Wide Band Ground Independent Dual Band Antenna

[Lscott]

I've been looking for a good dual band ground independent antenna for both the HAM 2M/70cm band and the MURS/GMRS bands.

 

I have a new Comet CA-2x4SR antenna, which works, but requires a good ground plane. I don't want to drill any holes and the coupling with a magnet mount results in higher SWR, but still usable.

 

I have an old Comet CA-2x4MB which is ground independent but hasn't been manufactured in years. I would like to find something like it.

 

I recently did some SWR scans using a Rigexpert AA-1000 antenna analyzer, got similar results with spot checking using an old MFJ-269 as a sanity check, to confirm the performance. The antenna is mounted on a luggage rack using a Diamond K550KM rack mount kit on a cross rail on top of a Jeep. 

 

The scans all look very good for a large high gain antenna.

[Lscott]

I can't seem to add any more files at the moment showing the scans for the Ham 2M and 70cm bands, which look just as good. The stated antenna gain is 4.5dbi from 145-148 and 7.7dbi from 440-450 with an SWR of less than 1.5, the graphs in the datasheet show over the above range a max SWR of 1.2. The antenna is about 59 inches in length, a big one.

[marcspaz]

I think you are going to be hard pressed to find a current production raidialess dual-band mobile antenna that will go all the way to 470 and be under 2:1 SWR. The Diamond NR73BNMO is probably the closest, but you're going to be looking at 2.5:1 at around 467. Maybe 2:1 at 462.

[Lscott]

I think you are going to be hard pressed to find a current production raidialess dual-band mobile antenna that will go all the way to 470 and be under 2:1 SWR. The Diamond NR73BNMO is probably the closest, but you're going to be looking at 2.5:1 at around 467. Maybe 2:1 at 462.

I'm sure you're right. This was the point of asking. I did send an email off to Diamond Antenna a few days ago asking if they even offer anything like the comet CA-2x4SR. Never got a reply to date.

 

I wish Comet still made the CA-2x4MB. The only failing was the spring for the fold over feature lost tension so the antenna would lift out of the socket then flip over at highway speeds. I had to wrap several layers of tape around that area to stop it. Other than that it's worked fine for years. I haven't had any issues with loose hardware, screws, or rust.

 

If anybody has any interest I have the AA-1000 SWR scans of the CA-2x4SR on the roof of my Jeep using a 5 inch magnet mount and inside the house using a home brewed mount with 4 drooping radial elements, which gave the lowest SWR scan curves, much better that the specs in the Comet datasheet. I was rather pleased to see that.

 

For the moment I can't seem to attach any files to upload. The message says I only have 666 bytes left. Not sure why it's still limiting me or is there a time limit that has to expire first before the upload limit is reset. 

[Lscott]

Just and update I got an email from Diamond Antenna this afternoon. They have a new product in the works. This was the info I was sent below in quotes.

 

"We will have the NR240A in a couple of months.  This antenna, when on a mag mount is 140MHz-170MHz and 430MHz-470MHz.  When it is grounded on a hatch/lip mount it is 140MHz-165MHz  and 440MHz-465MHz. "

 

Looks close to the spec's for the Comet wide band antenna. If the above is correct it seems the antenna is optimized for a wider bandwidth using a magnet mount? That is unless they got the magnet mount verses the hatch/lip mount bit swapped. Either way it looks like there will be an alternative antenna. I just wish it didn't require grounding. More new vehicles have plastic body panels so grounding gets harder to do.  

[marcspaz]

Good info.  Thanks for sharing!

[Radioguy7268]

I think there's confusion between an RF ground plane, and electrical grounding. 

 

For UHF/GMRS frequencies, a ground plane is required for best signal propagation when you're working with a 1/4 wave antenna. A longer 1/2 wave antenna does not normally require a ground plane. The ground plane is a counterpoise to the antenna's radiating element.  The counterpoise (RF ground plane) is going to reflect signals that would otherwise be radiated down by the antenna.

 

For plastic body vehicles - look for something like this to use as an RF ground plane: https://www.solidsignal.com/pview.asp?p=K332 - or just use a 1/2 wave antenna.

 

The DC ground for a vehicular antenna is provided by the coaxial shielding braid. That's going to measure continuity to vehicle ground no matter what type of plastic you're mounting the antenna to... provided the radio chassis itself is actually grounded. 

 

I realize I'm being simplistic. That's where we need to start from when someone wants to "ground" their antenna.

[Lscott]

I think there's confusion between an RF ground plane, and electrical grounding. 

 

For UHF/GMRS frequencies, a ground plane is required for best signal propagation when you're working with a 1/4 wave antenna. A longer 1/2 wave antenna does not normally require a ground plane. The ground plane is a counterpoise to the antenna's radiating element.  The counterpoise (RF ground plane) is going to reflect signals that would otherwise be radiated down by the antenna.

 

For plastic body vehicles - look for something like this to use as an RF ground plane: https://www.solidsignal.com/pview.asp?p=K332 - or just use a 1/2 wave antenna.

 

The DC ground for a vehicular antenna is provided by the coaxial shielding braid. That's going to measure continuity to vehicle ground no matter what type of plastic you're mounting the antenna to... provided the radio chassis itself is actually grounded. 

 

I realize I'm being simplistic. That's where we need to start from when someone wants to "ground" their antenna.

 

Yes some people do get it confused. What I'm looking for is the equivalent of a 1/2 wave antenna, thus no ground plane is normally required. The Comet CA-2x4SR does require a ground plane as I suspected from my testing. I confirmed this the other day by contacting Comet tech support. The reply I got is quoted below.

 

"The CA-2x4SR is a 5/8 wave, so yes it must have a ground plane underneath the antenna in order to work properly.

 

It was designed to be installed on sheet metal, like a vehicle trunk deck, hood, or even hatch back door.

 

You need about 20” radius of metal under the antenna, but rarely is it possible to create a ground plane that provides the impedance needed at the antenna feed point.

 

If you can use one of our lip mounts attached to the door edge, or hood edge to provide the ground plane."

 

From my SWR scans you do need a really good ground plane. A magnet mount sort of works but a good direct electrical connection to a ground plane, or set of correctly cut to length radials, works even better from what I see.

[kogar]

ok, first: Apologies for resurrecting this thread, but it's relevant for me.  I am hooking up ham (Kenwood TM-D710GA) and GMRS (Midland) radios in my Jeep Wrangler JL.  I had originally fabbed some 12ga steel antenna mounts, but didn't get the chance to finish wiring them and check SWR.  Instead, I purchased a Comet CA-2X4SR and a Comet CP-5M lip mount.  Frankly, I think the Comet lip mount has a nicer look and feel than my cheezy sheet metal bendy-hack does. I haven't wired the antennas up yet though, but this thread makes me a bit nervous.  

 

For those of you that don't know much about the new Wranglers, let me explain: Most of the exterior is aluminum body panels.  Since I often ride "topless" in the summer, a mount on my hardtop roof is a non-starter.  That means I mount my antennas in the rear or in the front.  The best place for my needs is probably midpoint along the hood.  However, based on this thread, it seems like the Comet lip-mount won't yield sufficient ground plane for UHF.  This puzzles me a bit, because I thought the 5/8 wouldn't have need of a ground plane like a 1/4 wave would.

 

Am I making a bad decision by using the Comet lip mount?  Should I go back to my fabbed sheet metal plates that bolt into the steel engine bay? (just underneath the hood - similar to this mount that you can use on a JK model: https://www.amazon.com/dp/B00IHMZT1S )

[marcspaz]

I have a 2016 JK. I am using the comet NMO mount and the comet CA-2x4SRNMO, clamped to the side lip of my hood, on the passenger side, just in front of the windshield. It works great. 1.5:1 swr on 467 mhz.

 

I'll post a pic tomorrow.

[kogar]

Thx marc. I’ll take 1.5 on 467 if I can get it. The ground plane talk just puzzles me for a 5/8, but it’s been a LONG TIME since I did antenna-nerd stuff. 

[Downs]

I use an l bracket in the hood channel of my Jeep XJ. My goto is typically a Commet SSB5 which is 1/2 wave on 2m and 2x 5/8 on 70cm. SWR across the board for HAM and GMRS is sub 1.7 MURS is 2.1 or so. Ive got a commet SS680 thats a little shorter that i get similar performance out of

 

If i know im going to be running nothing but UHF for doing something like a trail ride Ill switch my my cheap little Tram 1181. Its sub 1.8 on 70cm and GMRS even on the fender. Does about 2.0 on 2m and a little more on MURS.

 

Next time i have my headliner out i think I'm going to punch the roof for a NMO up top but the performance on the fender with these antennas has been very satisfactory for my uses.

 

 

Sent from my SM-G892A using Tapatalk

[marcspaz]

Comet mount and antenna for daily use.

 

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Antenna_1.jpg

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Antenna_2.jpg

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_under_hood.jpg

 

 

 

Comet mount with Tram antenna for offroad use (so I don't break the other antenna).

 

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Tram_Antenna_.jpg

[kogar]

Thanks! That looks like what I plan to do! I got springs for mine though, so I should be ok. I have a midland 1/2 wave and a Tram tri bander that I can sub out if things get really bad. 
 

psst... i don’t use a hi-lift. Im a huge proponent of the x-jack! https://www.arb.com.au/recovery/x-jack/

[RCM]

I just drilled a hole in the hood of my JK and added an NMO mount. I'm using a simple 1/4 wave antenna.

 

I've been using farm/ sheepherder's/ high lift (Hi-Lift is a brand name; lots of other companies have made them) jacks for at least 40 years. It is a true multi-tool; a jack of all trades even (couldn't resist!)

Those exhaust jacks are nothing new either. They are a great invention, but the farm jack can do a lot of things an exhaust jack cannot.

 

I like your Chevy truck, Marc. I have the military version of that. They came with a 6.2 diesel, TH400, full floater 14 bolt rear with Detroit Locker, Dana 60 front, 4.56 gears. All as standard equipment.

[marcspaz]

I just drilled a hole in the hood of my JK and added an NMO mount. I'm using a simple 1/4 wave antenna.

 

I wanted to do that, but my wife complained that she didn't want to see the antenna in the middle of her field of view.  Figured that was a nice compromise.  LOL

 

I've been using farm/ sheepherder's/ high lift (Hi-Lift is a brand name; lots of other companies have made them) jacks for at least 40 years. It is a true multi-tool; a jack of all trades even (couldn't resist!)

Those exhaust jacks are nothing new either. They are a great invention, but the farm jack can do a lot of things an exhaust jack cannot.

 

I love my farm jack.  I agree, they are a get multipurpose tool.  I like the air jacks but my Jeep is too tall.  I can't find one that actually gets the tires off the ground.

 

I like your Chevy truck, Marc. I have the military version of that. They came with a 6.2 diesel, TH400, full floater 14 bolt rear with Detroit Locker, Dana 60 front, 4.56 gears. All as standard equipment.

 

Thanks!  I know it doesn't look like it now, but that is/was an M1008 CUCV.  At least it was when we bought it.  It started life on Fort Lee, and eventually made its way here.

 

We completely restored it to original military spec, including the troop seats and paint.  The original 6.2 was in it and it only had 52,000 on the clock.  It had the IR/Service lights, 24v electrical (basically for just the starter and jump port).

 

Sadly, the motor let go, then the TH400 let go and took out the transfer case.  After that, someone smacked the bed with a big truck and made a mess of it.

 

We put a 6" lift kit on it, cross-over steering, high-performance carbed 350, rebuilt the turbo 400 with a manual reverse valve body, and slapped a new transfer case in it.  It has all new brakes.  Its about to get a new hydro-assist, front and rear winch, and some other minor stuff.

 

Anyway, we changed it so much that we decided its not much of a M1008 any more.  So we are restoring the full interior and we are going to slowly rehab the outside.

 

After the first restore...

 

http://fiveguysracing.com/marc/CUCV/CUCV1.jpg

 

http://fiveguysracing.com/marc/CUCV/CUCV2.jpg

 

 

 

 

I volunteer with the County, doing emergency comms.  So, we are setting it up for 'Hi-Visibility'. We still need to finish the paint, but this is what it looks like right now...

 

 

 

http://fiveguysracing.com/marc/CUCV/CUCV3.jpg

 

http://fiveguysracing.com/marc/CUCV/CUCV4.jpg

[kogar]

Nice work on the restore, Marc!  Ive always been envious of people that can do such amazing things for vehicles.

 

re: hi-lift - I’m not knocking all the great utilities those things have, but I’ve seen them darn near kill a couple people because they were inexperienced. My arb xjack will give my lifted wrangler the clearance it needs. In my case, Im more likely to need to get my jeep up in sandy beaches or mud, so a large exhaust lift is a better option for me. We can probably agree the best solution is to have both 

 

im hoping to find a friend tomorrow who will help me rewire my radio. Then I’ll let y’all know what I get with the swr. 

[marcspaz]

Nice work on the restore, Marc!  Ive always been envious of people that can do such amazing things for vehicles.

 

Thanks!  I appreciate it!.  Yea, it take a lot of time and money to restore these old vehicles.  But, so worth it when they are done.  That old CUCV is my favorite vehicle to drive.  I miss that old 6.2L Detroit, but the 350 is pretty fun too. 

 

 

re: hi-lift - I’m not knocking all the great utilities those things have, but I’ve seen them darn near kill a couple people because they were inexperienced. My arb xjack will give my lifted wrangler the clearance it needs. In my case, Im more likely to need to get my jeep up in sandy beaches or mud, so a large exhaust lift is a better option for me. We can probably agree the best solution is to have both 

 

No joke, right there... You can kill yourself quick with a farm jack.  The bags are awesome for mud, snow and sand, for sure.  Definitely very stable platform.

 

 

im hoping to find a friend tomorrow who will help me rewire my radio. Then I’ll let y’all know what I get with the swr. 

 

Cool.  Let us know.  It's always good to see how others resolve issues.  Things we share will likely save someone a lot of grief. 

[RCM]

I wanted to do that, but my wife complained that she didn't want to see the antenna in the middle of her field of view.  Figured that was a nice compromise.  LOL

 

 

I love my farm jack.  I agree, they are a get multipurpose tool.  I like the air jacks but my Jeep is too tall.  I can't find one that actually gets the tires off the ground.

 

 

Thanks!  I know it doesn't look like it now, but that is/was an M1008 CUCV.  At least it was when we bought it.  It started life on Fort Lee, and eventually made its way here.

 

We completely restored it to original military spec, including the troop seats and paint.  The original 6.2 was in it and it only had 52,000 on the clock.  It had the IR/Service lights, 24v electrical (basically for just the starter and jump port).

 

Sadly, the motor let go, then the TH400 let go and took out the transfer case.  After that, someone smacked the bed with a big truck and made a mess of it.

 

We put a 6" lift kit on it, cross-over steering, high-performance carbed 350, rebuilt the turbo 400 with a manual reverse valve body, and slapped a new transfer case in it.  It has all new brakes.  Its about to get a new hydro-assist, front and rear winch, and some other minor stuff.

 

Anyway, we changed it so much that we decided its not much of a M1008 any more.  So we are restoring the full interior and we are going to slowly rehab the outside.

 

Nice! I love the CUCV pickups. One of my friends has an M1028A1 which is the dually pickup version, Dana 70 rear (still with Detroit Locker), NP205 'case. I would like to build something like an M1028, but with a crew cab and a bobbed bed. I've seen a picture of one done like that, and it was sweet!

[RCM]

Nice work on the restore, Marc!  Ive always been envious of people that can do such amazing things for vehicles.

 

re: hi-lift - I’m not knocking all the great utilities those things have, but I’ve seen them darn near kill a couple people because they were inexperienced. My arb xjack will give my lifted wrangler the clearance it needs. In my case, Im more likely to need to get my jeep up in sandy beaches or mud, so a large exhaust lift is a better option for me. We can probably agree the best solution is to have both 

 

im hoping to find a friend tomorrow who will help me rewire my radio. Then I’ll let y’all know what I get with the swr. 

You're absolutely right about the danger. Besides the instability, if you run them dry they have a tendency to suddenly drop the vehicle on you while whacking you upside the head with the handle! I learned that as a teenager when one dropped a Massey Ferguson tractor and whacked me right in the chin. After that I learned to always have a can of oil and dribble a bit in the workings before attempting to use it.

[kogar]

Got antenna 1 wired up easy-peasy!  SWR shows 1.2ish.  I'll take that

 

[Downs]

Got antenna 1 wired up easy-peasy! SWR shows 1.2ish. I'll take that

 

Wheres the antenna mounted?

 

Sent from my SM-G892A using Tapatalk