Amateur radio antennas

[Isaac Zachary]

Originally Posted by freebeard

If the antenna is to be removed, and the top center is the optimal location, why not a flush threaded [electromagnetically isolated] hole?

That could very well work, as long as you don't have any "tuning circuits" in the bottom of the antenna that require a connection to the ground plane.

For an example, a 5/8's wave antenna may have an L circuit, which would need to be connected to both the monopole and the ground plane.

You could also just use a tuner instead, placing the tuning circuit farther away (so more loss over the coax), but still should work about the same.

A NMO mount isn't very tall. That's what I use.

[me and my metro]

8.5’ antenna is a quarter wave for hf or cb range. They work well, I could talk all over Southern California with a legal cb back in the 70s. Just park on top of Mt. Lucans above La Crescenta. I mounted mine to the front bumper on my pickup and tied it back when not broadcasting. My trucks at work used loaded twin sticks on top of their mirrors. They are about 36” tall and are less than a half inch in diameter. They are about 8’ apart. There are extendable HF antennas but they are more expensive than a fixed whip.

[redpoint5]

Only useful thing I've done with a CB so far is answer a trucker asking where Walmart was. I told him what exit to take, and he asked if I was the yellow pickup, which I was. He had more questions, so I told him to just follow me as it was on my way homeish.

With cell phones, GPS, and internet, CB becomes less useful for most people.

[Isaac Zachary]

Originally Posted by redpoint5

With cell phones, GPS, and internet, CB becomes less useful for most people.

I suppose. But there are a lot of highways around here that go through dead zones still. I've tried satellite phones but those seemed very finicky. I've also seen the internet, cellphone and landline services all go out for several days.

But even if you have great cellphone coverage, on the road CB radios make a lot of sense. Having a PTT button (Push To Talk) is a lot easier than dialing or trying to talk to your phone to get it to dial for you. And unlike both cell service and FRS you can also put the antenna on the outside of the vehicle making it more effective. CB is also limited to 4W instead of only 3W with cell phones or 2W as with FRS.

GMRS will let you have up to 50W of transmitting power. You can also use repeaters with GMRS. CB isn't great for several dozens of miles, but with GMRS you can put a repeater in the middle and get perhaps 60 miles of range. The downside is that GMRS requires a license. The upside is the license only requires a $30 fee and it applies to your whole family.

Amateur radio lets you have up to 1,500W of transmitting power in the USA, as well as several bands including HF bands that let you bounce off the ionosphere and travel well beyond the horizon. You also get several modes of operation to choose from (AM, FM, Digital, Single-Side-Band, etc.) including video and picture modes. There are also Amateur radio satellites you can use and a whole lot more repeaters available for VHF and UHF use including networks of repeaters that cover the whole state (albeit a lot like or worse than Cellphones, they have their dead spots). The downside is you need to both have a license and take a test, or several tests, in order to get the license.

• Cellphones are like taxis. You rely on the service provided. When it goes out you can't do anything about it.
• CB and GMRS are like driving your own car.
• Amateur radio is like driving the does-all, goes-anywhere SUV as you can even use it to tie into phone lines or send text messages or emails and the like. If the all internet, power and phone lines go out, with Amateur radio I can still contact anyone that receives text messages or emails outside of the affected area via amateur radio.

[ai4kk]

I probably won't be removing it as I do use it for CB while traveling (IC-706MkIIG), but I am taking notes on ideas. Can't go on the roof (or maybe it can, will have to see) as there will be a luggage rack on the left and rooftop carrier on the right for my upcoming trip to WA, plus I often carry canoes/kayaks. I said maybe because perhaps I can put the antennas in the middle and whatever on either side of them. I agree about not teardropping the antenna whip itself as that would be too stiff front-rear.

I do have my questions about sweeping the antennas back some. While that may not be good for a 5/8wave 2m (I'll have to look at the radiation patterns to see how much I can get away with without destroying performance), a quarter-wave antenna is closer to an isotropic source so isn't going to be affected as much. That might be an answer for HF/11M, 2M and 440...just use quarter-wave spikes and tilt them back. How much and how does that help aerodynamics? As far as I know, they sweep the wings on aircraft to delay the formation of shock waves which will probably not be a problem with my Prius...at least not until I get the JATO packs installed :-D

Incidentally, the military tilts their antennas for one to avoid beating them up on trees, but also to take advantage of something called NVIS, or Near-Vertical Incident Skywave. Instead of aiming your radio waves at the horizon so they bounce off a distant ionosphere and come back down hundreds or even thousands of miles away but going right over and missing those closer but past the line of sight, you aim them straight up so that they come back down in maybe a 2-300mi circle around you...kind of like aiming a floor lamp at the ceiling to illuminate the room. We use this a lot in regional communications, especially for emergency services as it tends to be much more reliable for communications past VHF range or closer than the skip zone

[ai4kk]

It's all good and all modes have uses. When I teach emergency communications, I emphasize the importance of understanding the advantages and limitations of ALL forms of communications and utilizing them to their best advantage. For example, if you need to send a list of names or prescriptions, it is going to make much more sense to send them in some sort of email/text-based format than by voice...and if the POTS is up, fax is much more secure for HIPAA info, but if you need to interface with other agencies, CB or GRMS might make more sense. When I was escorting water trucks in Mississippi, I used my HF rig on CB to talk to the trucks I was showing around to fill up the water cubes and when we were on the rooftop in downtown New Orleans evacuating Tulane Hospital, we were on aircraft frequencies to talk to the choppers

Originally Posted by Isaac Zachary

• Cellphones are like taxis. You rely on the service provided. When it goes out you can't do anything about it.
• CB and GMRS are like driving your own car.
• Amateur radio is like driving the does-all, goes-anywhere SUV as you can even use it to tie into phone lines or send text messages or emails and the like. If the all internet, power and phone lines go out, with Amateur radio I can still contact anyone that receives text messages or emails outside of the affected area via amateur radio.

[freebeard]

If nothing else tilting the antennae will reduce the frontal area.

[ai4kk]

Originally Posted by freebeard

If nothing else tilting the antennae will reduce the frontal area.

As thin as they are, how much different do you think this might make?
One advantage I thought of for mounting them all in a row in the middle of the roof is that at least the rear antennas will be in the dirty air from the front ones...but how much drag does a whip present anyway?

[Isaac Zachary]

Originally Posted by ai4kk

As thin as they are, how much different do you think this might make?
One advantage I thought of for mounting them all in a row in the middle of the roof is that at least the rear antennas will be in the dirty air from the front ones...but how much drag does a whip present anyway?

A quick google search says a cylinder has a drag coefficient of 0.3.

So you need to take your diameter and length of the antenna, multiply them together, multiply them by the coefficient of drag, then multiply that by the density of the air, then multiply that by the velocity squared and you'll get how much force it takes to push the antenna through the air, which can also be translated into amounts of energy per distance (like MPG). Of course that isn't including the losses from the engine.

If you angle the antenna then you take the sine of that angle and multiply that by your result and you should get pretty close although I would guess the greater you angle the antenna the more the coefficient of drag would also change, most likely improving (lowering) a little.

SIN(angle) x diameter (meters) x length (meters) x 0.3 x velocity (meters per second) x 1.225 x 0.5 = Force (in newtons)

[redpoint5]

Originally Posted by Isaac Zachary

A quick google search says a cylinder has a drag coefficient of 0.3.

So you need to take your diameter and length of the antenna, multiply them together, multiply them by the coefficient of drag, then multiply that by the density of the air, then multiply that by the velocity squared and you'll get how much force it takes to push the antenna through the air, which can also be translated into amounts of energy per distance (like MPG). Of course that isn't including the losses from the engine.

If you angle the antenna then you take the sine of that angle and multiply that by your result and you should get pretty close although I would guess the greater you angle the antenna the more the coefficient of drag would also change, most likely improving (lowering) a little.

SIN(angle) x diameter (meters) x length (meters) x 0.3 x velocity (meters per second) x 1.225 x 0.5 = Force (in newtons)

Good Will Hunting