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Author Topic: Larsen nmo 150 5/8ths wave and 440  (Read 5812 times)
KJ4OBR
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Posts: 104




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« on: June 20, 2011, 01:07:04 PM »

I'm pretty sure I know the answer to this one, but I'm gonna ask it anyway Wink (Flame On!).

Lets say I want to run the Larsen 150 5/8ths wave with my FT8900 to cover 2m and 6m (@K0BG: I know, I know, the 6m match would be a compromise, I just want to be able to hit the local 6m fm repeater.. for the sake of the thought exercise stay with me). What would that look like on 70cm? I assume it won't work but am hoping to be proven wrong.

If I'm right my next question is: Is there a 5/8ths wave on 2m / 440 dual band antenna out there? I'm pretty sure the Larsen 2/70  is a half wave and will not work as a 6m 1/4 wave so what other options might there be.

I have considered a duplexer and a dedicated 440 antenna, but this would put 3 antennas and 2 duplexers in the mix. (I currently use a CF-360 to split the Larsen 27 nmo cut for 10m away from a 6/2/440 triband that I'm only marginally pleased with)

Thanks!

73

Dave
« Last Edit: June 20, 2011, 02:37:23 PM by KJ4OBR » Logged
K0BG
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Posts: 9879


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« Reply #1 on: June 21, 2011, 06:01:28 AM »

I've never tried using a Larsen 2/70 as a 6 meter antenna. Since the base coil is tapped, I'd doubt it would work. You could use an antenna analyzer to check to see what it looks like.

There are companies making tri and quad band antennas which cover the the basic VHF/UHF bands. Most are Pacific rim companies, and even though they have a loyal following, the truth is they aren't nearly as rugged as the Larsen. And, they don't have any more gain, although you'd think so from the literature.

What I'd do is mount a Larsen NMO50, in addition to the NMO2/70, and use a diplexer to mix them.
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VA3WXM
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Posts: 277




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« Reply #2 on: June 21, 2011, 08:50:51 AM »

I've swept a Larsen NMO2/70 with a MFJ-259 just for the heck of it and, as you'd expect, it won't work on 6M.

As Alan has said, these multi-multi-band antennas seem to come from the Far East.  I had a Maldal EX-510 for a period of time.  It covered 6, 2 and 440.  It was extremely sensitive with respect to ground/counterpoise.  If it wasn't properly grounded, it tended to be quite deaf on VHF.

To make them work on multiple bands the manufacturer has to play electrical games with the matching section, antenna length, etc.  They're quite sensitive to the environment they're in and can be a bear to tune properly.

I personally run separate Larsen antennas for the bands I use: NMO27 for 10/11, NMO50 for 6, NMO150HW for 2 and NMOQ for 440.
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WB6BYU
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Posts: 13339




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« Reply #3 on: June 21, 2011, 09:47:11 AM »

I've done just that.  I can't check the SWR on 440, but it was adequate to hit the local
repeater on 5 watts.  The pattern isn't optimum and the match may be poor, but it
did radiate some signal.  (The Larsen glass-mount was better until the radiator got into
a battle with a passing tree branch.)

The good news is that, with the typical coax on a typical mount, the SWR won't be too
bad at the radio even if the antenna isn't a good match.  With 20' of RG-58, it won't
get much over 3 : 1 on 440 even with no antenna at all.  So the chance of damaging
your rig is relatively low.  I still wouldn't use it regularly at high power.


Is it optimum?  Certainly not.   Is it adequate for occasional local use?  It might be.
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KI4SDY
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Posts: 1452




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« Reply #4 on: June 21, 2011, 07:48:26 PM »

Let us know when you have burned up the transmitter and need suggestions on a new rig!  Grin

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ZENKI
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Posts: 960




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« Reply #5 on: June 22, 2011, 04:24:37 AM »

This antenna makes a good HF antenna as well, seriously.

See the ARRL Antenna Compendium  Vol 7, article by K2PEY.

I built this all band HF antenna using the LArsen NMO. hey it work. I have worked DX on from 40 through to 10 meters with it. Its calculated efficiency is from 2% to 65% from 40 meters through to 10 meters.

When I turn up to the hamfests as I work some ham buddies on the way, most ask where my HF antenna is! K0BG, wont be impressed and he will call it a dummy load. But hey its something interesting and new that did I did not buy as a dummy load! Its just a very interesting technical concept and challenge

Who else can work 40 meters with a 2 meter whip! Go read the article!
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K3GM
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Posts: 1816




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« Reply #6 on: June 22, 2011, 04:29:45 AM »

If you're interested in running separate antennas for the FT-8900, here's how to do it:
-Output of the FT-8900 and run it to the input of a Diamond MX-610 Diplexer.
This diplexer has 2 outputs, 1.3-30MHz and 49-470MHz. Attach your 10m antenna to the proper
port of this diplexer.

-Attach the 49-470MHz port of the MX-610 to the input of a Comet CFX-514J Triplexer. This
triplexer has outputs for 6m,2m, and 70cm.

The outputs of this triplexer are SO-239's so you can plug the PL-259's from the
antenna mounts directly into the triplexer eliminating any lossy gender
changers. The only jumper you'll need is from the FT-8900 to the input of the
MX-610.

As far as I know, there is only one mobile triband antenna available presently, and that's the Diamond CR-627B.  I own this antenna and was intending on replacing my old M911 tribander. The problem with the CR-627 is it's made from heavy duty spring steel and is very robust. You'd think this would be a good thing, except my antennas are NMO mounted in the roof of my 2007 Tahoe. There is no doubt in my mind that a low hanging branch would tear the mount right out of the sheet metal with this antenna installed on a vehicle's roof.  . The M911 is much lighter and yields to the branches.  I've used the same M911 for over 7 years, and although it continues to work fine, I'm punching 2 more holes in the Tahoe's roof and going with four  separate Larsen's.
« Last Edit: June 22, 2011, 04:36:53 AM by K3GM » Logged
KJ4OBR
Member

Posts: 104




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« Reply #7 on: June 22, 2011, 04:16:42 PM »

I'm currently running the EX-510 and I'm trying to move away from it because, contrary to your experience and everything I read I can't get an acceptable SWR if the antenna is grounded! I checked using a different 2/440 antenna to rule out the rest of the install and all is well. But if I insulate the mount from ground the Maldol is happy 1.3:1 or better which is how I've been running it prior to getting the 10m antenna. When I add the Larsen 27 (that needs a good ground and the duplexer) the Maldol SWR goes to 4:1 and up on 2 and 6. Hence the thought exercise presented..



I've swept a Larsen NMO2/70 with a MFJ-259 just for the heck of it and, as you'd expect, it won't work on 6M.

As Alan has said, these multi-multi-band antennas seem to come from the Far East.  I had a Maldal EX-510 for a period of time.  It covered 6, 2 and 440.  It was extremely sensitive with respect to ground/counterpoise.  If it wasn't properly grounded, it tended to be quite deaf on VHF.

To make them work on multiple bands the manufacturer has to play electrical games with the matching section, antenna length, etc.  They're quite sensitive to the environment they're in and can be a bear to tune properly.

I personally run separate Larsen antennas for the bands I use: NMO27 for 10/11, NMO50 for 6, NMO150HW for 2 and NMOQ for 440.
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KJ4OBR
Member

Posts: 104




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« Reply #8 on: June 22, 2011, 04:19:06 PM »

Yeah, thanks for that constructive contribution.


Let us know when you have burned up the transmitter and need suggestions on a new rig!  Grin


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KJ4OBR
Member

Posts: 104




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« Reply #9 on: June 22, 2011, 04:43:27 PM »

Good suggestion, but that leaves me without a 10m solution.




What I'd do is mount a Larsen NMO50, in addition to the NMO2/70, and use a diplexer to mix them.
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KJ4OBR
Member

Posts: 104




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« Reply #10 on: June 22, 2011, 04:44:08 PM »

It would be fun to get a meter on the 5/8 wave Larsen @440 and see what it looks like officially. I split time almost equally between 2m and 440 so need something for both that I don't have to worry about. I use 6 and 10 less frequently, but enough to want something that works.


I've done just that.  I can't check the SWR on 440, but it was adequate to hit the local
repeater on 5 watts.  The pattern isn't optimum and the match may be poor, but it
did radiate some signal.  (The Larsen glass-mount was better until the radiator got into
a battle with a passing tree branch.)

The good news is that, with the typical coax on a typical mount, the SWR won't be too
bad at the radio even if the antenna isn't a good match.  With 20' of RG-58, it won't
get much over 3 : 1 on 440 even with no antenna at all.  So the chance of damaging
your rig is relatively low.  I still wouldn't use it regularly at high power.


Is it optimum?  Certainly not.   Is it adequate for occasional local use?  It might be.
« Last Edit: June 22, 2011, 04:53:20 PM by KJ4OBR » Logged
KI4SDY
Member

Posts: 1452




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« Reply #11 on: June 23, 2011, 01:51:45 AM »

"Yeah, thanks for that constructive contribution."

Just stating the inevitable from my experience and that of many other hams who used defective antennas or antennas that were not designed for the frequency with high SWR. Transmitter protection circuits do not always work and can fail. Your radio may be headed for the junk yard!  Cry
« Last Edit: June 23, 2011, 02:47:31 AM by KI4SDY » Logged
K3GM
Member

Posts: 1816




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« Reply #12 on: June 23, 2011, 04:20:56 AM »

....Transmitter protection circuits do not always work and can fail......
So what you're saying is there are times when the fold back circuit functions as it should, and there are other times it decides not to, and sometimes it just fails......?  Why would this occur.....?

I have a question for you: Do you know the answer to the original question? (the first post, Vern....)
« Last Edit: June 23, 2011, 07:24:29 AM by K3GM » Logged
KJ4OBR
Member

Posts: 104




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« Reply #13 on: June 23, 2011, 07:14:26 AM »

 Roll Eyes Again, "Yeah, thanks for that constructive contribution." I'm not "DOING" it, I'm asking questions to learn and explore an option that on the first pass seems to be a possible solution to solve a problem. In the original post I thought I made it clear that this was a "thought exercise".  Sorry that you missed that.


"Yeah, thanks for that constructive contribution."

Just stating the inevitable from my experience and that of many other hams who used defective antennas or antennas that were not designed for the frequency with high SWR. Transmitter protection circuits do not always work and can fail. Your radio may be headed for the junk yard!  Cry
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K1CJS
Member

Posts: 6045




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« Reply #14 on: June 23, 2011, 07:30:46 AM »

It certainly WOULD help if people opened their eyes and read the thread before they open their pie hole and shove their foot it in.  Particularly those who think they know everything and have the tendency to offer what they think are witty remarks (constructive criticism) to others.

I don't know the answer to the original question, but I think it is something that could be looked at creatively, even if ultimately it wouldn't work.
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