RF leakage from a NMO mount and coax cable?

[btu44]

Hello all,

Hope you guys don't mind me asking a few questions as my first post. I think I have an unusual issue and hope you guys can help.

I recently installed a cellular phone booster in my 04 Toyota Tacoma. Even thou it is a double cab, by todays standards it is a small truck.
The cell booster I have is the weBoost Drive Reach. What I have figured out it is basically a bidirectional cell signal repeater. There is a in-cab antenna that the cell phone connects to. The external outside antenna connects to cell towers and is boosted to 50 watts. The outside antenna is a dreaded mag mount. I have separated the two antennas as far as possible but they are still only 6 feet apart. Feed back and oscillations are the big issue. The Drive Reach will self test at start up and if feed back is excessive then the unit will shut down.

I want to change over to a MNO mount and antenna for the cell booster. I already have a MNO 2m/70cm mount so another hole is not a problem.
The question I have is weBoost tech support advised against a MNO mount for this system. They said that the MNO mount will have more internal cab RFI and increase the chance of oscillations.

Would you agree or disagree that a MNO mount is more RF leaky than a mag mount? Could effective shielding be fabricated?
The mount I plan to purchase ether is pre wired with RG/58 or Low Loss 195. Is there any advantage to ether one for RF leakage?

Thanks

 

[mikewazowski]

What I have figured out it is basically a bidirectional cell signal repeater. There is a in-cab antenna that the cell phone connects to. The external outside antenna connects to cell towers and is boosted to 50 watts. The outside antenna is a dreaded mag mount. I have separated the two antennas as far as possible but they are still only 6 feet apart. Feed back and oscillations are the big issue.

50dB of gain not 50W.

The issue probably isn’t RF leakage but the fact most NMO antennas would have more gain then the little antenna supplied with the unit. That means more signal getting back into the cab and potentially being picked up by the internal antenna.

 

[mmckenna]

Yeah, I'd probably agree on that.
For the record, the Wilson brand antennas and cable/mounts is about as crappy as you can go. I'd expect that from them, and it's sort of nice to see them acknowledging it (sort of).

If you went with an NMO mount better than Wilson, you'd probably be OK. Get away from their cheap cable and use something decent.

Dual shield RG-58 on a good NMO mount would be a good choice:

https://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=264_266_291&products_id=1125

Make sure you route the cable well, and keep it separated from the BDA and it's internal antenna as much as you can.

I used to have a Wilson booster in a 2005 Chevy Colorado extended cab, so same size truck. I had a permanent mount NMO on the back of the cab with a Larsen antenna. I had no issues with self oscillation and it worked quite well.

 

[btu44]

Yes I see I miss read the gain. Thanks for the correction

I had not thought about the higher gain of the outside antenna would hit the inside antenna more. Make sense to me. Maybe why I see installations on trucks use the RV antenna that does not need a ground plane. Then they can mount the antenna to the back of the truck for more antenna separation.
With my current setup the booster will start up with a solid green LED 75% of the time. A green LED means that feed back is in tolerance and no inside antenna attenuation was needed. About 23% of the time it starts up with a flashing red LED then goes solid green. I understand this to mean the inside antenna needed attenuation to get the feed back to a safe level. Very occasionally the unit will startup solid red meaning too much feed back and the unit shuts down. I figure overall my setup is okay but close to the edge.

The MNO mount I was going to get is this. I like this mount for it's shock absorbing. The truck is often off road in forested areas.

NMOHPCN518 TE Connectivity Laird | RF/IF and RFID | DigiKey

Order TE Connectivity Laird NMOHPCN518 (994-1123-ND) at DigiKey. Check stock and pricing, view product specifications, and order online.

www.digikey.com

I was considering this antenna. What do you think?

Amazon.com: LAIRD TECHNOLOGIES TRA6927M3NB-TS1 Phantom 698-2700 MHZ 3G/4G/LTE NMO- Ground Plane REQD, Antenna

Amazon.com: LAIRD TECHNOLOGIES TRA6927M3NB-TS1 Phantom 698-2700 MHZ 3G/4G/LTE NMO- Ground Plane REQD, Antenna

www.amazon.com

I used to have a Wilson booster in a 2005 Chevy Colorado extended cab, so same size truck. I had a permanent mount NMO on the back of the cab with a Larsen antenna. I had no issues with self oscillation and it worked quite well.

Do you have the part # for the Larsen antenna you used?

 

[WB9YBM]

I'm assuming there's a metal roof between the inside antenna & the outside antenna. If so, I'm wondering if this could be a grounding issue: if the metal of the roof is not grounded properly to the antenna ground, then the metal of the roof will not provide proper RF shielding.

 

[RFI-EMI-GUY]

I cannot see how an NMO mount or high gain antenna would increase the signal levels inside the cab.

1) an NMO mount, especially with double shielded cable will put the majority of the signal outside the cab.
2) A gain antenna on the cellular band (s) of interest will put more signal at the horizon and thus less will be coupled into the cab..
3) Ideally the antenna should be centered on the roof to prevent coupling back into a window.
4) Cable routing from the outside NMO antenna should be via a route as far from the amplifier and inside antenna as possible. Take a route down the rear passengers side pillar (opposite the drivers seat). Coil any excess near the rear cab wall or cut to length.
5) The inside antenna should be close to the phone operating location but as far from windows as possible. The front footwell would be best.
6) The inside cab antenna cable and the amplifier should each be RF bonded to the vehicle body.

 

[btu44]

I would like to thank everybody for helpful replies. I feel fairly comfortable "drilling the hole"
I have a Larsen MNO + HF mount and Larsen antenna on the way.
I'll let you know how things go.

 

[JoshuaHufford]

I have 2 cell boosters from a different brand (SureCall). Interestingly they sell a version that comes with a NMO mount, odd that weBoost would tell you not to do it. SureCall also has a tech support email address that you actually get a response in about a day, it is from someone that actually knows what they are talking about, and is quite friendly, for this reason alone it will probably be the only brand I buy if I need another or a replacement.

The Laird antenna you linked above is the same antenna that comes with the kit I bought, just rebranded with SureCall. I have not had the problems that you have had, only time I see any lights go red (meaning unit has shut down) on my unit is when I'm right next to a cell tower, and then I don't need it anyway, otherwise it works fantastic.

What kind of inside antenna does yours come with? Mine has a small flat antenna with about a 45 degree radiation pattern, in both of my vehicles they are mounted between the front two seats pointed down. In my Subaru I have it hidden above my headliner, in my Ford Transit Connect it is mounted on the console just below the roof.

If properly installed I just don't see how an NMO mount would increase problems, honestly sounds like they just don't know what they are talking about, or their products are poorly designed. But maybe they know something I don't.

 

[Ubbe]

Remember that boosters only work properly when there's no objects nearby, like a builiding or other objects that will reflect the booster transmit signal and bounce back into the windows of the vehicle. I guess the booster are to be used only out in the wildernes where there are far between the cell towers and no buildings by the roadside. But it seems that it automaticly turns itself off when conditions are not the right ones to not ruin the communication.

Just see to that the coax or the boxes do not leak RF. Double shielded coax seems like a good idea.

/Ubbe

 

[RFI-EMI-GUY]

I would like to thank everybody for helpful replies. I feel fairly comfortable "drilling the hole"
I have a Larsen MNO + HF mount and Larsen antenna on the way.
I'll let you know how things go.

Be sure to get the proper size hole saw. Some of the ones sold for electrician conduit work are "trade sizes" which are too large.

 

[btu44]

What kind of inside antenna does yours come with? Mine has a small flat antenna with about a 45 degree radiation pattern, in both of my vehicles they are mounted between the front two seats pointed down. In my Subaru I have it hidden above my headliner, in my Ford Transit Connect it is mounted on the console just below the roof.

The inside antenna is a rectangular shape maybe 3 x 1 x .25". I placed the inside antenna under a dashboard liner. The last step I did after amp mounting and outside cable routing was check different inside antenna locations in the cab. None seemed to make much difference during the start up feedback self test...although that maybe for not because of what Ubbe mentioned below.

Remember that boosters only work properly when there's no objects nearby, like a builiding or other objects that will reflect the booster transmit signal and bounce back into the windows of the vehicle. I guess the booster are to be used only out in the wildernes where there are far between the cell towers and no buildings by the roadside. But it seems that it automaticly turns itself off when conditions are not the right ones to not ruin the communication.

/Ubbe

Very good point and obvious now that you mention it. I've been doing most of my testing in my driveway. Brick wall on one side, house and garage on the others. For good measure a tall metal gate across the driveway. I will keep this mind after installing the new antenna.

Be sure to get the proper size hole saw. Some of the ones sold for electrician conduit work are "trade sizes" which are too large.

Fortunately I saved and more amazingly found my Laird MNO hole saw. No need to put a hole in the roof and the headliner

 

[03msc]

It will work fine. I run an NMO on the roof with mine. Zero issues, improved performance. Use their NMO antenna or another that covers the appropriate bands (frequencies). They sell NMO antennas for them so I'm not sure why support would have said that unless they somehow misunderstood what you were asking...or just didn't know.

The boosters are solid performers and do what they advertise. The mag antenna they ship with them is disappointing but it seems to be what's popular. Of course, the bigger OTR or overloading antenna now seems to get gaining popularity and definitely performs better.

I have their 12 inch NMO antenna (311104) and also their low-profile NMO (314405) and they both do well. I typically run the low profile except for when I'm going to an area I know is on the fringes.

 

[btu44]

This is good to hear. Sounds like from the replies so far everything will be fine. I have realistic expectations. I know it will not pull a signal from nothing but will improve my chances with a weak one.

My primary goals is to send and receive text updates while remote 4WD off roading. What usually happens is I'll write some texts that will not be sent because of a lack of signal. I'll drive around for awhile and next time I check the phone I will have sent and received texts. I guess I drove up a peak or through a valley were a cell tower had line of sight or close enough. I figure the amount of data in a text is so small that a send and receive is just a quick burst. I am hoping the cell phone booster will at least improve the chances of getting texts.

About Tech Support maybe giving not so good advice. They still have my sympathies. Can you imagine the daily dose of grief the support agents gets from people upset that there $500 cell booster doesn't get a signal from nothing.

Going on a 3 day Mojave desert trip starting tomorrow. This should give me a good base line for the performance of the mag mounted antenna.

 

[JoshuaHufford]

Let us know how it works for you.

 

[jeepsandradios]

I run a wilson BDA in my work truck. I have a larsen NMO mount and Laird pepper shacker antenna. Never had an issue with the amp looping up.

 

[mmckenna]

My primary goals is to send and receive text updates while remote 4WD off roading.

You should really, seriously, look into a device like a Garmin InReach. They allow sending text messages via satellite and will even tag messages with your location. Added benefit is an SOS button that will get you help if you need it.

I spend a fair amount of time in remote areas, both for work and recreation. I've got several radios in my work truck, plus portables and even a satellite phone. I still carry a Garmin InReach Mini with me.
When I'm off having fun, I take the same Garmin device with me. Really easy to send a message to my wife so she knows I'm still alive.
It is a subscription based service, but $13/month is not a lot of money, and those devices can really pay for themselves.

 

[btu44]

I totally agree the Garmin InReach Mini is the ultimate way to go for true remote excursions. A guy at work used one hiking the John Muir trail and liked it a lot. It just a little bit more I want to spend for a need a few times a year. Also I do most of my off roading the SoCal area, there is really not many "remote areas" accessible to vehicles.

The first test run of the cell booster went really well. I was quite impressed. The following screens were made 5 miles past were the cell phone had an un-boosted signal. The location was in a dry lake bed surrounded hills.

Google Earth

earth.google.com

Without booster


With booster


Was able to call home anytime. The next day I explored some new trails for 85 miles. I had cell coverage 90% of the time.
This thing is great with the mag mount antenna except for the freeway 'whistle' noise. This it's from the coax going through the door weather stripping. I'll have the NMO antenna installed this weekend so that will fix that.

Thanks to all for all the help. I'll let you know how the NMO antenna goes.

 

[mmckenna]

I totally agree the Garmin InReach Mini is the ultimate way to go for true remote excursions. A guy at work used one hiking the John Muir trail and liked it a lot. It just a little bit more I want to spend for a need a few times a year. Also I do most of my off roading the SoCal area, there is really not many "remote areas" accessible to vehicles.

OK, yeah, SoCal you probably don't need one. Up in Northern California, it's easy to get into cellular dead zones for long periods of time. The Garmin's are nice to have, but the upfront cost and $13/month for occasional use isn't the best solution for everyone.

Was able to call home anytime. The next day I explored some new trails for 85 miles. I had cell coverage 90% of the time.
This thing is great with the mag mount antenna except for the freeway 'whistle' noise. This it's from the coax going through the door weather stripping. I'll have the NMO antenna installed this weekend so that will fix that.

Thanks to all for all the help. I'll let you know how the NMO antenna goes.

Yep, one of the issues with mag mounts. The NMO mount will solve that, although it's not uncommon to get some whistle from the antenna in some situations. Mine will do it when it's foggy.

The NMO mount will also look a lot better, and you may even see some better performance.

 

[btu44]

The Larsen antenna arrived yesterday and install will be this weekend. The one I bought is this:

PulseLarsen Antennas | SLPT698/2170NMOHF

www.pulselarsenantennas.com

It is a very nicely made antenna. Heavy metal base with a well molded plastic upper radiator.
I see the rated freq range is 698-960 / 1700-2700Mhz.

My cell carrier is AT&T. Their freqs:
4G LTE

• 700 MHz: Bands 12/17/29.
• 850 MHz: Band 5.
• 1900 MHz: Band 2.
• 1700 MHz /2100 MHz: Bands 4/66.
• 2300 MHz: Band 30.

3G GSM/UMTS/HSPA+
1900 MHz, 850 MHz

Even thou this is not a "Approved antenna" as far as the FCC is concerned. I believe it will work well and not cause problems on the network.
Do you guys agree?

 

[mmckenna]

The Larsen antenna arrived yesterday and install will be this weekend. The one I bought is this:

PulseLarsen Antennas | SLPT698/2170NMOHF

www.pulselarsenantennas.com

It is a very nicely made antenna. Heavy metal base with a well molded plastic upper radiator.

They are solid antennas. I think that is the same one I used back in 2007 or so.

Even thou this is not a "Approved antenna" as far as the FCC is concerned. I believe it will work well and not cause problems on the network.
Do you guys agree?

The FCC doesn't approve antennas. The capability of the antenna will match up well with AT&T service, and just about all other cell carriers. It won't cause any problems on the network.