10 meter mobile, 102 whip vs Larsen NMO 27 (or similar)

[mr_fx]

I am planning to add 10 to my mobile setup, however I am debating between just running a 102 whip on the back bumper, or the front fender... OR running a Larsen NMO-27-c or similar in the middle of the roof hard mounted

Th 102 would likely be somewhat directional, while the Larsen would be a little weak, but recoverfrom some of it's loss because of the healthy ground plane, that a hard mount NMO would offer

 

[W5LZ]

In general, I don't think there would be a 'large' difference between the two. Some differences, sure. But nothing 'drastic'. That "somewhat directional" isn't going to be noticeable in most cases, because that 'somewhat' just isn't much at all. I think that NMO hard mount would be better than a mag-mount. But, the "ground" for either will be about the same except for some very slight amount of 'directionality' from the positioning of the antennas. Of the two antennas, which would present the least 'practical' difficulties? The 'taller' of the two would be 'better', but also would hit the most things. Somewhere in there one will be more 'livable' than the other. Up to you...
- 'Doc

 

[northern35s]

102" on the roof, win win

The only real way to find out which would be better, test them both, I don't know what the NMO antenna is, but I'm very familiar with the 1/4WL vertical as I use one.

If you bumper mount the 102" then the currents in the car would be in opposition to the currents in the antenna, maximum current in the 1/4WL is at it's base, the vehicle's opposite currents in the body would cancel the high current at the antenna base, right up to the point the antenna is in the clear, dependent on the vehicle, that could be a significant amount of the antenna.

In the above example the roof mounted antenna could well be a much better performer as a result.

I remember reading a recent antenna shoot out article where all manner of mobile antennas were tested, some very expensive Scorpion and Hi Q screwdriver antennas, along with a myriad of others, they were all beaten by a pair of hamsticks, the reason? The hamsticks were the only antennas that weren't shrouded by the vehicle body, we have a $40 dollar antenna beating the best part of a $1,000 installation, I'd be a bit of a sore loser in that case :headbang

On the subject of directivity, I'd have said positioning of the antenna on a vehicle, at HF, would have little effect, however I have on a number of occassions found quite the opposite. A friend of mine was testing a recent home brew shortened mobile antenna for 10m mounted in the middle of his trunk, he was in the UK and I was on the Greek Island of Crete, together we were working stations from the US, so if you can imagine my friend was inbetween myself and the US stations, if he directed his car to me he came up 2 S points and went down the same amount with the US stations, if he did a 180 exactly the opposite happened.

2 S points on a calibfrated S meter is the equivalent of 12dB, that's 12dB directivity in his car, if someone was telling me the story I'd have said BS, but I was part of the experiment, I can hear you screaming BS now

 

[n0zna]

go whith the whip,you dont have to worry about anything but coax...73 de JW

 

[AudioShockwav]

Lol, I am not screaming BS, I just have seen enough S-meters and you and I both know that very few of them are anywhere near accurate, much less truly "calibrated"
Most of them get a quick twist along with the TX and RX chain and the radio gets thrown in the Box at the Factory.
Gain is Gain, but a real 12 DB is a tad unrealistic unless it was really piss poor in one direction.
Even after a few pints at a London Pub.
73
Jeff

 

[northern35s]

Lol, I am not screaming BS, I just have seen enough S-meters and you and I both know that very few of them are anywhere near accurate, much less truly "calibrated"
Most of them get a quick twist along with the TX and RX chain and the radio gets thrown in the Box at the Factory.
Gain is Gain, but a real 12 DB is a tad unrealistic unless it was really piss poor in one direction.
Even after a few pints at a London Pub.
73
Jeff

If it wasn't repeatable I'd have said magic fairy dust blew in the right direction, but I was based in Crete for a month and these figures were repeated on numerous occassions with numerous stations, not just myself. I agree about the S meters, that's why I introduced the term calibrated S meter in my original post, however if we were to halve the figure to 6dB it's still a significant value.

I know it's not possible and I still don't believe the car alone was responsible, for info where my friend was parked is next to the sea on a shallow estuary with a fast running tide, the difference between high and low water is probably in the region of 2 miles of beach, this probably had more to do with the results.

It's a favoured location for mobile and portable operations and I've tried to recreat the results with my own car and so far I haven't seen the same results, that said, 10m hasn't been anywhere near as good as it was in October 2011, an oustanding period of time for global 10m communication

As an aside, I've visited the High Sierras a number of time, and visiting Yosemite was a magical experience, but I suppose being an Ansell Adams devotee had something to do with that.

 

[Lil'Yeshua]

In general, I don't think there would be a 'large' difference between the two. Some differences, sure. But nothing 'drastic'. That "somewhat directional" isn't going to be noticeable in most cases, because that 'somewhat' just isn't much at all. I think that NMO hard mount would be better than a mag-mount. But, the "ground" for either will be about the same except for some very slight amount of 'directionality' from the positioning of the antennas. Of the two antennas, which would present the least 'practical' difficulties? The 'taller' of the two would be 'better', but also would hit the most things. Somewhere in there one will be more 'livable' than the other. Up to you...
- 'Doc

I used to run a 102" w/spring on a bumper chain mount on the right side of my fleet side bumper on my 81' Chevy 1/2 ton deluxe step side truck. It worked exceptionally well as the antenna because of the step side fenders being farther away from the antenna helped it get out. It was directional at extreme distances which was helpful when you wanted to talk to someone twenty miles away. The downfall to this is if you were driving away from your contact while talking.

 

[ghutch]

Any antenna shrouded by the auto sheet metal has a negative effect. Top center mount is best for most mobile antennas. Ck out K0BG.com

 

[W5LZ]

I think propagation had more to do with it than just the directionality of a mobile antenna. If not, you'd better patent that mobile antenna set up! There can be ~some~ directionality with a mobile antenna, but not really a lot. Which is exactly what I said in that other post above. You've seen it, I've seen it, I would think that most people have seen it at least a little. There certainly can be a big difference just from where you happen to be parked but it alone can't account for all of it. Especially at longer distances.
- 'Doc