Knockarounds

[HomerBB]

Just because it occurred to me to do so I put these two antennas together.
1.) The first was intended to be the driven element of a shortened/coil loaded Yagi. It had great SWR near the ground, but when I put it up over ten feet high the SWR began to go up.
On a lark, I decided to see what it did on the SUV. It was really stinky horizontal over the roof, But when I brought it down and stuck it through the back window vertically the SWR improved greatly and RX/TX was good. I made a make-shift bracket from junk to see how it would do outside the the vehicle.

SWR

27.405 1.3:1
27.185 1.0:1
26.985 1.2:1

2.) The second is simply a horizontal dipole bent inward in the middle to 45*. At 12 feet up it has an impressive SWR.

SWR

28.755 1.1:1
28.305 1.0:1
27.855 1.1:1
27.415 1.2:1
26.965 1.3:1
26.515 1.5:1
26.065 1.8:1
25.615 2.5:1
25.165 3.3:1

Who'd a thought? :blink:

 

[Sonwatcher]

That's pretty cool !

 

[HomerBB]

Because I'm not a very technical person I am always surprised when after reading on something, whether or not I understand it all, then try it, it actually does work.
The thing on the side of the car was a total surprise. . .

 

[wcsd106]

Have you noticed if the horizontal inverted vee is showing signs of being directional at all?

My guess would be that should be directional.

Both look nice.

 

[HomerBB]

Have you noticed if the horizontal inverted vee is showing signs of being directional at all?

My guess would be that should be directional.

Both look nice.

That's what I'm hoping to find out. The night is quiet right now, so maybe tomorrow evening I can check it out.

 

[Marconi]

Just because it occurred to me to do so I put these two antennas together.
1.) The first was intended to be the driven element of a shortened/coil loaded Yagi. It had great SWR near the ground, but when I put it up over ten feet high the SWR began to go up.
On a lark, I decided to see what it did on the SUV. It was really stinky horizontal over the roof, But when I brought it down and stuck it through the back window vertically the SWR improved greatly and RX/TX was good. I made a make-shift bracket from junk to see how it would do outside the the vehicle.

SWR

27.405 1.3:1
27.185 1.0:1
26.985 1.2:1

Who'd a thought? :blink:

I can't tell if the first dipole has wire inside of some PVC or is just tubing, but regardless of what looks like a good SWR, the antenna is too close to the auto. As I see it, being as the antenna is loaded probably makes the problem even worse acting, and is because shortened antennas with loading coils really are affected by stuff close by. I mean "worse acting" in the sense the antenna is working to transmit a bit, but with heavy losses which likely attenuate both the RX/TX. The same goes for the roof mount as well, it needs to be at least 10' feet or better from anything close by or below.

IMO, there are exceptions of course, but it is likely that most mobile installations that show a very low/too low SWR are just not recording the true SWR that exists at the feed point correctly. Thus the antenna is actually showing greater losses that are not so obvious while measuring the feed point impedance with a feed line, and with the antenna being so close to stuff that ill-affects performance. On-the-other-hand, if the same antenna were placed in the open and was clear both around and below for a 1/4 wave with more being better, then the responsive improvements in RX/TX may well be remarkable.

Homer, this thread for some reason is like dejavu, all over again. I know we have talked about a similar issue before. I remember another guy that lived in the desert, out west, having the same problem.

Good luck and get those antennas in the clear and they will work much better for you.

 

[HomerBB]

Thanks Marconi.
It's this kind of info that helps to educate me.
i was able to transmit and receive very well. The idea of putting the loaded dipole on the car was not in the plan, just a thing done on the spur of the moment.

The one on the car is a dipole. It is loaded to shorten the over all length. The lower end is fed by the shield, the upper by the center conductor. It is made of aluminum tubing and the cores of the loads and center separator is of PVC. The loads are #14 solid copper wire.

 

[Marconi]

Thanks Marconi.
It's this kind of info that helps to educate me.
i was able to transmit and receive very well. The idea of putting the loaded dipole on the car was not in the plan, just a thing done on the spur of the moment.

The one on the car is a dipole. It is loaded to shorten the over all length. The lower end is fed by the shield, the upper by the center conductor. It is made of aluminum tubing and the cores of the loads and center separator is of PVC. The loads are #14 solid copper wire.

Plans are always designed to make new plans as you go. When you tried the antenna in the back window, I realized you were flying by the seat of your pants---so to speak. What fun would it be if we never had any surprises?

How did you insulate the mount where it attached to the antenna or the car, or did you have to insulate?

I knew some old timers named Bill and Ted-2025 that use to build 1/2 wave current fed dipoles to be mirror mounted high up on big trucks for guys that had rigs that didn't provide a good ground plane. He used full length whips and they were long. They were installed with a bit of a slant to save a foot or two. A difference was that he built a very small transformer using a small coil that he installed at the feed point. This allowed for a tunable flat match a little above the CB band that he sealed it up and made it fixed tune. He was also a truck driver and sold those things all over the north and north west according to legend.

Once while in Houston, he stop by and told me stories and lies for two hours describing his ideas. I don't hear him any more, but I bet he is still broadcasting somewhere. Some days while he would travel from Wisconsin to Montana, we could talk to him all day long. He also was the designer and builder of the SkyKing monster quad for base operators and they were strong too.

Do you remember our discussions a year or go?

Keep up the good work.

 

[HomerBB]

I do remember the discussions. I just had an experience I wanted to share knowing how little I know. The story of Bill is very interesting.
as for insulating it, I did. Junk pieces of Plexiglas were used for the experiment.
Notice in the photo:

 

[HomerBB]

Ok, I decided to go forward with the three element Yagi. I put the knockround dipole into the Yagi and here are results so far.

Look here:
Loaded 3el Yagi for CB

I will do more work on it and get it up higher later.

The info on the construction of the dipole is now at the above original link.

 

[HomerBB]

Ok, I decided to go forward with the three element Yagi. I put the knockround dipole into the Yagi and here are results so far.

Look here:
Loaded 3el Yagi for CB

I will do more work on it and get it up higher later.

The info on the construction of the dipole is now at the above original link.

Apparently the site is down temporarily. If interested, try again later. Fixed!