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eHam Forums => Mobile Ham => Topic started by: KC5MNG on January 18, 2013, 08:19:45 PM



Title: 2M antenna with 3/8-24 threaded base
Post by: KC5MNG on January 18, 2013, 08:19:45 PM
Can someone point me to a mobile 2M or dual band antenna that will screw into a 3/8-24 threaded base? Thanks


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KE4VVF on January 18, 2013, 09:53:42 PM
Hustler CG-144 - http://www.hamradio.com/detail.cfm?pid=H0-003363 (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 (http://www.new-tronics.com/main/html/products.html)


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KC5MNG on January 19, 2013, 09:43:38 AM
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


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: WB6BYU on January 19, 2013, 11:53:37 AM
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.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: WB2WIK on January 19, 2013, 05:53:57 PM
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).


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: AC4RD on January 20, 2013, 05:51:53 AM
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!


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KB4QAA on January 21, 2013, 07:10:39 PM
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.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: AC4RD on January 26, 2013, 05:11:37 AM
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.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: WB6BYU on January 28, 2013, 03:51:39 PM
Quote from: AC4RD

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.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: AC4RD on January 29, 2013, 03:46:26 AM
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. 


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: W4KVW on January 29, 2013, 01:18:22 PM
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


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: WB6BYU on January 29, 2013, 04:06:07 PM
Quote from: AC4RD

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.


Quote from: 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!  ???



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.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: AC4RD on January 29, 2013, 05:07:08 PM
  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. 


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: WB6BYU on January 29, 2013, 05:27:01 PM
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.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: W8JX on January 29, 2013, 06:03:40 PM
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. 


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KB3HG on January 29, 2013, 07:02:42 PM
I also have a 2m co-linear with 3/8-24 thread. I picked it up at a ham fest back in the 70s. works fine at the bumper mount even better on the rear deck. but its about 6 feet long. The swr was good and as an odd quirk would work on 11 meters. I was told that when I bought it at the ham fest. Strangely it worked on 11m. Still have it, have not used it in years. but its a different antenna. I don't even remember what brand it is, Cushcraft or Hustler?  Now I have NMO or 5mm mounts that I cobble together.

Tom Kb3hg


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: AC4RD on January 30, 2013, 09:10:18 AM
At HF or 6m, few hams use mobile antennas that are much longer than about 1/4 wavelength,
and you can match that with ...
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.

OK, I've got your point; I've been misunderstanding what you were getting at.  Sorry!

You're right, I've never bothered with anything other than a simple quarter-wave for VHF or UHF. 


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KC9Q on February 03, 2013, 04:26:43 AM
If you don't care about antenna gain, then you can use a 1/4 wave 2M whip.  A 1/4 wave at 2M is about a 3/4 wave at UHF which will give you dual band operation.  Similar principal as a 5/8 wave (3 dB) 2M whip can also be used as a 1/4 wave whip for 6M.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KJ4YOJ on March 11, 2013, 05:12:18 PM
I use a Hustler SF-2.  It's cheap, but it requires tuning.  It works great on 2M, and I even tuned it up on 10M once and worked Canada with it (from Nashville, TN)  http://www.universal-radio.com/catalog/hamantm/1999.html


73,
Paul KJ4YOJ


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: KG6YSF on March 11, 2013, 10:11:02 PM
Firestik makes both quarter wave and five-eighths wave fiberglass whips. They look just like their 11m antennas. I have been looking at them for the 2m in my Jeep. I abuse it at least monthly so I want something simple and robust. Granted it is just a 2m not dual band. The quarter wave with a stainless spring and ball mount is what I will probably use. and it will match the 11m that way.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: M6GOM on March 17, 2013, 06:25:23 AM
If you don't care about antenna gain, then you can use a 1/4 wave 2M whip.

The difference in gain of any mobile vertical antenna over another is so low as to make it almost worthless installing them over a simple 1/4 wave antenna. Because we mostly use repeaters on VHF/UHF mobile the elevation pattern of a 5/8 wave or longer is actually detrimental in a lot of areas.

Certainly my own extensive A/B testing between a 1/4 wave and 5/8 wave monoband 2m antenna has found no discernable difference to a repeater up to a distance of 55 miles away either on the S meter or RX audio strength and I've talked through that repeater with the 1/4 wave with just 10W. Simplex on flat land I've not noticed any difference over a 25 mile distance.


Title: RE: 2M antenna with 3/8-24 threaded base
Post by: K1DA on May 28, 2014, 06:14:59 PM
How does an antenna affect received audio strength on a FM receiver with a limiter.  Once you hit full quieting
you can quintuple the signal level and not notice a difference.  Good Fm receivers will mantain audio level until just before the squelch closes on a weak signal.