choosing an antenna for my new 2m ....

[jeffryscott]

I picked up a Yaesu 1802m Saturday in Phoenix, but am now at a loss for an antenna. I arrived at Ham Radio Outlet just minutes before the store closed and I realized then that while I had spent a fair amount of time researching the various 2m radios, I failed to spend any real time on antennas. With the store closing, I didn't want to rush a decsion so I passed.

What I am finding is too many choices, my little brain is fried trying to figure it out. 1/4 wave, 5/8 wave ... different lengths 20 inches to 96 inches ... :smilies27 .

I have yet to study for the FCC test, so I'm sure some of this will be less confusing once I do, but in the meantime, can folks give me an antenna primer.

What I would like to do, ideally, is mount an antenna where the factory stereo antenna mounts (power antenna that has died, I'm using the secondary antenna on the window). I'd like to do this so the install looks "factory" and uses the hole that is already there.

If nothing like that works, I want a good, basic kit (antenna, mount, coax) that will perform well at a reasonable price (seen anything from $20 to $100).

The radio will be used for basic communication with other rigs on the trail, maybe to listen to search and rescue, etc ...

Thanks for the continued guidance ...

Jeff

 

[Pskhaat]

YMMV, but I'd go with the tallest Larsen NMO antenna (and mount) you can reasonably stand.

It'll be tough to get in the factory hole. There are no mounts of which I am aware that allow that. The mount is very important to maintain proper impedance and thus your performance. There is however a ``trunk-lip mount'' that works perfectly well on the hood seam that could be mounted very close to where the factory antenna is.

All this said, the best thing to do is drill a hole in the center of the roof for an NMO mount.

 

[gary in ohio]

A hustler G7 5/8 over 5/8 ball mounted to the side of a vehicle is always a favorite. after that a good 5/8 NMO mount through the roof. After that anything is a compromise.

Its really going to be on how you use the radio, if you always stay on repeaters and your in a populated area a 1/4 will work, once you get off road a 1/2 or 5/8 is needed. To do a lot of long distance simplex the highest gain biggest antenna will do.

 

[crawler#976]

I guess it depends on what you want to do with the radio...

While I'm still pretty much a novice at the Ham game, I've learned a few things from my experiance's in buying and using two identical units on different trucks. The Taco wears a mag mount 5/8's wave, the BPOS uses a 1/4 mag mount, both radios are Yaesu FT-2800M's. Of the two setups, the 1/4 wave works better.

If you want to achieve the best transmission/reception, a hood/trunk offset mount doesn't offer the optimum ground plane. The center of the roof is the best location for a ground plane. A 1/4 wave roof mount should out perform a 5/8 wave that's offset mounted. The best explination I got on a ground plane is that the ground plane surface should be twice as large as the antenna is tall - so a 1/4 wave antenna works great on a pickup roof, a 1/2 or 5/8's wave should work well on a 4runner. I learned this the hard way by "upgrading" to a 5/8 wave for the Taco, and finding I'd actually lost some performance over the 1/4 wave. That's not to say the 5/8's doesn't work at all - in fact I made a simplex contact on Friday from near the summit of Mt Union south of Prescott, AZ. to Scottsdale at 10 watts with no problem at all. I also can make clean contact with repeaters located in Flagstaff and on Mt Ord northeast of Scottsdale from the Prescott area.

If your only concerned with group comms, a 1/4 wave will do fine mounted anywhere on the rig. It should give you good range on simplex and still get out to most repeaters.

Mark

 

[david despain]

warning: ham noob

i understand how the roof makes for the best ground plane. and how a "trunk mount" in the lip works just fine for most applications and how you will have sub-optimal results that might work ok if part of the antena is below the roofline. i am wondering about antena performance or useability with it mounted to the forward edge of the truck bed. would the bed provide a good groundplane even though the whole bed is below the roof line? it would be pretty easy to mount and keep it out of the way from getting damaged etc. thanks

 

[DaveInDenver]

A hustler G7 5/8 over 5/8 ball mounted to the side of a vehicle is always a favorite.

The Hustler G7 is a base antenna, isn't it? Seems that might be a durability issue off highway?

For single band antennas, my feeling is that a standard NMO antenna is the best bet cost- and performance-wise. Like a Larsen NMO-150 (5/8 wavelength) or NMO-Q (1/4 wavelength), mounted in the middle of your roof.

BTW, as david despain asks, yes a truck bed will act as a ground plane. But it, like any other body panel, must be properly grounded for it to work. Electrical and RF grounds are not the same, so you'll need to at least run a couple of ground braids. You still need to have be aware of the radiation shadow, so if the antenna is mounted lower than the cab and roof, the cab will act to block RF energy. The ideal installation will have the antenna whip completely as high or higher than the highest point of the truck. IOW, you can mount an antenna in the bed of the truck as long as the base of the antenna is at cab height. This sort or defeats the purpose, but doing anything other than that will be compromise and you just need to be aware of that.

 

[david despain]

no to hijack because this is on topic but a ground strap is a ground strap right? a good braided ground strap should serve to carry the ground from bed to frame no matter what shouldn't it? i guess a low quality simple piece of metal riveted to both sides might not work so well but anything i would add would be a good copper braid or thick strap w/ properly crimped ends and it could serve to carry rf signal to ground or provide a ground for electrical devices.
or are you saying that it doesnt need to go to neg battery for rf purposes just to tie all the sheet metal together to make a larger ground plane?

also i understand that the cab will block some signal but for purposes of talking within the group and not trying to reach really far away would it work ok? also as long as the tip is above the cab will this help? i thought it was the tip that was important and not the base is this wrong?

 

[Grim Reaper]

Just a word of caution. My club will not let anybody on the trail with a antenna over 30 inches for safety reasons.

They don't call them a "whip" for nothing. It is very dangerous for spectators or spotters if the truck takes a bounce of shifts violently that antenna will reach out and touch somebody in a unpleasant way. Get a short antenna for the trail and keep the long antenna stored in the back if you need the performance while parked or traveling the hwy.

 

[asteffes]

A 1/4 wave rubber duck mag-mount on the roof always worked fine for me for about 90% of what I used it for. It will be just fine for group comm on the trail. If you buy a generic Larsen or Diamond mag-mount with an NMO or UHF connector on it, you can swap whatever antenna mast you need, when you need it. So rubber duck for trail to avoid damage, 5/8 whip for highway for more range. No, it's not perfect for all conditions but it sounds fine for your purposes.

 

[DaveInDenver]

no to hijack because this is on topic but a ground strap is a ground strap right? a good braided ground strap should serve to carry the ground from bed to frame no matter what shouldn't it? i guess a low quality simple piece of metal riveted to both sides might not work so well but anything i would add would be a good copper braid or thick strap w/ properly crimped ends and it could serve to carry rf signal to ground or provide a ground for electrical devices.
or are you saying that it doesnt need to go to neg battery for rf purposes just to tie all the sheet metal together to make a larger ground plane?

Well, no, not all ground straps are the same. An RF ground strap can act as a good DC ground, but a DC ground does not necessarily make a good RF ground. It's best to use tinned copper braid, which has a much lower impedance (not resistance) to RF. It's entirely possible that a great RF ground could measure significant resistance with an ohm-meter. It's confusing that both resistance and impedance are measured in ohms. But the ground straps used to complete 12V circuits in car wiring are not usually all that great for RF. Also remember that a marginal RF ground might be worse than no ground at all, if it creates ground loops. What is important is that a subpar DC ground to the frame needs to be paralleled with a good RF ground.

also i understand that the cab will block some signal but for purposes of talking within the group and not trying to reach really far away would it work ok? also as long as the tip is above the cab will this help? i thought it was the tip that was important and not the base is this wrong?

The whip radiates along it's whole length, the more length that's up high, the more energy that is effectively radiated.

 

[david despain]

The whip radiates along it's whole length, the more length that's up high, the more energy that is effectively radiated.

ahh gotcha.

impedence is the total resistance of combined capacitance and inductance, no?

this is great info thanks

 

[Pskhaat]

One other thing (Dave, please correct me?) that grounding to the frame proper is not particularly required. It's the sheet metal of the body that provides you your couterpoise.

 

[DaveInDenver]

impedence is the total resistance of combined capacitance and inductance, no?

Impedance and resistance are fundamentally identical, both represent the opposition to current flow. The difference is that impedance is how a reactive component impedes the flow of current to a non-steady state source (alternating or pulsed) and resistance is the opposition to current in a steady state (for example, a DC power source that is not time varying). Impedance is exactly resistance (R) for a resistor, which has no complex component ideally (BTW, they are not actually perfectly resistive in all circuits). But, yes the total impedance for a complex circuit with a non-steady state source includes resistance, capacitance and inductance. You measure the impedance of a complex circuit by:

Just to make sure you are confused, an impedance will also have a phase, which is found by:

But that only deals with the real and imaginary values, not components. So if you are dealing with electronics, impedance is:

Which includes the resistance (R), capacitive reactance (C), inductive reactance (L) and conductance (G). G is the inverse of R, so in a pure resistor in DC, Zo (characteristic impedance) is the square root of (R)/(1/R), or just R. This Zo equation show you the j-omega C and j-omega L. Omega is the physical symbol for angular frequency and is the basis for finding frequency, which is 2*pi*f. The 'j' denotes imaginary numbers and is something that you, well, just have to remember from complex numbers mathematics, where you usually see 'i', which confuses EE who use 'i' for current.

So, impedance includes resistance and they are interchangeable in a DC circuit. A complete solution will always be impedance, which accounts for both the resistance (real) or reactive (imaginary) components.

 

[DaveInDenver]

One other thing (Dave, please correct me?) that grounding to the frame proper is not particularly required. It's the sheet metal of the body that provides you your couterpoise.

Yes and no. You need to ultimately ground to a single point, but not all straps need to run to that single point for your grounding system to work. If it's just a counterpoise you are building, then just connecting a strap between the trunk to the body will achieve that. But the body must eventually run to the frame (or your single point). The radio, antenna ground and counterpoise are all connected at a single point. Some people use the engine as that single point, but I think the frame makes more sense. I connect my engine (for the injectors, ignition, etc.) to the single ground by a strap from the exhaust to the frame. Think of the frame as a great big, huge bolt that is holding all the grounds together. It's electrically awesome and can be functionally assumed to be an ideal conductor.

 

[david despain]

But, yes the total impedance for a complex circuit with a non-steady state source includes resistance, capacitance and inductance.

yeah its coming back to me now. i forgot that resistance is in there as well. its been a few years that i had classes in all this.