My First Attempt At A Mobile Antenna

[cbrown]

Let us know how it performs.

[homerbb]

Dec 8, 2010 10:50:26 GMT -5 cbrown said:

Let us know how it performs.

ok

[homerbb]

Still working on the antenna.

[Sandbagger]

Dec 14, 2010 23:55:09 GMT -5 homerbb said:

Still working on the antenna.

I've got to say, that antenna is looking more and more like a commercially made product. It has to be working pretty good by now. It sure looks good......

I like the irony of a CB antenna sitting on top of the ARRL handbook............ ;D

[cbrown]

Good book to read.

[homerbb]

Dec 15, 2010 8:54:27 GMT -5 Sandbagger said:

I've got to say, that antenna is looking more and more like a commercially made product. It has to be working pretty good by now. It sure looks good......

I will get this one on the SUV today. Hopefully I'll regain some distant performance with the newer dimensions. With four models I hope to remount each one within a few minutes of each other and make comparisons to the same 20 miles distant base station.

Dec 15, 2010 8:54:27 GMT -5 Sandbagger said:

I like the irony of a CB antenna sitting on top of the ARRL handbook............ ;D

Ssshhh . . . don't tell them.

[homerbb]

I've got it top of the SUV, now.

[Deleted]

No way I could do that. My work requires me to park in garages. You know have many time I forgot to unmount my Wilson? LOL ;D

[homerbb]

Dec 16, 2010 8:12:33 GMT -5 @vinnies said:

No way I could do that. My work requires me to park in garages. You know have many time I forgot to unmount my Wilson? LOL ;D

I park in the garage here at home. I remember to lay it down, or the wall knocks it over.

[homerbb]

I now have five different models. I intend to build my roof mount so I can replace the antennas quickly. I want to test them against each other and a bottom coil magnet mount K40 as well as a 102" SS whip. There are two distant base stations I want to get to help me with the comparisons.
Soon.

[homerbb]

I've begun the process of making comparisons between the several models of the antennas I built to each other, a K40, and an straight 1/4 wave whip.
First of all I had to put a reliable means of mounting the antennas on the roof of the SUV with quick change capabilities. Where this antenna is attached to the mount on these two photos I put a 3" piece of PVC into which I dropped each antenna shaft with a set screw through the PVC wall into the bottom of the antenna shafts. To this set screw I attached the coax center conductor. Here is the mount:


Next I mounted the antennas one after the other on the roof and reset the SWR across the band capabilities of the SuperStar 3900 in the mobile. I was dead keying 3/4 watt, swinging around 12 watts PEP; no kicker online. I was talking with a base station 10 miles from me, I will do a 15 or 20 mile base station later when I can get them to cooperate for a little while. The antenna on the base is a vertical groundplane with the coax connector at 70' above ground. He was talking to me with 2 watt dead key. I do not know what his PEP is at this time.

The antennas are a K40:


a whip:


By order of build -
#1 homebrew:


#3 homebrew (#2 was rewound into this one):


#4 homebrew:


#5 homebrew:


Here are the results so far:


What I will have to do, perhaps tomorrow, is add the overall dimensions of the various antennas in an additional post. It got dark on me today..

[Sandbagger]

Dec 21, 2010 22:03:51 GMT -5 homerbb said:

I've begun the process of making comparisons between the several models of the antennas I built to each other, a K40, and an straight 1/4 wave whip.
First of all I had to put a reliable means of mounting the antennas on the roof of the SUV with quick change capabilities. Where this antenna is attached to the mount on these two photos I put a 3" piece of PVC into which I dropped each antenna shaft with a set screw through the PVC wall into the bottom of the antenna shafts. To this set screw I attached the coax center conductor. Here is the mount:

Next I mounted the antennas one after the other on the roof and reset the SWR across the band capabilities of the SuperStar 3900 in the mobile. I was dead keying 3/4 watt, swinging around 12 watts PEP; no kicker online. I was talking with a base station 10 miles from me, I will do a 15 or 20 mile base station later when I can get them to cooperate for a little while. The antenna on the base is a vertical groundplane with the coax connector at 70' above ground. He was talking to me with 2 watt dead key. I do not know what his PEP is at this time.

The antennas are a K40:

a whip:


By order of build -
#1 homebrew:

#3 homebrew (#2 was rewound into this one):
#4 homebrew:

#5 homebrew:

Here are the results so far:


What I will have to do, perhaps tomorrow, is add the overall dimensions of the various antennas in an additional post. It got dark on me today..

I love doing antenna comparisons like that. If you do your best to make the conditions as close as possible, the results can be interesting. More interesting is just how close the results can often be, which pretty much shines a bright light on just how much hype there is between antenna manufacturers.

But as a suggestion, I would try to de-emphasize any comparisons using PEP numbers. They are hard to reliably reproduce, and some radios will show less swing (and some will go backwards) than others. Your best bet is to go strictly by dead key carrier signals. That way you can back down the rf gain (On stronger signals) and put the signal into the radio's most sensitive area, and you can differentiate even the width of a needle difference. That's hard to do with moving signals (PEP).

But it looks like your homebrew antenna is as good as a whip and pretty broadbanded to boot.

[homerbb]

I tend to agree with all you've said. Why I chose to put the PEP in is because someone will inevitably ask for it. As for "the conditions as close as possible," I tried to do just that: I switched out the antennas in seconds by utilizing a quick release mounting system. I used only the one radio in the mobile, all on the same coax, and tested to the very same receiving station all from the same location - my driveway. He reported to me my DK, and then using the word four, the PEP at the receiving (base) station end. All the antennas were mounted and tuned to the reported SWR before the test started. The time lag between changes was as long as it took to reach up, release the antenna, and put the next one in place. It was the best I could do to maintain a controlled environment.
I hope to do it with a field strength meter, stationary mobile-to-mobile, and a base at greater distance at a more common height of less than 70' to feed point. In these hills most setups are not that high up.

[cbrown]

Dec 22, 2010 9:14:21 GMT -5 homerbb said:

The time lag between changes was as long as it took to reach up, release the antenna, and put the next one in place. It was the best I could do to maintain a controlled environment.

Sounds to me that you did the comparison in pretty close to optimum conditions that you could do, without actually being in a laboratory.

Nice job!

[homerbb]

Thanks cbrown. I tried.
New info regarding antenna dimensions:

[homerbb]

Another attempt and on the mobile:

[homerbb]

I threw this together yesterday. No testing other than to temporarily mount it on the SUV and check SWR on CB band. More finessing it to be done, but it works.

[cbrown]

Looks very nice!

[homerbb]

Thanks

None of the others were suited to a magnet mount, so I figured to try something that could be driven at high speed without a hard mount of some sort.

[homerbb]

SWR:
28.305 ----------- 1.8:1
27.855 ----------- 1.4:1
27.555 ---------- <1.2:1
27.405 ----------- 1.1:1
27.205 ----------- 1.1:1
26.965 ----------- 1.1:1
26.515 ----------- 1.3:1
26.065 ----------- 1.7:1
25.615 ----------- 2.2:1

[cbrown]

If you get a design you really like, you should see if you can get the antenna silver plated. Silver plating the tubing further reduces losses.

[homerbb]

Are to talking about chrome? Silver sounds expensive.

[cbrown]

Silver plating isn't too expensive, it depends on the thickness of the plating and the prep work required. But it is worth the expense. At RF frequencies, power/electricity only travels on the surface of the conductors, so silver plating the antenna wires and coils/inductors offers optimum performance. Silver is the best 'low-loss' most efficient metal on earth, especially with RF.

Silver-plating also lasts much longer than just 100% copper, as it helps protect the copper from oxidizing or corroding. Silver oxidizes slower, so surface coating copper also protects the copper underneath it. The most amazing property of silver however, is that even when or if silver does oxidize, that oxidation itself is still highly conductive of RF.

[homerbb]

Interesting I'll look into this.

[cbrown]

I wouldn't do it until you settled on a final design.

[homerbb]

Makes sense. I looked t up, and apparently the ingredients are considered available locally. Now a decision would be in order. . .

[cbrown]

Ya, finalize your design, get it how you like it before doing the plating.

[homerbb]

It's something I've never done, but I'm pretty sure I will. Too interesting not to.

[homerbb]

Another one. Got bored with the cold weather so I spun another. Not silver plated, bur chrome on the shafts.

[cbrown]

Looks great, Homer. You're really doing some nice work.

Antenna design was always a favorite thing for me, also.