Another Antena Question

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sprocket3

sprocket3

Joined
Nov 9, 2005
Threads
46
Messages
585
Location
Portland, Oregon
Hello,

Can one of you HAM experts tell me if this would be a good antena system or if i'm doing anything wrong. Just want to pick this up if it looks good but very new to HAM.

I just purchased the new Kenwood TM-V71A dual band 2/440 with 50 watts on both bands.

Thinking about rear hatch for a mounting site.

What about this system:

Mount: K400-SNMO
Includes: NMO base to SMA with 13.5' C-series teflon coax cable. PL-259 adapter.

Regular Antena: Diamond NR770ohnmo
38" 3/5.5gain NMO mount.

Trail Antena: Some 20 inch shorty like the Comet SBB-2NMO

Questions:

1) Will that be enough coax to go from the hatch to under the pass side seat?

2) Is NMO the best mount for this. Seems there are more short antenas in SMA. What about SO-239? Lost here.. Want to be able to change it real quick on the road.

3) With this setup does the antena hit the top of the cruiser when you open the rear hatch or does it go only to horizontal.

4) Is C-Series coax cable good stuff, or can do better?

5) How do i know if this system is "matched" to my radio?

6) Is it reasonble to look at anything bigger than the 40 inch range as mentioned above? Seems like the next step would be around 60 inches and include those loading coils that are easily damaged. Is it worth it?

Thanks in advance for any information.
 
Sprocket,

I went with Diamond's K400C heavy duty mout .
To get the cable inside the cabin and not go under the weather strip, I drilled a hole on the body of my cruiser.
More info on my web page.
This is how the mount is described by Diamond: "K400C Trunk/Hatchback Mount . Diamond® heavy duty mount with UHF base. Strongest, most universal mobile mount available. 2-axis adjustment."

Others might correct me if I'm wrong, but I don't think you need a NMO mount since your mount isn't going through the roof of your vehicle.

Regards

Alvaro
 
Alvaro,

I think i'm sold on that mount. Just trying to decide what antena and cable setup.

That Comet CSB770A looks like a great one, just thinking about 51" on the back of the hatch might be too much. But it gets 4.4dbi of gain on 2m. But has the "coils" that might not hold up in the trees very well. It's always a compromise!

Getting close though
 
I'm on the fence! I do think that the 770 comes in a fold down model as well as fixed though.

How much difference is there between a 3 db gain and 4.4 db gain in real life. That's almost 50% increase in gain. Does that get me 50% more range?

What would be better: A smaller antena higher on the truck, or a large antena pulled down a little on the hatch?
 
sprocket3 said:
Questions:

1) Will that be enough coax to go from the hatch to under the pass side seat?

2) Is NMO the best mount for this. Seems there are more short antenas in SMA. What about SO-239? Lost here.. Want to be able to change it real quick on the road.

3) With this setup does the antena hit the top of the cruiser when you open the rear hatch or does it go only to horizontal.

4) Is C-Series coax cable good stuff, or can do better?

5) How do i know if this system is "matched" to my radio?

6) Is it reasonble to look at anything bigger than the 40 inch range as mentioned above? Seems like the next step would be around 60 inches and include those loading coils that are easily damaged. Is it worth it?
Click to expand...

1) Yes, that should be enough length depending on which side of the truck you put the antenna and the radio. Be aware that there is almost no room under the PS of your 80-Series. Dunno about the 100-Series or your other vehicles. (You didn't state which was getting the radio.) I mounted my radio under the driver's seat of my '97 Land Cruiser. The alarm remote needed to be moved a few inches but that was very easy to do.

2) I selected the NMO mount based on the recommendation of others. It is pretty sturdy and easy to swap antennas.

3) The antenna will not hit the roof if you mount it high enough on the lip of the hatch. The antenna goes horizontal. (Again, talking about the 80-Series hatch; not your 100-Series)

I cannot answer questions 4, 5, and 6.

-B-
 
sprocket3,

I've used the Diamond NR770BNMO antenna and like it. The whip part can be pulled out (it's spring loaded) and folded down. It doesn't do it on it's own so it could get broken if it hits a tree limb while in the up position. I used it mounted on the hood lip and never had to worry about it hitting something.

In May I bought the same Diamond K400SNMO mount you mentioned. I like the small Teflon coax. Attenuation is not bad with only 13 feet of length and it's easy to bring into the inside of the truck. I connected it to the radio with an SMA female to PL259 adapter. I know others like the side lip of the rear hatch, but I mounted it on the wind deflector. The small coax goes inside the truck at the top between hatch seal and jam, along the passenger side window then down the rear of the rear door and under the carpet to the center console. It just makes it, so it should make it to your passenger seat just fine. I didn't drill a hole for the coax. It gets sandwiched between the hatch weatherstrip seal and truck door jam.

With this mount position I switched to the Diamond NR73B antenna. It's shorter than the NR770 but still has good gain. It doesn't need a ground plane and works great on the wind deflector. Not too much drag to get ripped off, not too tall, and when the hatch is open it lays down about 3-6 inches from the roof. I sometimes have left it that way with the hatch open and forgot to turn off the radio while the APRS was beaconing at 50 watts. The SWR may have been high, but it didn't damage the radio and the position reports got out some distance (don't know how far).

You shouldn't have to do any tuning. After connecting everything right "out of the box" the SWR measured about 1.1 - very low!

While daily driving I unscrew the antenna and keep it inside. The mount is hidden behind the wind deflector.

If you're going to be around a lot of tree limbs or low obstacles, you may want a different antenna. I would probably buy a Larsen dual band whip and coil and not worry about it getting broken or bent. They have different styles/lengths and some are spring loaded to bend over if they get hit.

Guess that's about enough info. Good luck with your setup!
 
Hey guys. Thanks for all the great info. I'm at work and just checked the site. Picked up what i needed yesterday and started the install. Was up to 11:00pm in the garage pulling wire.

GOING IN THE LX450!

Ended up going with PL-259 k400 mount.
one SBB2 20 inch solid with loading coil.
one SBB5 40 inch with flex spring type coil.

I got the brain under the drivers side seat. Fits nice once i moved the alarm a few inches as well. Ran the antena from the drivers side and came out perfect with about a foot to spare under the drivers side seat.

I'll post pics of the install when done. I think it will come out cool. I'm going to build a custom mount for the faceplat and put it above the mirror hanging down. Mic is next to the E-Brake handle.

Just need to figure out where to put a speaker.
 
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sprocket3 said:
Just need to figure out where to put a speaker.
Click to expand...

I put the external speaker between the mounts for the DS headrest. The mental image is booty fab but it works well. It is neatly wire-tied to the vertical bars that raises and lowers the headrest. I have sheepskin covers but I think you could run the wire down underneath the leather.

-B-
 
That is one i didn't think of. Did you just use a computer speaker or get nice "voice type." I have heard of a few people using the CPU speakers that most of us have a suplus of.
 
FYI regarding GAIN:

In talking with the guy at HRO in Portland he tells me that comet and diamond rate antenas in "dbi" which is not actual deciables of gain. Larson rates antenas in deciables. I don't know too much about this but he stated something like take-off 1.2 from the number on the Comet/Diamond units to get true gain numbers.

I'm sure an expert can clarify or correct here. Just wanted to relay what the salesperson said at the store.

To summarize: A Larson rated at 2.1 Db would be equal to a Diamond rated at 3.2Db.

It was "db" vs "dbi" as he stated. But they all list "Db" in marketing materials.
 
sprocket3 said:
That is one i didn't think of. Did you just use a computer speaker or get nice "voice type." I have heard of a few people using the CPU speakers that most of us have a suplus of.
Click to expand...

It was a speaker that I bought when I got the radio from one of the big online ham stores. Standard "made in China" inexpensive speaker;
approx 4 x 2 x 6

-B-
 
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I read about that somewhere. I can't recall how you figure DB from DBi but the site had that info. DBi ratings are much higher than DB ratings.
 
that is a good thing to know and keep in mind

I think I recall the diamond or Larsen site listing both ratings on some antennae
 
Last edited:
Sure is:

That's a huge difference between Larson and Diamond/Comet.

"Therefore, the gain of an antenna referenced to an isotropic radiator is the gain referenced to a half-wavelength dipole plus 2.15 dB:

dBi = dBd + 2.15"
 
Ok. Got it all mounted up and done! Looks great and sounds even better. Going to an external speaker makes a huge difference in sound quality.

I was working a repeater 60 miles away with 5 watts and the short 20" SBB2 antena while sitting in the garage. Very nice quality audio on Send/Rx. The sound quality is amazing. Like your in the same room at times.

I'll post some pics soon.
 
Here are some photos if they posts. Try the link if it doesn't work!

http://new.photos.yahoo.com/stewart1466/album/576460762404221482
DSCN2336.webp
DSCN2343.webp
DSCN2344.webp
 
Sprocket,

That looks like a really nice and clean install.
Congrats. Very nice.

Regards

Alvaro
 
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