Batboard

I need some advice on selection and placement of a large complement of antennas on top of a crew cab pickup. The vehicle will have 1 APX6500 VHF high power, 1 APX7500 VHF/UHF high power, 1 APX7500 VHF/700/800 high power, plus a Havis docking station for a Panasonic CF-31 with LTE and GPS antennas. So that's 3 x VHF, 1 x UHF, 2 x 700/800 (1 radio and 1 LTE card) and 1 GPS. Other than the standard "as far apart as possible" what can anyone offer? Is better in the middle vs the side, etc? 1/4 wave vs other antenna types? I plan to add additional shielding in the bundle going down in the form of tinned copper braided sleeving and bonding it to the vehicle body. Is that a good idea or will it create its own problems?

cogburne wrote:I need some advice on selection and placement of a large complement of antennas on top of a crew cab pickup. The vehicle will have 1 APX6500 VHF high power, 1 APX7500 VHF/UHF high power, 1 APX7500 VHF/700/800 high power, plus a Havis docking station for a Panasonic CF-31 with LTE and GPS antennas. So that's 3 x VHF, 1 x UHF, 2 x 700/800 (1 radio and 1 LTE card) and 1 GPS. Other than the standard "as far apart as possible" what can anyone offer? Is better in the middle vs the side, etc? 1/4 wave vs other antenna types? I plan to add additional shielding in the bundle going down in the form of tinned copper braided sleeving and bonding it to the vehicle body. Is that a good idea or will it create its own problems?

My bet is you start cleaning out the front end of the receivers with all the high power radios. Kind of a poor choice of radios with the limited roof area.

Jim

Time for a dbSpectra combiner.

Bill_G wrote:Time for a dbSpectra combiner.

Still will not prevent burning out a receiver.

You do NOT have enough real estate to get any sort of antenna separation. These newer radios can not take that kind of RF down the receiver without component failure. They are flat out NOT made for that kind of abuse.

I would tend to disagree.

On the topper of my truck (roughly 6.5' long), I have a 3x5 grid of antennas. VHF, UHF, 700/800. Connected to those antennas are XTL, APX, TK-x180, VRS750, and an 8-port receiver multicoupler. There is another truck configured very similarly, and I had similar configurations/spacing in at least 6 other vehicles in the past 10 years. So far, the only front end I've ever taken out is an Optoelectronics Scout frequency counter.

I do run all mid-power (50 watt) radios, but I haven't always done that. In fact, in one of the builds, the highest duty cycle radio was a 110-watt UHF X9000. However, if you don't really *need* high-power, I would suggest programming the radios down to 50 watts. 3dB is really insignificant in the grand scheme of things.

I pull all of the drawers at least every couple of years and every time they move to a new vehicle and check the alignment and sensitivity on a calibrated service monitor. Haven't had one fail yet due to abuse (I've had a couple of Spectras/Astro Spectras go wonky over the years - usually thanks to time-bomb capacitors). Indeed, my only current issue is the LO of an XTL getting into one of the Kenwoods in dense urban RF environments (haven't resolved this issue yet).

To the OP, I would first suggest trying to combine what you can. For instance, look at the Mobile Mark LTM501 antenna. This gives you GPS, WiFi, and PCS/LTE on one antenna with 5 coax feeds. In this model, both WiFi and LTE have 2-slot MIMO antennas. This makes a great pair to the Cradlepoint IBR600, if you have the coinage available.

I wouldn't worry about your braiding idea. I have had good luck with Larsen's mounts, part NMOKDS. This is RG-58 stranded, but dual shield. It makes a world of difference. I would not go with solid-center coax in vehicle applications... I've done it, it's a pain.

The downside to the roof of a pickup is height - especially if you're talking a 4WD and/or 3/4-ton-plus configurations. Are you planning to park in parking garages or drive through any sort of low-hanging brush? Or will the vehicle be used for emergency purposes, where you may not be thinking about such things? If so, I would steer away from long antennas and stick with quarter-waves, possibly spring-loaded. You might also consider using the NMO mounts that only require a 3/8" hole. These must be mounted from the bottom (so you will need to be able to reach them), but you compromise the integrity of the roof less thanks to the smaller hole.

Is this a new/newer truck? If so, you will have side airbags to deal with (even at the 450/550 class these days). That's not a big deal, but you do need to be cautious and think about the airbag deployment path. You would also be wise to pull ground off the battery and give the system 30 minutes to discharge before doing any drilling/running of coax. Better safe than sorry.

Now, with all that said... assuming you wouldn't tear these off the roof, have you considered:
https://www.tessco.com/products/display ... ventPage=1 and http://www.panorama-antennas.com/datash ... BA-BNC.pdf

This would let you put a VHF, UHF, and 700/800 radio all on the same antenna. It would also keep out-of-band signals from interfering with the other radios. You still have in-band issues, of course.

What about three of the Laird antennas arranged in a triangle with the LTE/GPS/etc. puck in the center?

I would be concerned about cost - but, if you can afford three APX mobiles and a CF-31, you can afford some antennas and triplexers!

The vehicle is a F350 SRW 4WD, so height is an issue. A tree limb sliding along and tearing something off is a real possibility. That would be my primary concern with https://www.tessco.com/products/display ... ventPage=1.

If I were to use the Mobile Mark to combine GPS and 4G (Verizon so 700mhz) that would eliminate 1. What would be the advantage/disadvantage of running a combined VHF/UHF and combined VHF/800 over separate ¼ waves for the multiband radios that can’t transmit or receive through both antennas at the same time? Would the RF from, and excuse my ignorance here, the VHF transmitter of one radio cause issues the UHF and 700/800 receivers of another?

I was thinking VHF ¼ wave centered at the forward most position possible for the APX6500, which will see the most use, a ¼ wave VHF in the rearmost position possible and as close as possible to the driver side, the 3rd ¼ wave VHF in the rearmost position possible and as close as possible to the passenger side, the ¼ wave UHF and 3db gain coiled 14” whip 800 in the middle (front to back) and as close as possible to the driver and passenger side, respectively. The GPS/4G could then go in the center of the roof, front to back and right to left.

Also a little separate issue that will surely open up a can of worms. Every radio I’ve ever installed (30-40, not a professional installer by any means) I’ve run the ground back to the battery, either directly or through some kind a distribution stud, never to the body or chassis. Never had an real issues with noise on either end. I actually read the install manual and it specifically recommends against that. I don’t understand why it would be better to pull that 20 amps through existing ground straps that through a dedicated wire.

Thanks for all the help!

The Laird antenna is 20" tall. In comparison, a VHF quarterwave is 19". So, not a significant difference there. It also puts a 2.5" base on the roof - combine that with a 3/8" NMO mount and I would think the antenna would actually be stronger than a typical VHF quarterwave on a regular NMO. You can also pretty much forget any parking garage if you intend to install anything bigger than a low-profile antenna on the roof of that truck. If you're driving an F350 4WD, parking garages probably weren't a big worry for you anyway.

The big issue you'll have is in-band interference. The VHF 6500's transmitter wiping out the VHF 7500's receiver front end - temporarily or (the more concerning) permanently.

How about this:
Laird tri-bander front center (less likely to snag something if it's along the centerline) - 7500 VHF, 7500 UHF, 7500 800
VHF quarterwave - left rear - APX6500 VHF
VHF quarterwave - right rear - APX7500 VHF
Mobile Mark LTE/GPS - center - laptop

3 (obvious) antennas on the roof of that truck wouldn't look too whacktastic, and this configuration would give you reasonable spacing (at least a half wave).

In the event that you did need to go into a height-restricted area, you could swap the Laird to a UHF or 800 low-pro, and the two VHFs to VHF low-pros. The coverage would suffer severely and you'd lose one band on the tribander (RX might work OK, but TX would be bad), but at least you would have the option.

My concern with the Laird is the base not being forgiving, as opposed to the ¼ wave VHF. But if it was front mounted it would be less of a concern from tree limbs. Parking garages are of zero concern in this application.

If I went with the tri band that would have 2 separate radios, VHF/UHF from one and the 800 from another dual band radio going to the same antenna. What would happen if they were transmitting at the same time on the bands that share the antenna? Would the triplexer essentially disable one of the inputs while the other is transmitting?

I have a setup now with a XTL2500 and a CDM1250 both VHF midpower using ¼ waves a couple of feet apart and it does wipe out the receiver temporarily on the other while one is transmitting, so I expect that. I would like to avoid and permanent damage however.
Thanks again for all the help.