2M antenna with 3/8-24 threaded base

[KC5MNG]

Can someone point me to a mobile 2M or dual band antenna that will screw into a 3/8-24 threaded base? Thanks

[KE4VVF]

Hustler CG-144 - http://www.hamradio.com/detail.cfm?pid=H0-003363

New-Tronics (Hustler) has others listed at - http://www.new-tronics.com/main/html/products.html

[KC5MNG]

What about a dual band with the 3/8-24 mount? I had a dual band Yaesu radio years ago and would like to have another, but there's no sense spending the extra $$$ if I can use the 70cm band

[WB6BYU]

One problem is that most 3/8-24 mounts aren't designed for VHF/UHF operation, where
an inch or two of bracket between the coax shield and the car chassis can throw the
antenna resonance out of band.  Also, the 3/8-24 mount only allows the antenna to
connect to the center conductor of the coax, and many matching networks (as are
often needed for dual-band antennas) require a ground connection as well.

Besides, how many hams want their VHF/UHF antenna mounted on the bumper, trailer
hitch, or wherever their HF antenna goes?

That's why VHF/UHF antennas generally come in a different mounting style, such as
the NMO, that is designed to go in a flat roof and provide connection to both sides
of the coax.


But if you want to try a 2m or dual-band antenna in your mount, I've made my own
by using a 3/8-24 set screw and soldering a piece of brass brazing rod into the hex
hole in the head.  You could do the same with the radiator from some simple dual-band
antennas, the type that are a bit shorter than 1/4 wave on 2m with a loading coil of
5 turns or so in the lower half of the element.  A more elaborate installation might use
a longer 3/8-24 bolt with a hole drilled down the middle and a set screw, but many
bolts with fine pitch threads are Grade 5 or better, and drilling such a hole might
not be easy.

[WB2WIK]

What Dale said is right.

You normally won't find dual-band or any 440 MHz antennas with 3/8-24 mounts because that mount does not function properly at such a high frequency; it "barely" works at 146 MHz.

The industry standard is "NMO," developed by Motorola and Larsen, for VHF-UHF work.  3/8-24 works fine at lower frequencies (typically below 54 MHz).

[AC4RD]

I bought a 3/8x24 2m/440 quarterwave from Buxcomm (www.packetradio if I remember right) a few months back, $7 or so.  And I got another couple of his 2m 3/8x23 singlebands--at $5 it's great to have a spare or two on hand.

I like 3/8x24; I've got 3 mounts on my car right now, and it's easy to swap antennas when they all have the same mount.  Lots of people are telling you they don't work for VHF/UHF, but I have no trouble getting into repeaters 25 miles away on 440 with my 706 set at 30% power.   So I've got no complaints, not a bit!

[KB4QAA]

3/8-24 mounts are so troublesome that I have used them for over 25 years on 2m/70cm! 

I am in the process of getting ready to drill holes in my car (gasp) and try out NMO mounting though for a sleeker installation.

[AC4RD]

the 3/8-24 mount only allows the antenna to
connect to the center conductor of the coax, ...
Besides, how many hams want their VHF/UHF antenna mounted on the bumper, trailer
hitch, or wherever their HF antenna goes?

Two additional points:  "only allows the antenna to connect to the center conductor" -- this may refer to some specific 3/8x24 setup WB6BYU saw.  My own 3/8x24 mounts on my car are all electrically bonded from the shield side of the connector to the car body--that's actually critical for good HF performance IMO.   And "mounted on the bumper"--I've got two 3/8x24 mounts at bumper and tailgate level, for HF and 6m, and one on my roofline, for the 2m/440 antenna.  As I said, this works great for me, YMMV.

[WB6BYU]

Two additional points:  "only allows the antenna to connect to the center conductor" -- this may refer to some specific 3/8x24 setup WB6BYU saw.  My own 3/8x24 mounts on my car are all electrically bonded from the shield side of the connector to the car body--that's actually critical for good HF performance IMO. 

That's not what I meant.  The good ground connection should go without saying.
It's the connection to the antenna that is one-sided.  You can't make a parallel
tuned network with one side grounded as part of the matching network on the antenna
if you don't have anything ground connection on the antenna.

By contrast an NMO provides both coax center and ground to the antenna, so you can
put a tapped matching network on the base of your antenna.  That's often what you
need for a dual-band antenna, at least if you want to maintain a reasonable radiation
pattern.

[AC4RD]

The good ground connection should go without saying.
It's the connection to the antenna that is one-sided.  You can't make a parallel
tuned network with one side grounded as part of the matching network on the antenna
if you don't have anything ground connection on the antenna.

Once again I'm obviously misunderstanding your point.  I haven't found it necessary for the 2m/440 one at my roofline, but my 3/8x24 HF mounts usually have either a capacitor or a small coil at the base--between the antenna feedpoint and the body of the mount, which is bonded to the car body--for matching, so I get a nice neat 50-ohm load. 

[W4KVW]

Several companies make an adapter that goes from an NMO to 3/8th mount but NONE that I know of that go the other way around! 

Clayton
W4KVW

[WB6BYU]

Once again I'm obviously misunderstanding your point.  I haven't found it necessary for the 2m/440 one at my roofline, but my 3/8x24 HF mounts usually have either a capacitor or a small coil at the base... 

Exactly:  between the antenna and ground.  You have to put that across the mount,
meaning that you can't just swap antennas for different bands on that mount without
also changing the shunt element.  (Though you might have a value that works for a couple
adjacent bands.)

You can put a quarter wave (or some variants) on a 3/8-24 mount because it only requires
one connection:  to the center of the coax.  But if you want a base where you can switch
between, say, 1/4 or 1/2 wave antennas for the same or different bands, you run into a
problem because the 1/2 wave antenna requires a ground connection for the matching
network, and there is no ground available on the antenna side of the mount.

Most commercial VHF/UHF antennas that are longer than 1/4 wavelength require a ground
connection for the matching network.  (You can argue about the 5/8 wave, where lengths
that can be matched with just a series coil and low SWR have less than optimum gain.)
This is particularly true of multi-band antennas.  That's why the range of options for the
3/8-24 mount is limited.  The NMO mount (or the SO-238 style) provide a ground connection
in addition to the coax center conductor, so you can build any required matching into the
antenna rather than requiring a particular value to be wired into the base when you swap
antennas.

Several companies make an adapter that goes from an NMO to 3/8th mount but NONE that I know of that go the other way around! 

And this is exactly the reason:  The 3/8-24 is a single wire connection to the center of
the coax.  The NMO is a two wire connection to the center and shield of the coax.

You can't convert from a 3/8-24 to an NMO unless you have some way to run the ground
connection to the NMO mount.

[AC4RD]

  You have to put that across the mount,
meaning that you can't just swap antennas for different bands on that mount without
also changing the shunt element.  (Though you might have a value that works for a couple
adjacent bands.)

You can put a quarter wave (or some variants) on a 3/8-24 mount because it only requires
one connection:  to the center of the coax.  But if you want a base where you can switch
between, say, 1/4 or 1/2 wave antennas for the same or different bands,

I'm not trying to be a problem, you're a nice guy and you are extremely helpful here on eham.  But I'm really not getting this.  I have a shunt coil between the feed point on a 3/8x24 mount, and it works great on 20m, 17m, and 15m, with a DXE 54" mast and a pre-tuned Hustler resonator and a homebrew cap hat. I tune my antennas for resonance, and then use a coil or a capacitor across the base of the mount to get a nice 50ohm match.  Works GREAT.

OK, I can't quickly switch from quarter-wave to half-wave without changing the shunt.  Why in the world would I WANT to switch from a quarter-wave to a putative half-wave on 17 meters for mobile operation?

The basic 3/8x24 mount works just dandy for 99% of people, and you can complain that it doesn't meet some idealistic model, but for most of us using them, they work GREAT and they're versatile.   You don't like them, OK, no problem.  But when you tell people they don't work, that's just not true.  Mine work great on multiple bands and I've been using them for 15 years without problems. 

[WB6BYU]

The point was not that 3/8-24 mounts don't work on HF:  they do.  But at VHF/UHF many
antennas (especially those with gain over a quarter wave) require some sort of matching
network at the base that needs a ground connection.

At HF or 6m, few hams use mobile antennas that are much longer than about 1/4 wavelength,
and you can match that with a series element without needing a ground (except for the shunt
matching element.)

But hams DO use half wave, or 2 x 5/8 wave antennas, or many other designs, on VHF/UHF,
and that is where the NMO makes these possible because it provides a ground connection
for the required matching networks.

And, getting back to the original question, that's why there are very few dual-band antennas
built for a 3/8-24 mount, and those that are will rarely be more than 1/4 wavelength on 2m.

[W8JX]

The point was not that 3/8-24 mounts don't work on HF:  they do.  But at VHF/UHF many antennas (especially those with gain over a quarter wave) require some sort of matching network at the base that needs a ground connection.

Well a single 5/8 wave does not need a base match other than a coil and I used a Hustler mobile collinear for 2m for many years on a bumper mount with a 3/8 x 24 stud. It was 5/8 over 1/4 and worked quite well.