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The 102-inch whip in a perfect world and the real world

slowmover

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Okay, McKenna, this one's for you! :)

102 inches of stainless steel - the standard by which all mobile CB antennas are measured. This true quarter-wave gem has earned the reputation as the perfect pairing for your mobile CB.

The problem with it is that it isn't practical for most of us. If you own a crapper old pickup truck or big boat of a car, a 102-inch whip on the bumper might be ideal. But for a modern personal or family vehicle, it looks like redneck dog poo.

My wife would file divorce papers if I drilled holes in her beloved Pilot and added this giant monstrosity to it. That being said, what kind of suck ass placement is a bumper mount or side mount anyhow?

It is a commonly-held belief that the 102 whip is such a good performer that it generally overcomes a poor mounting position, but to what degree?

How well would this beast work if you could roof mount it?

With kick butt magnet mounts like the Stryker, the Wilsons and other Tram antennas mounted perfectly at the center of the roof and carrying a good SWR, will a crappily mounted 102 still outperform it?

Opinions?
Id say by this point in the thread you’ve understood that wringing every last meter of reception radius isn’t quite going to be overcome by a quarter-wave, and that’s before accounting for other conditions detrimental to the objective.

A roof-center mount with short (town) and long (country) antenna options ought to keep the wife happy. Base load. That approach sure looks hard to beat

I’ll get my truck install done this year. It’s meant to be able to run an almost 15’ tall quarter-wave on the roof (just unlikely to get used much as one needs to be on major highways W of the 98th Parallel). Remind me (I’ll have some kind of thread) and if you want me to try your antenna we’ll figure something out.

Why such a tall antenna desired? A travel trailer behind me that needs about eleven feet of clearance. Getting above that matters. If it doesn’t work as well as I hope it might, I know I’ll have done what I can in that regard.

I have antennas 4.5’, 5’, 6’, 7’ ready to go. Several types. Plus that it’ll be a quite-okay stationary antenna given best location.

The pickup has a bed topper so a stake pocket location is out.

I’d say that a 102” is “best” when bumper-mounted if parked with vehicle aimed directionally over an alternative.

And only then. Big “if”.

Don’t forget to install a shiny copper toilet ball float for coronal discharge.

.
 

K6EEN

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Albuquerque
Correct. When comparing like for like antennas, mounted in the center of the roof of a vehicle, there is a 0.2dB loss for the magnetic mount. It's highly unlikely anyone is going to hear that 0.2dB difference.
All things being equal, mounting the same antenna on a mag mount versus a permanent mount isn't going to amount to much.

However, there's other things you need to consider.
There is a difference between a capacitively coupled ground plane and a real ground plane. That's where the 0.2dB comes in.
I think all those Larsen measurements showing losses for various placements on a vehicle were made at 800 MHz for the old AMPS cellular standard (bag phones with external antenna jacks, if you remember those) and 800 MHz public safety trunking systems. Not sure those measurements apply to most CB, ham radio, and modern cellular systems as the frequencies are very different from 800 MHz by a factor of 2 or more. Or to say it another way, capacitive coupling measured at 800 MHz is going to be very different from capacitve coupling measured at 27.185 MHz. Here's a screen shot of the caption that goes along with that figure from the Larsen literature:

Larsen loss diagram caption.png
 
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bill4long

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Indiana
So what are your thoughts on the bumper-mounted HF whips on military vehicles where they attach to a guy rope on the front bumper?
They legally run a lot more transmit power, so antenna placement is much less important. But, assuming you're talking about legal 4w/12w CBs, then a 1/4 whip in the center of the ground plane is going to be the best. Second best, Wilson 1000 or equivalent at the center of the ground plane. If you don't care about being legal, mount the antenna on the bumper and get a 100w amp.
 

RFI-EMI-GUY

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Dec 22, 2013
Messages
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Id say by this point in the thread you’ve understood that wringing every last meter of reception radius isn’t quite going to be overcome by a quarter-wave, and that’s before accounting for other conditions detrimental to the objective.

A roof-center mount with short (town) and long (country) antenna options ought to keep the wife happy. Base load. That approach sure looks hard to beat

I’ll get my truck install done this year. It’s meant to be able to run an almost 15’ tall quarter-wave on the roof (just unlikely to get used much as one needs to be on major highways W of the 98th Parallel). Remind me (I’ll have some kind of thread) and if you want me to try your antenna we’ll figure something out.

Why such a tall antenna desired? A travel trailer behind me that needs about eleven feet of clearance. Getting above that matters. If it doesn’t work as well as I hope it might, I know I’ll have done what I can in that regard.

snip

.
Why not line your trailer hitch with a Delrin insulator, install RF chokes in line with the trailer lighting/braking lines, and load up the trailer as a centerfed dipole using your truck as a counterpoise?
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
I'll reply to my own post here with a picture of my new truck. Been looking it over for antennas and that will be different than what I thought I could do. For now I'm looking at two NMO trunk lip mounts on the rear of the hood either side of the hinges. Then my military mount with interchangeable plates for NMO, 3/8-24 and a Hi-Q antenna quick disconnect will go on the drivers side upper bed wall about 2/3 back from the cab. I wanted that mount to go on the front bed wall up high and centered on the rear window but the Tonneau cover will interfere with that when rolled up.

The ground plane on the hood mounted NMOs should be fine with that huge steel hood and I have already covered the inside of the plastic cowl parts with wide aluminum tape that grounds to the vehicle body so the ground plane for the NMOs is extended back towards the front window.

The ground plane for the military mount will not be that great but I had very good success running a big HF screwdriver antenna low on the bed wall right behind the cab on a Tundra and this will be about 3 1/2ft behind the cab and higher. The big screwdriver will do CB and if I swap out the top plate on the mount it will take a regular 9ft whip or any other 3/8-24 thread whip. There will also be a matching transformer inside the mount rated at least 500 watts that will provide a 50 ohm, 25 ohm or 12.5 ohm match to the whip, which is needed on the lower HF bands.

Hmm, something about this new truck reminds me of the old Hummer. Maybe that's why I got it. Duhhhh.


truck.JPG

1619671832432.png
 
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RFI-EMI-GUY

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Dec 22, 2013
Messages
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I'll reply to my own post here with a picture of my new truck. Been looking it over for antennas and that will be different than what I thought I could do. For now I'm looking at two NMO trunk lip mounts on the rear of the hood either side of the hinges. Then my military mount with interchangeable plates for NMO, 3/8-24 and a Hi-Q antenna quick disconnect will go on the drivers side upper bed wall about 2/3 back from the cab. I wanted that mount to go on the front bed wall up high but the Tonneau cover will interfere with that when rolled up.

Hmm, something about this new truck reminds me of the old Hummer. Maybe that's why I got it. Duhhhh.



View attachment 102921
I would buy one in an instant if it had an aluminum roof option.
 

prcguy

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Factory is fiberglass or soft top but there are more aftermarket parts for Jeeps than any other vehicle. I wouldn't be surprised if someone doesn't make a metal hard top for these. You can always and easily line the fiberglass with sheet metal or adhesive metal foil.

I would buy one in an instant if it had an aluminum roof option.
 

FiveFilter

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Jan 1, 2016
Messages
285
I could not help myself in "bumping" this picture. "Wireless Mag mounts". The new doctrine.
Yep. Here we go again.

Just can't help it.

Shame to the unwashed nonbelievers!

Drill the hole in your roof or be damned!

Anybody who don't drill a hole in the middle of their $50K car roof is a stupid, embarrassing heathen who is giving away 0.1dB, or is it 0.2 dB, or maybe 0.5dB...we don't know cause we can't tell the difference through the speakers, but they're stupid anyway.

:)
 

prcguy

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I would have drilled mine at the dealer but there is no metal on the roof. And who buys a $50k vehicle these days? You probably don't even get a spare tire for that price.

Yep. Here we go again.

Just can't help it.

Shame to the unwashed nonbelievers!

Drill the hole in your roof or be damned!

Anybody who don't drill a hole in the middle of their $50K car roof is a stupid, embarrassing heathen who is giving away 0.1dB, or is it 0.2 dB, or maybe 0.5dB...we don't know cause we can't tell the difference through the speakers, but they're stupid anyway.

:)
 

slowmover

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Messages
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I think all those Larsen measurements showing losses for various placements on a vehicle were made at 800 MHz for the old AMPS cellular standard (bag phones with external antenna jacks, if you remember those) and 800 MHz public safety trunking systems. Not sure those measurements apply to most CB, ham radio, and modern cellular systems as the frequencies are very different from 800 MHz by a factor of 2 or more. Or to say it another way, capacitive coupling measured at 800 MHz is going to be very different from capacitve coupling measured at 27.185 MHz. Here's a screen shot of the caption that goes along with that figure from the Larsen literature:

View attachment 102920
I’ve seen similar for CB posted often. FIRESTIK probably has it on their 1990s-era info pages, for example.
 

kb2ztx

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They may be available through Motorola dealers but they were expensive, close to $200 I think. I found two on Ebay for reasonable prices, I forget the exact price but under $50. The part # on the box is TRN4505A and its for the Mobat/Micom HF SSB series radios.
I'd love to find a couple of these. Been watching ebay for some time and none. NLA from Motorola which sucks.
 

slowmover

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I'd love to find a couple of these. Been watching ebay for some time and none. NLA from Motorola which sucks.

I looked also. Am well-enough pleased with BREEDLOVE that unless I stumble over a nice MOTOROLA piece to let the search end.

That said, finding a quality spring is a problem. The Hustler 30-series is okay ($30),but the next step appears to be CAL-AV at $100.

rfjunk sells risers of various lengths. Elsewhere have come across those who trimmed the bottom of the whip to keep the assembly to 108”.

.
 

prcguy

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Messages
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So Cal - Richardson, TX - Tewksbury, MA
The Motorola HF mount comes with a really good barrel shaped spring. One of the nicer made ones I've seen.

I looked also. Am well-enough pleased with BREEDLOVE that unless I stumble over a nice MOTOROLA piece to let the search end.

That said, finding a quality spring is a problem. The Hustler 30-series is okay ($30),but the next step appears to be CAL-AV at $100.

rfjunk sells risers of various lengths. Elsewhere have come across those who trimmed the bottom of the whip to keep the assembly to 108”.

.
 
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