Different Look At 102" Whip Discussion

[Marconi]

That pic came from this or not.
Antenna Matching

Yep Lil'Yeshua, Audio Shockwave dug that image up from the website you noted above. This guy is big on mobiles that operate mostly in the 75-40 meter range, using very shortened radiators. In this area of the Ham bands..RF issues are a bit different from 11 meter operations, if that matters to you guys. Check out the very low frequencies used in the examples showing the MFJ analyzer.

Robb, just looking at pictures, as an argument, and without any context what-so-ever can be dangerous to good understanding, but CB guys do it all the time, so knock yourself out.

In an 11 meter mobile your about as good as you're going to get with performance...if your setup shows a true 1.7 SWR or less at the feed point. When the match is indicating 1.1:1 SWR at the feed point such installs are said to have added losses, in order to get the good SWR indication.

I'm not saying, one way or the other will show up as gain in performance, because either way you probably cannot effectively measure the difference in gain or effectivness...just using your radio, inline meter, or an analyzer. Some will argue, in this case, that the better SWR will surely show up as increase in gain, but I say, "...other than just using words, can you show me evidence of that?"

Check out the words in my signature, and think about it maybe making some sense.

 

[ghutch]

The K0BG website is full of good info for mobiles......best site on the web on mobiles and mobile installations...IMO...if someone has a better place pls post it!
The site covers all aspects of installing and getting the best out of a mobile system. I have posted many times the big difference Bonding made to my mobile....I went bonding crazy for a few days and have never regretted a single strap !! I actually was thinking about running a couple more when I install a HF multi band radio in the mobile. Noise levels dropped from sig 7-8 down to below 2. I was not hearing any station below the noise....so it took a 5/9 plus signal to get above all the trash noise generated into the radio. Anyone with a mobile will be hard pressed to find anyway to lower noise that beats bonding the automobile. In that noise level I found multiple Dx stations, unheard before reducing the noise. Now a station with a s-1 signal is workable most times.
My experience with 1/4 wave whips was yrs ago.....it did no better than a mag mount Wilson 1000.....but in those days I did not strap or bond anything! The 1/4 wave was mounted on a rear bumper next to the pickup bed. I'm sure this have a major effect on the radiation patterns and swr. In fact if memory is correct the mag mount did better than or easily as good as the 1/4 wave....it was left on after removing the 1/4 wave.
If I were to use a 1/4 wave today I feel it would be 100% better due to the installation and bonding. Also would never again mount to the rear bumper...only on the roof or cab...might be a head ache for hitting things but that is the best place...if not the only place to mount any mobile antenna.
Bonding does also in my case reduce your swr without cutting or adjusting the antenna. I use a 1000 Wilson it's almost flat in the center and runs over the edges for a good way bot above and below before it get above 2-1. 12 meters is a little high for a long Qso but its just below 2-1...10 mtr is ok to the band edge below 1.5

 

[AudioShockwav]

The reason for using an RF Choke is to limit certain freq that it is passing.

It is not being used as a choke, it is being used as an Inductor to help match the feedpoint of the antenna.

In an 11 meter mobile your about as good as you're going to get with performance...if your setup shows a true 1.7 SWR or less at the feed point. When the match is indicating 1.1:1 SWR at the feed point such installs are said to have added losses, in order to get the good SWR indication.

Due in part to popular press, way too much emphasis is placed on achieving a low SWR. Adding insult to injury, the methodology most amateurs use to check (or set) their SWR is incorrect. A fact which will soon become glaringly evident.

At resonance, the input impedance of a decent-quality, correctly-mounted, HF mobile antenna will be about 25 ohms. By definition, the resonance point is where the reactive component equals zero (X=Ø, or +Øj if you prefer). Since the requisite impedance of our feed line is 50 ohms, the resulting SWR would be 2:1, as read at the radio end of our coax run. However, if you adjust the antenna to a frequency lower than the true resonant point, the indicated SWR will decrease, perhaps to 1.5:1. For this reason, you should use an antenna analyzer with a reactance readout, when adjusting any antenna matching coil or device.

Again, you should look for the lowest reactance (X=Ø), not the lowest SWR when adjusting any matching device. Once the matching device is properly adjusted, the minimum SWR point on your transceiver (or external SWR meter) will be very close to the actual resonance point of the antenna.

Just to make sure this point is as clear as possible... With respect to the input impedance of an antenna (mobile or otherwise) that is other than 50 ohms, when the frequency if moved away from the true resonance point, the resistive component increases faster than the reactive component. In other words, the apparent SWR decreases, however, the antenna is no longer in exact resonance!

You can demonstrate this for yourself by adjusting your antenna analyzer to the lowest reactance (X=Ø, or as close as you can get to it), and noting the SWR. Then, adjust the analyzer's frequency until the SWR is at its lowest, and note the reactance.

Again :

This Post I agree with 100%

Posted By gamegetter.:
Quote:
folks get hung up with swr and try to match by cutting the antenna and throwing resonance off.
I know the example I am about to talk about is a Base antenna, but just to think about, ....the I10-K is tuned by setting the length of the antenna and THEN adjusting the trombone for best bandwidth/SWR.
( then re-read the above and take out the word trombone and insert the words feed-point for just a second)

Now Back to this:
Amateur Quarter Wave Ground Plane Antenna Calculator
The numbers are there, no mater how many times you try it.

And what DOC is saying about
""just because it shows good SWR don`t mean that the antenna is resonate""
many antennas can be the correct length, but exhibit SWR that is real bad, because of several factors.
Design
Feed
Location
Lack of Good Ground plane ( iF the design needs one)

The Matching network is used to match the feedline to the antenna at the feedpoint, while the length of the antenna is at the true resonance point.
Even more important when the antenna is NOT a 1/4 wave......anyone one remember the discussion about the Dave made " Rod Of God Antenna"?
It was a 1/2 wave, and as such the 1/2 wave is at high impedance at the feedpoint so it needs a matching network.
Back to the 1/4 wave, it is close already at 11 meters so (as Eddie has already pointed to) is there any advantage adding the matching network at the feedpoint when there can be small losses in the matching network itself ?

Check out the words in my signature, and think about it maybe making some sense.

I agree with you.

73
Jeff

 

[Marconi]

The K0BG website is full of good info for mobiles......best site on the web on mobiles and mobile installations...IMO...if someone has a better place pls post it!
The site covers all aspects of installing and getting the best out of a mobile system. I have posted many times the big difference Bonding made to my mobile....I went bonding crazy for a few days and have never regretted a single strap !! I actually was thinking about running a couple more when I install a HF multi band radio in the mobile. Noise levels dropped from sig 7-8 down to below 2. I was not hearing any station below the noise....so it took a 5/9 plus signal to get above all the trash noise generated into the radio. Anyone with a mobile will be hard pressed to find anyway to lower noise that beats bonding the automobile. In that noise level I found multiple Dx stations, unheard before reducing the noise. Now a station with a s-1 signal is workable most times.
My experience with 1/4 wave whips was yrs ago.....it did no better than a mag mount Wilson 1000.....but in those days I did not strap or bond anything! The 1/4 wave was mounted on a rear bumper next to the pickup bed. I'm sure this have a major effect on the radiation patterns and swr. In fact if memory is correct the mag mount did better than or easily as good as the 1/4 wave....it was left on after removing the 1/4 wave.
If I were to use a 1/4 wave today I feel it would be 100% better due to the installation and bonding. Also would never again mount to the rear bumper...only on the roof or cab...might be a head ache for hitting things but that is the best place...if not the only place to mount any mobile antenna.
Bonding does also in my case reduce your swr without cutting or adjusting the antenna. I use a 1000 Wilson it's almost flat in the center and runs over the edges for a good way bot above and below before it get above 2-1. 12 meters is a little high for a long Qso but its just below 2-1...10 mtr is ok to the band edge below 1.5

Hey ghutch, I think you answered my question already.

Back in the day, when you had your whip on your P/U truck's rear bumper, did you think your setup was no-way-no...as compared to your local buddies that had their installations done correctly, a distinction you seem to be making here?

When I use to run mobile with my 102" whip on my rear bumper, I never had a bad match like you suggest may be the case. In the beginning of my radio experiences, in the late 60's, I didn't know sickem' from comear', but I would have surely known had my match looked bad. How bad of a match do you think we had back then...runing our mobiles like we did?

I know of guys today that can't talk 5 miles with their mobile setups and others that seem to work just fine at 30-40 miles using side band. I use to talk all over the greater Houston area, maybe 30 miles. For the most part I thought everybody did just about as well back then...talking all over the Houston area. Back then we had a lot of traffic on every channel, just about 24/7, and that was a problem too at times.

If you thought about the ground plane on your typical mobile and without your bonding work, do you think a mobile setup presents a larger or smaller ground plane effect than a 102" radiator with 4 x 102" inch radials slanted down like a Starduster?

 

[Lil'Yeshua]

The only noise I get is when I run the A/C in the mobile is condenser fan noise and my iphone. When conditions are quiet and I'm don't have the A/C on,I have to turn up the volume just to make sure the radio's working.

 

[Marconi]

The only noise I get is when I run the A/C in the mobile is condenser fan noise and my iphone. When conditions are quiet and I'm don't have the A/C on,I have to turn up the volume just to make sure the radio's working.

My recall on noise is about the same Lil'Yeshua. Depending maybe on the radio I used, noise was a fact of life sometimes, and I never had the thought that I could control it like ghutch is suggesting. Then again...I never bonded anything on my mobiles either.

I've heard plenty of similar stories and guys making claims about all sorts of things on CB and on the Internet, while others have said they tried bonding and it made little to no difference in their case.

This is a bit different than a mobile setup for sure, but I've tried many grounding ideas at home on the base in the early years of the 90's, and I never was able to detect one iota of positive effects as a result of such efforts. So, I'm a bit skeptical of noise and static remedies that sorta' sound like fish stories. The idea does however sound plausible, and that makes for good conversation sometimes. However, this also makes the idea very hard to prove either way.

 

[Lil'Yeshua]

I'd like to mount my antenna further back on my mobile's roof but the roof reinforcement ridges doesn't allow a magmount to sit that far back. I have two options. Drill a hole and do a hard mount or support a mounting plate between the luggage rack rails. I'd prefer the antenna to be two thirds back from the edge of the windshield. This gets the antenna farther away from the engine area. Plus i'll mount my Browning noise filter. This will give me more gain towards to front and not look so much like a toy remote controlled car. Anyone know how the make a home brew noise filter?

 

[Lil'Yeshua]

I'd like to mount my antenna further back on my mobile's roof but the roof reinforcement ridges doesn't allow a magmount to sit that far back. I have two options. Drill a hole and do a hard mount or support a mounting plate between the luggage rack rails. I'd prefer the antenna to be two thirds back from the edge of the windshield. This gets the antenna farther away from the engine area. Plus i'll mount my Browning noise filter. This will give me more gain towards to front and not look so much like a toy remote controlled car. Anyone know how the make a home brew noise filter?

Rating is on bottom of label

 

[Lil'Yeshua]

Looks heavy duty
Not good enough. Still had A/C compressor fan noise with it hooked up and had an extra 1 volt drop going through filter when modulating on SSB.



I'm taking this to CRE-8900 discussions and beyond

 

[Captain Kilowatt]

That filter won't do a thing for noise picked by the antenna which in my experience accounts for about 99% of the time. You need beyter shielding/grounding or supress it at tbe source.

 

[Lil'Yeshua]

That filter won't do a thing for noise picked by the antenna which in my experience accounts for about 99% of the time. You need beyter shielding/grounding or supress it at tbe source.

Tell me about it. I don't know how to do what you are suggesting yet. By the way,I took this subject to my CRE-8900 discussions and beyond thread. There you will find a YouTube video I just uploaded about it. If you want to hear what kind if noise it makes. It's a little noisy in the car because it's raining.

 

[BammBamm]

I did my 102 a little different. I had one that the ball on the end had been ground off somehow and was like 101" instead of a 102" So I took a 2 foot section of 3/4" copper pipe and 2 copper caps along with 1 1" bolt to fit into my ball mount and 2 nuts to fit the antenna threads then began construction. I drilled both caps just the right size to fit the bolt through one and the antenna stud through the other. Then I put a nut on the antenna with it through the cap and heated it with a propane torch and soldered the inside of the nut into the cap with the antenna tightened with the nut. Then did the same to the other cap using the bolt through it with the bolt head inside the cap and a nut on the outside tightened and filled cap with solder. Then soldered both caps to the copper pipe one on each end to create a 2 foot extension made of copper at the base of the now too long antenna. I spray painted the tube black and put it in my ball mount and began tuning with a pair of 36" handled bolt cutters and trrimmed the top of the 102" until I achieved a SWR of 1.1 on both ends of the 40 channel band. It actually tuned like 1.5 from 40 under to 40 over the normal 40. I still have the antenna at work but the Chevy S-10 Blazer it was mounted to is gone.{Cry_river} The looks I got with that mounted to the roof on a ball mount where priceless. But God did it talk great. I will be making a new one for my next setup as it was the best mobil I've ever used.

 

[Riverman]

Need some help. Am really confused.

According to the antenna calculators I find online, 1/4 wave on 11 meters is around 103 inches at the middle of the band (27.2). But I am understanding most of you to be saying it is closer to 106 inches (or more).

What am I doing wrong?

Thanks!
Jim

 

[Captain Kilowatt]

Need some help. Am really confused.

According to the antenna calculators I find online, 1/4 wave on 11 meters is around 103 inches at the middle of the band (27.2). But I am understanding most of you to be saying it is closer to 106 inches (or more).

What am I doing wrong?

Thanks!
Jim

What are you doing wrong? Other than paying too much attention to theory and not enough to practical experience nothing at all.

 

[Riverman]

What are you doing wrong? Other than paying too much attention to theory and not enough to practical experience nothing at all.

You got that right, Captain! It's like pretzel M&M's. I can't just eat 'em and enjoy 'em. I have to eat the chocolate off and then eat the pretzel.

Oh, and I like your response a whole lot better than one I got a few years ago when I asked the same question about my golf swing.

"What am I doing wrong?"
"Breathing."