest scores with the inverted L on 160.

7. I always say that you need to get a horizontal antenna a half wave up. A 60 foot high dipole on 40 meters beats any vertical on that band. On 80 a half wave is 130 feet, so if you can’t get much over 65 feet, use a vertical. I use a half square antenna on 80. That’s phased quarter wave verticals. Fantastic antenna.
On 160 most people have to go with a top loaded vertical. The inverted L is probably the easiest and most popular. You could use a T configuration with two top wires.
The flat top on my L is only about 112 feet long. You could bend the far end down 10 or 15 feet or put a loading coil out on the horizontal section to shorten it if you had to.
A vertical section from 40 to 60 foot works good. The higher the vertical section the better.
Receiving is the biggest issue on 160. Look into a BOG. Only needs to be 200 foot long if you have the room.
I hope this answered most of your questions?
73,
Don

[W4EWH]

When in doubt, consult the 160 Ghods!

W4EWH

[Steve - K4HX]

I did make it to Field Day. Was there from about 6 PM on Saturday until the end on Sunday. Stay up all night! Sorry we didn't cross paths.

Steve,
Somehow I missed your question!
I went out to WAARC field day. If you were there somehow I missed meeting you.
Did you make it out?
Don
My email is n4dj@arrl.net

[K4EMF]

I just got my original (from 1963)  160 meter rig set up. I have heard and worked a few stations on 80 and 40 AM but would like to find some activity on 160 AM.  I may just have to wait until next fall, but I thought I would post here.
I am in Williamsburg, VA. I have my inverted L up and working again. I could even try daytime for anyone not too far away. 

73,
Don
N4DJ

I'm just north of Atlanta.  My 500' loop seems to work well on 160m.  Based on the one or two contacts I've made on 160m anyway.  I'd enjoy trying to make some AM contacts on 160 or any other band for that matter.  Since getting back into ham radio after a 30 year hiatus I've spent much of my time on FT8.  I'm just about over it though.

K4EMF
Jay