Vanagons, Antennas, Ham, CB, GMRS

I blame The Dukes of Hazzard.  


I've always had a thing for two way radios, and when I moved to the states in 1998, the first thing I did to the first vehicle I bought was to add a CB radio.  It didn't take long to discover with disappointment that no matter where I went, all I seemed to hear was an Elvis impersonator with tourette syndrome screaming at their echo mic.


Heading into the idea of a grim 2020 winter I was scratching around for ideas for a new hobby, and decided to study for the ham radio technicians license. Around the same time,  I looked at the various walkie talkies I'd picked up along the way and decided to go legit and buy the GMRS license.  That's when things got interesting.


What I didn't know is that beyond Walmart bubble-pack hand helds, there's a ham-ish GMRS community, and significant repeater infrastructure.   A repeater is a strategically placed device that "repeats" what it hears. It's a little bit more complex than that, but it's something that basically becomes the communications hub.  GMRS is up in UHF range which means it doesn't bounce around off the ionosphere like lower frequency ham bands.  It is "line of sight".  Going from one GMRS unit to another a couple of miles away n a city can be tough because of all the stuff in the way.  Going MANY miles to a repeater that is up in the air is easy though, so a well placed repeater can service an entire city - and in fact, a single repeater services the whole of Denver and surrounding areas.  It's not even very powerful.. it's just high up.


The realization that I could have meaningful communication with others from the Vanagon, and additionally have possible emergency service from the Vanagon or the motorcycles also appealed.




For ham you pass a test to show you have some level of understanding of the art, and at that point the FCC doesn't care if you transmit on a modified toaster.  Conversely for GMRS there is no test. Just a fee of $75 for 10 years that covers and entire family.  To keep things from falling into chaos,  the FCC mandates that only GMRS (Type 95) certified equipment can be used on GMRS. 


This is annoying.  It means that you can't legally use cheap ham radios on GMRS, and specific GMRS products are too locked down to be used on similar ham frequencies!


In reality I find the attitude towards bending GMRS rules to be quite common.  The attitude towards cheap handhelds like the ubiquitous Baofeng UV-5R is you shouldn't use them because they are crap, not because they aren't type certified.  At the end of the day, the GMRS community and repeater owners are much more interested in appropriate licensing and on air etiquette than hardware.


Still.  Regardless of what toys I may or may not collect along the way, I definitely wanted my primary equipment to be type certified and legit.  My selection was significantly influenced by owning before mentioned Baofeng UV-5R and a very similar Chinese radio typed for GMRS.  The GMRS radio was effectively the same thing with nasty hobbled firmware, locked down functionality and a non-removable antenna.  Kinda aweful. This made me look at the consumer GMRS mobile units, like the Midland offerings,  with some distrust.


With some research I discovered that people who are actually in to radios are more likely to be using cheap used business radios for GMRS than the $300 new consumer offerings.  Tried and tested radios by Kenwood, Motorola and Icom that are used commercially by the thousands across the world are readily available and can be reprogrammed with relative ease.


Each unit has it's own quirks and limitations and I went for the Kenwood TK-880.  I now have a TK-880 (25W) in the Vanagon,  and a TK-880H (40W) at home.  They cost around $100 each, and I spent $20 on a programming cable.   My decision was made in part because when I came across the local repeater groups info online, they stated several of the consumer products, like the Midlands can't be configured for the repeaters.  

The Version 2 units I have require a resister to be removed from the circuit board to allow adding channels from the front keypad, but at this point I'm happy enough with the channels I've added via the available PC software.


At the end of the day, if your area is serviced by a repeater that's pretty much what you'll be tuned to all day.  You'll need some info to successfully connect, and often that is something you have to request to avoid non-licensed from abusing them.  MyGMRS.com is a good starting point to finding out what is near you.


As a bonus, these Kenwoods work down to 440Mhz, so when I get my ham license I can hit the local ham repeater too!  As far as I can tell, using a radio like this is the only FCC legit way to use the same unit for GMRS and ham.



Antennas and Vanagons

I've learned a lot about antennas since starting this hobby and enjoy experimenting with making them.  In the photo above in my house you can see a directional "Yagi" style antenna I made for a few dollars that is my main antenna in the house for GMRS for now.  It's designed and built to be specifically tuned to the GMRS frequencies and  it works great.  


Vehicle antennas are a little more complex.  Most vehicle antennas are built to be mounted in the center of the roof or trunk and that metal "ground plane" is an essential element to transmission efficiency.   For Vanagons with a pop-top, this is a no-go so we have to resort to a different antenna specifically designed for "no ground plane / NGP" often used on fiberglass RVs or roof rack, bracket mounts.  


I antenna shopped with very little experience or knowledge, and it thankfully it turned out ok.  My criteria were:

  • support for GMRS frequencies of 462-470Mhz.
  • support for 70cm / 2m ham bands for the future
  • No Ground Plane
  • A spring for protection
  • Not crazy long!  

What I ended with, purely based on spec and reviews is the Browning BR-136


In general, the principles around antenna location are:

  • mount as high as possible
  • mount with as much space around them as possible

Theory is one thing, but luckily you can get really good results by trial and error with the right test equipment.  At the very least you need an SWR meter that will give you an idea of efficiency at a specific frequency, but there's a little tool called the NanoVNA for around $50 that gives you a visualization of the efficiency of the antenna over a range of frequencies which is awesome. 


With trial-and-error as a strategy, I purchased the most flexible mount I could find, and an antenna base.  The mount turned out to be the wrong sized hole, but I made it work.


Armed with the NanoVNA analyzer attached to the antenna in the mount I clamped it to various places on the van and found many places that it was terrible.


My original plan was mounting on the gutter rail right at the back and feeding the coax through the Vanagon air vent.  This location showed terrible SWR.  By moving around to various other locations near the back, my gut is this is due to interference from the roof rack.


The BEST SWR I could find was up front above the passenger door.  SWR was still at 3:1 which isn't good.   I experimented with physcially grounding the antenna and found zero impact.  In the end I took a piece of scrap steel and added it between the antenna and the mount and saw huge improvement!  I then just clamped it in various places until I found something optimal, which turned out to be on a short piece of aluminum bar stock attached to my awning mount bracket.  Don't ask me WHY this works really well.. it just does.  It's also a good spot for the wiring as that can be teased under screw on lip that attaches the pop top fabric.

This was first day out, and it needs some paint but performed really well.  To put GMRS in perspective, on this day our local GMRS group drove in various directions to test the repeaters.  I was 49 MILES from the repeater here,  5 miles down a dirt road with no cell coverage. I could hit the repeater clear as day with the Kenwood, and even with a 5W handheld. The safety implication for  trail bike riding here in the future is significant.



But really.. why?

Why is a great question.  


It's fun, it's a safety backup and it's keeping my mind off the fact that there's a global pandemic.


Write a comment

Comments: 0