Antennae question

[ebg18t]

I am running a Icom 208H in the truck. Using the Comet lid mount with Comet SBB1 NMO antennae (specs below)

SBB-1NMO , Flexible DualBand , 146/446MHz
Gain & Wave:
146MHz 1.5dBi , 1⁄4 wave
446MHz 2.15dBi , 1⁄2 wave
VSWR: 1.5:1 or less
Max Power: 60 watts
Length: 16”
Connector: Gold-Plated , PL-259 or NMO style

I am thinking about getting a longer antennae for better range and was looking at the below model from Comet.


SBB-5NMO, DualBand 2M/70cm mobile antenna
Gain & Wavelength:
146MHz 3.0dBi 1⁄2 wave
446MHz 5.5dBi 5⁄8 wave x 2
VSWR: 1.5:1 or less
Max Power: 120W FM
Length: 38"
Connector: SBB-5 Gold-plated PL-259, SBB-5NMO NMO

Realistically what will I gain from the longer antennae? How can I quantify it, yes I know this is very basic. But I am still learning.

 

[DaveInDenver]

Theoretically your range transmitting with 50 watts to a receiver with -85dBm sensitivity and 5.5dBi antenna would go from 27 miles to 35 miles. On 70cm assuming the same parameters (50W and 5.5dBi receiving antenna and -85dBm sensitivity) your theoretical range would go from 26 miles to 44 miles. The formula you'd use for this is Friis Equation.

In the real world you probably won't see a great deal of improvement on 2m compared to what you have now but on UHF you'll probably see an obvious improvement in range. The increase in horizontal range will come with less overhead range. You might notice some fading if you're at the fringe of reception and the antenna is flopping around in and out of polarization, for example.

Primarily it comes down to whether or not the longer antenna will work on your truck, parking it and the like. If so, there's not much down side to a longer antenna. Are there stations or repeaters that you are barely hitting that you want to hit a bit more reliably? On 2m you'll probably see about an S-unit increase but on UHF you'll probably go up a couple of S-units.

Just FYI, singular is antenna and plural is antennas. Bugs have antennae.

 

[ebg18t]

Just FYI, singular is antenna and plural is antennas. Bugs have antennae.

Damn auto correct on ipad got me again. But i will leave it for others to get a chuckle out of it

I was looking at the longer antenna for trip use (no cell coverage) when i don't need to worry about garage clearance and things like that. The 16" rubber one is handy since it is short and flexible. It seems like the gain on 70cm could be very noticeable, especially in areas with less repeaters. Thanks for bringing up Friis equation, i can look that up now.

But like you mentioned with the longer antenna the swinging around could result in it going in & out of polarization? Is there a way to prevent/reduce it? Would a different antenna work better? I looked at the Comet as that is what i had now.

 

[DaveInDenver]

A stiffer antenna would help but the Comets are AFAIK fairly rigid. You don't want a mobile antenna that's too stiff, then they break. I wouldn't worry about it to be honest and having two antennas is very common. I run 1/4 wavelength whips most of the time and have longer whips for road trips and stuff. Antennas are what it's all about and we hams tend to collect and experiment with them endlessly.

The antenna/antennae/antennas thing is just a one-man crusade, I don't know if anyone else really cares.

 

[Crom]

In the opening post, it says your using a lid mount, but that doesn't really tell us where it is... where exactly on the vehicle is it mounted? trunk hatch? front fender lip? etc.

 

[gary in ohio]

The SBB-1NMO is a glorified dummy load so no wonder your looking to upgrade. Most of your power is being lost in the antenna. The SBB-5NMO would be a world of improvement

 

[ebg18t]

In the opening post, it says your using a lid mount, but that doesn't really tell us where it is... where exactly on the vehicle is it mounted? trunk hatch? front fender lip? etc.

Pics usually help. Should have posted this before.

 

[DaveInDenver]

The SBB-1NMO is a glorified dummy load so no wonder your looking to upgrade. Most of your power is being lost in the antenna. The SBB-5NMO would be a world of improvement

That's not fair, it's an OK UHF antenna and just a simple, if flexible, 1/4λ on 2m. I'd personally think the reason for any poor performance is that it's lip mounted rather than over a plane, which would make a significant improvement on 2m with that antenna. I run a 1/4λ 2m antenna Sti-Co Flexiwhip and a 1/4λ Larsen 70cm through a duplexer daily, range is not a problem for me but they are mounted in middle of my roof.

Of all the Comet antennas I think it's one that does what it says it does, simple and seems built well enough for a rubber ducky. Unlike their fancier models that use all sorts of tricks to achieve silly idealized numbers only seen in a chamber and use delicate construction in the coils.

 

[Crom]

... I'd personally think the reason for any poor performance is that it's lip mounted rather than over a plane, which would make a significant improvement on 2m with that antenna. I run a 1/4λ 2m antenna Sti-Co Flexiwhip and a 1/4λ Larsen 70cm through a duplexer daily, range is not a problem for me but they are mounted in middle of my roof.

^ This is what I was getting at. Larsen published this photo illustrating the losses when not mounting the antenna in the optimum location. I strongly recommend to anyone doing antenna research to read through their Amateur Antenna Products Catalog as it's very helpful to make informed purchasing decisions, even if it's not a Larsen product.

I happen to run one of their NMO2/70 antennas It's 34" tall. I mounted it on a light tab on my steel-mesh-floor BajaRack. I can cleanly hit UHF repeaters 115 miles away if LOS is good. That's transmitting in San Diego to Pasadena (Mt. Wilson) using just 10 watts. I don't have enough experience to know, and I'm not sure about anybody else, but that's pretty impressive to me.

 

[Cabrito]

That's not fair, it's an OK UHF antenna and just a simple, if flexible, 1/4λ on 2m. I'd personally think the reason for any poor performance is that it's lip mounted rather than over a plane, which would make a significant improvement on 2m with that antenna. I run a 1/4λ 2m antenna Sti-Co Flexiwhip and a 1/4λ Larsen 70cm through a duplexer daily, range is not a problem for me but they are mounted in middle of my roof.

Of all the Comet antennas I think it's one that does what it says it does, simple and seems built well enough for a rubber ducky. Unlike their fancier models that use all sorts of tricks to achieve silly idealized numbers only seen in a chamber and use delicate construction in the coils.

I agree with Dave on the SBB1,
I've been using a SBB1 for a few years and it seems to work just as well as my much longer Diamond NR770HB – I do switch to the Diamond when I think I need longer range, but found them to be about equal.

Disclaimer –
I'm only a real basic user who does not get too caught up on specs or details. I just need some basic HAM communications.

 

[ebg18t]

So with all this mount talk ya'll are indicating using a lip mount like I did actually hurts performance. How can I improve the mount to increase performance?

 

[DaveInDenver]

So with all this mount talk ya'll are indicating using a lip mount like I did actually hurts performance. How can I improve the mount to increase performance?

On a lip mount or overall? With a lip mount make sure the body panel, be it a door or rear hatch or whatever, is well bonded to the rest of the car body. Beyond that run an antenna that is relatively ground plane independent, which would be the 1/2λ lengths. Any antenna that is 1/4λ or a multiple of that will rely on a ground plane to work and will be greatly affected by the lack of one. The best thing you can do is drill a hole for an NMO mount right in the middle of your roof or trunk lid, which you can see from Crom's linked photo is a 2.8dB increase in efficiency alone. That's the equivalent of doubling your effective power.

 

[ebg18t]

So basically my current setup is 1/4 wave on 2m and 1/2 wave on 440. So with a lip mount I am kinda screwed. The rear hatch is secure and I have made sure the lip mount is solid. But without drilling it appears i am compromising.

 

[Cabrito]

So basically my current setup is 1/4 wave on 2m and 1/2 wave on 440. So with a lip mount I am kinda screwed. The rear hatch is secure and I have made sure the lip mount is solid. But without drilling it appears i am compromising.

Life is full of compromises.

What's your definition of “Screwed”? likewise what do you need for “better range”? What kinds of distances are you talking about?

It's all relative. Lots and lots of Hammers are using lip mount antennas with great results.

 

[Crom]

If it were me, I would definitely upgrade to the SBB-5NMO antenna, like Gary said. I think it would definitely help. I'd probably stop there. However, I see you have a BajaRack or some similar type roof rack, depending on how much time / energy I had I would consider migrating the mount up there above the roof line. That's what I did with mine, so no drilling required.