VHF mobile to mobile question

[HartB]

Just joined the forum and haven’t seen a vhf mobile category yet so I’m thinking this may be the appropriate place. Our farm has recently gone to vhf radios. From my understanding several farmers have purchased channels in the business band or MURS area of the spectrum. Unfortunately the local “professional” is so overwhelmed with government and public service accounts that he couldn’t take on 30+ tractors and trucks to do. So I have been given the opportunity to clean up what has been done by the individual farmers to improve their systems so to speak. There are no repeaters or stationary antennas just mobile units in simplex operations. I’m no engineer by any means but I have mentored with a very experienced individual who was employed by the government in the communications industry and operated his own two way and cellular business for 40+ years. I have a very strong knowledge of mobile systems and how to install them in a semi professional manner with the tools I have. He has since passed away so I’m coming here for some pointers as I see there are some very knowledgeable folks here. My question is rather simple yet redundant now that you have read the backstory. What mobile antenna should I use in this situation where we are not on a repeater and our locations can be as far as 15 miles apart in some places and the elevation is somewhat flat yet can vary drastically between 2 locations? Currently everything used is whatever cost the least and was immediately available. My goal is to standardize everything with NMO mounts and commercial antennas of either Larsen or PcTel flavor. I understand theoretically a 5/8 antenna will give us the range we are looking for. Our obstacles are tractors not being a very good antenna platform and the bandwidth is somewhat narrow. Several farms would like to communicate with each other for various operations. Given the electrical and physical parameters would a 5/8 or possibly a wideband 1/2 wave be the better choice? The 1/2 wave I THINK would give better performance on the compromised platforms and offer a wide enough bandwidth to prevent the radios from folding power back due to swr issues. Some of the channels are 4-6 MHz apart and that seems like a good stretch for a 5/8 without a “perfect” ground. A central repeater would help but from what I’m being told is not financially feasible at this time. I apologize for the very long post but I’m trying to offer as much info as I can so the great minds can have what they need to go by. I’d like to get as much range from mobile to mobile as possible. Area of operation is south east Georgia roughly 50 miles from coast.

 

[mmckenna]

You mentioned MURS, but you also mentioned business band. If some users are operating under FCC issued licenses for non-MURS frequencies, you would need to look at those licenses and see what power output is permitted by the license, and if there is an ERP (Effective Radiated Power) limitation listed. If there is an ERP, you need to figure out what the transmitter power output is and add in the antenna gain to confirm ERP will be at or below what the license allows.

If MURS is being used, make an attempt to be sure radios are legal for MURS. Mobile mount radios for MURS that meet all the requirements are very difficult to find. MURS rules are very specific and have some limitations.

Unless you have control over every install, you are right to consider the antenna choice as part of this. It's rare to find non-radio types that will put more than a few seconds of thought into proper antenna location. Usually it's "slap it where ever is easy" and go on with their day.
Based on that, I'd agree that the 1/2 wave would be an easier choice.

The half wave will work without a ground plane, and it'll work better with one. Keep in mind that if someone is mounting them off to the side of the ground plane with a bracket it is going to result in a lopsided ground plane, that that will impact range. I'd recommend putting a LOT of effort into the antenna installation if you want reliable range, or at least making sure others understand that range will directly be impacted by antenna installation.

5/8th's would give you more gain, and should have plenty of bandwidth for 4-6MHz of spread. They do need a suitable ground plane if you want them to work well. That means about 18" in all directions around the antenna of an electrically conductive surface. This will work much better than a poorly mounted 1/2 wave antenna.

Larsen is an excellent choice. I've been using their antennas for 30+ years without issue. EM Wave is another good manufacturer. I've started using/spec'ing all EM Wave antennas at work. If others are going to be buying their own antennas, you'll have even more work cut out for you. Again, people will take the cheap and easy way out in most cases. The antenna is the most important part of the radio system, and cutting corners there will directly impact performance.

So, yeah, performance is going to really depend on antenna choice and proper antenna installation location.

15 miles range may be possible with a properly coordinated and licensed frequency that can run some power, but unlikely you'll see 15 miles of range reliably with the 2 watts permitted on MURS.

 

[HartB]

Thanks for the info. They are on business channels that are near the MURS frequencies and I will look at the power threshold to confirm but I was told by the person who originally set up getting the channels that they could use 50 watts. This may or may not be accurate so I will confirm. They did purchase the radios from the local shop that does all the county and emergency management work with their specific frequencies he just couldn’t take on another account that large so the antennas and installs were left to the customer. This is what they have asked me to look at after they have realized their approach wasn’t the best. The antenna is the most important part of the system and getting the power from the radio to the antenna should also be high priority. Most have 1/4 wave just slapped wherever they could get to and I have learned that the 1/4 waves are very sensitive to ground surface. I’ll use 5/8 where I can get adequate mounting arrangements and use 1/2 on the more stubborn locations and tune them all in with the antenna analyzer I have. I also have used Larsen products extensively for the last 15-20 years and know they make some of if not the best mobile antennas out there. I’ve seen Pctel coils fall apart and some have filled with moisture in high shock environments and the finish of the chrome parts is prone to corrosion especially around the whip and set screw points. This might be from the southern environment having enough salt in the air to do this or it could be the antenna. I feel pctel is a good antenna electrically but the fit and finish is not on the level of Larsen. The new em wave stuff looks promising as well. Thanks for your response.

 

[mmckenna]

I've been using EM Wave for a few years now and have not been disappointed. On par with Larsen for quality. Their base sealing design is pretty nice. I've recently been spec'ing them for use on a bus fleet where the antenna gets mounted on the roof and not touched for the life of the bus. Pretty happy with them.

50 watts, a good antenna and proper mounting should give you all you can get out of the setup. Without a repeater, range may not quite make 15 miles in every situation.

Other variable to look at is the actual radio installation. Make sure 12vdc comes right off the battery. Tapping existing wiring can result in noise that can limit range.

 

[HartB]

Yes I’m sure I’ll end up with a few that aren’t battery powered directly and will correct that as well. I’ve always hounded others I know that play with radios about power direct to battery. To me little things like that are standard practice but not everyone else cares. If it lights up and makes noise they think it’s done.

 

[AK9R]

Yes I’m sure I’ll end up with a few that aren’t battery powered directly and will correct that as well.

I'm not crazy about going directly to the battery. In modern automobiles, and, I assume, modern farm equipment, the current going into and out of the battery is carefully monitored to make sure the battery isn't over drawn. For example, Ford trucks since about 2011 have had a battery control module that monitors the current going back to the battery and controls supply current to accessory circuits. The BCM will shut down low-priority accessory circuits if the return current is too high.

If you can get the wiring diagram for the equipment you are working on, that would be great. If not, follow the high current positive wire from the battery. It will probably go directly to the starter and distribute to lower-current circuits from there. Or, there may be a lower-current wire from the battery going to a distribution block. I think I'd land your positive wire for the radio there...with appropriate fusing. I'd land the negative radio wire directly to the frame or chassis of the equipment. @mmckenna may have some additional thoughts about this.

 

[mmckenna]

Never worked with tractors, but I'd agree, negative power wire from the battery always to a body or chassis ground, not directly to the negative terminal.

I'm sure John Deere, Caterpillar and others have some guidance on 2 way radio installation.


I have done a few UTV's where ground plane is a challenge and noisy electrical systems are common. It can be a challenge getting everything to play nicely.

 

[HartB]

I know the new fords monitor the ground side of the battery. There was a tech bulletin put out about it with instructions for properly wiring accessories to the battery. You can connect positive direct but there is a sensor on the ground side that you must connect on the proper side of. Done several newer fords with no problems one being my fathers new ‘24 about 2 months ago. Most of what I’m dealing with in this situation is older equipment and the newer stuff I can call my buddy who is a tech for the John Deere dealer that it would come from for proper procedure if need be.

 

[HartB]

Never worked with tractors, but I'd agree, negative power wire from the battery always to a body or chassis ground, not directly to the negative terminal.

I'm sure John Deere, Caterpillar and others have some guidance on 2 way radio installation.


I have done a few UTV's where ground plane is a challenge and noisy electrical systems are common. It can be a challenge getting everything to play nicely.

Any UTV I do gets 1/2 wave antennas. I’ve pulled my hair out trying to get 1/4 and 5/8 to behave but without adequate counterpoise. I just did one a few days ago where I used 5/8 and somehow got acceptable results. This was all I had left to sell and I wasn’t really happy with it but the customer was happy I got anything to work better than his handheld that he was tired of charging and lugging batteries for. I’m just a normal guy doing this out of my truck basically but in the last 6 months I’ve been hammered with requests after a few people found out I know a little bit about radio. The only other place the general public has to go in this area is 60 miles away and I’ve been told they are now charging $200 for installs. I charge less than half that but I don’t have storefront inventory or employees. I think it’s time to bump the price up enough so I can afford to keep some sort of inventory at least. Not really looking to run this as a full time thing I like helping people when I can but if things keep going at a steady pace I’ll be faced with that choice. Right now I enjoy radio I know if I dive in full time that will change. For now I’m going one step at a time.

 

[mmckenna]

I'm about 5 years out from retirement and have given serious thoughts to doing some level of mobile install work out of a truck. Not heavy public safety type stuff, but ag/construction type work. There's still a few shops around me, but most of them do pretty awful work.
From hanging out on this site for a few years, there's a market for permanent NMO installations for the hobby users.

 

[AK9R]

From hanging out on this site for a few years, there's a market for permanent NMO installations for the hobby users.

How good of a salesman are you? The first hurdle in your business plan is convincing hobbyists that a NMO mount is better and won't degrade the value of their rusty 15-year-old pick-up truck.

 

[mmckenna]

How good of a salesman are you? The first hurdle in your business plan is convincing hobbyists that a NMO mount is better and won't degrade the value of their rusty 15-year-old pick-up truck.

Glad you mentioned that, I specialize in rusty 15-year-old pick-up trucks! And the wife's minivan.

 

[ladn]

From hanging out on this site for a few years, there's a market for permanent NMO installations for the hobby users.

Have hole saw-will travel.

 

[10-43]

One thought on tractor antenna installations. I have noticed the roof of many cabs are plastic or maybe fiberglass. You will need a metal ground plane. NMO is the best choice, but getting the antenna on top of the cab is the place to be. Height is a big advantage. You can fabricate or buy circular ground planes to mount on the bottom inside of the NMO hole mount.

A 5/8 wave antenna will get you about double the effective radiated power, Not double the distance, and can compensate for the feed line loss. Remember the power is spread out over the area around the antenna. It does this by flattening the RF field to a more donut shape than a ball shape so more power goes outwards than up and down. It also improves receive.

I wonder if the state department of agriculture or farming co-ops may have resources in the form of frequency usage/licensing and radio equipment vendors/discounts or power purchasing.

 

[kayn1n32008]

Yes I’m sure I’ll end up with a few that aren’t battery powered directly and will correct that as well. I’ve always hounded others I know that play with radios about power direct to battery. To me little things like that are standard practice but not everyone else cares. If it lights up and makes noise they think it’s done.

Keep a watch for 24v systems. LMR radios reaaaaalllllllllyyyyyyyyy do not like 24v.

 

[kayn1n32008]

One thought on tractor antenna installations. I have noticed the roof of many cabs are plastic or maybe fiberglass. You will need a metal ground plane. NMO is the best choice, but getting the antenna on top of the cab is the place to be. Height is a big advantage. You can fabricate or buy circular ground planes to mount on the bottom inside of the NMO hole mount.

A 5/8 wave antenna will get you about double the effective radiated power, Not double the distance, and can compensate for the feed line loss. Remember the power is spread out over the area around the antenna. It does this by flattening the RF field to a more donut shape than a ball shape so more power goes outwards than up and down. It also improves receive.

I wonder if the state department of agriculture or farming co-ops may have resources in the form of frequency usage/licensing and radio equipment vendors/discounts or power purchasing.

If there isn't a proper groundplane to work with, 1/2 wave is the way to go. If the spread between the lowest and highest is more than about 4MHz, a 1/2 wave is the way to go.

I'm guessing the OP won't be dealing g with much distance, especially if it's all simplex.

If there is metal bars of any kind for mirrors, I'd just use a NMO mirror mount bracket. They are incredibly common where I live for oilfield transport trucks and logging, where VHF simplex is king, and CB is non-existant. Don't over think this, ad don't worry about adding groundplanes to Fibre glass roofs.

This isnt some hammy set up, where they are looking to get every centimeter of distance out of their mobile install. It is likely going to be, relatively, short range comms over less than a dozen miles.

I reliably got between 10 and 20km(6 to 12m) in the mountains of western Alberta and Eastern BC, spanning roughly 24MHz of VHF spectrum(oil patch frequency assignments here span 150-174MHz) using a 1/2 wave on a fender mount L-Bracket when I was working in the oilfield.

KISS: L-Brackets and mirror mounts with 1/2 wave antennas. No need to go all out with drilling roofs and buying groundplanes.

 

[kayn1n32008]

Just joined the forum and haven’t seen a vhf mobile category yet so I’m thinking this may be the appropriate place. Our farm has recently gone to vhf radios. From my understanding several farmers have purchased channels in the business band or MURS area of the spectrum. Unfortunately the local “professional” is so overwhelmed with government and public service accounts that he couldn’t take on 30+ tractors and trucks to do. So I have been given the opportunity to clean up what has been done by the individual farmers to improve their systems so to speak. There are no repeaters or stationary antennas just mobile units in simplex operations. I’m no engineer by any means but I have mentored with a very experienced individual who was employed by the government in the communications industry and operated his own two way and cellular business for 40+ years. I have a very strong knowledge of mobile systems and how to install them in a semi professional manner with the tools I have. He has since passed away so I’m coming here for some pointers as I see there are some very knowledgeable folks here. My question is rather simple yet redundant now that you have read the backstory. What mobile antenna should I use in this situation where we are not on a repeater and our locations can be as far as 15 miles apart in some places and the elevation is somewhat flat yet can vary drastically between 2 locations? Currently everything used is whatever cost the least and was immediately available. My goal is to standardize everything with NMO mounts and commercial antennas of either Larsen or PcTel flavor. I understand theoretically a 5/8 antenna will give us the range we are looking for. Our obstacles are tractors not being a very good antenna platform and the bandwidth is somewhat narrow. Several farms would like to communicate with each other for various operations. Given the electrical and physical parameters would a 5/8 or possibly a wideband 1/2 wave be the better choice? The 1/2 wave I THINK would give better performance on the compromised platforms and offer a wide enough bandwidth to prevent the radios from folding power back due to swr issues. Some of the channels are 4-6 MHz apart and that seems like a good stretch for a 5/8 without a “perfect” ground. A central repeater would help but from what I’m being told is not financially feasible at this time. I apologize for the very long post but I’m trying to offer as much info as I can so the great minds can have what they need to go by. I’d like to get as much range from mobile to mobile as possible. Area of operation is south east Georgia roughly 50 miles from coast.

KISS and don't over think this. It's short range simplex spanning 4-6MHz:

-1/2 wave antennas using using L-Brackets and mirror mounts.

-Watch out for 24v power systems. You will need a DC-DC converter, LMR radios really do NOT like 24v. If it's 12v, watch out for a main battery disconnect. Don't go directly to the battery if it has one.

Short range, mobile to mobile, VHF comms are a staple in western Canada in the logging/OTR trucking/oilpatch. This is going back to crystal and burned prom based mobiles.

Logging, OTR trucking, and oilpatch trucking(class 1/A CDL) are either using mirror mounts or L-Brackets. Its quite rare to see a drilled NMO mount in a roof. For 1/2->1 ton pickups in the logging and oil field,, it's either fender mounted L-Brackets or mag mounts.

 

[Project25_MASTR]

I'll add to this…

Several tractor manufacturers (John Deere being one) have a factory option for a "business band radio kit" and come with an installed NMO mount in the roof that is "supposed" to have a some light copper braid running from it to the A pillar of the ROPS. In the case of JD specifically, the cubby for the factory AM/FM radio with have a power lead (switched on accessory) and the coax which has had a UHF connector installed every time I've found a virgin BBR option. The power lead is .16 ga if I remember correctly but should be fused for 15A.

While I believe a half-wave solution is the best option for most tractors (JD stopped using metal roofs in the late 80's) when you start talking your larger machines like the 8000 and 8R series…the top of the cab is already pushing 10 feet so tickling utility lines becomes a concern. Not to mention you have combine hoppers and stripper baskets that can be taller than the cabs.