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Expectations for GMRS

Acorn12

Member
Joined
Feb 18, 2024
Messages
8
Hi guys, I'm new to radio. Planning for general family preparedness. I have my GMRS license/working towards ham as well. I bought the Wouxun Kg1000g, BTECH UV-50X2 and a few UV5Rs. I live on Long Island NY/Queens. I like the idea of portability/mobility so I bought two N9TAX slim jim antennas in murs/gmrs as well as one in 2m/70cm for the UV5R. All I'm looking to do is talk back and forth with family if cell service goes out. My parents are getting old so I am keeping them in mind and will be giving them one of the 50 watt radios mentioned as well as the slim jim (until I know more about antennas). I got the slim jim since it can be easily rolled up and stowed away and traveled with plus it can be hoisted high up in a tree or put on a long pole and hoisted up/taken down.

*How far should I expect to reach via simplex with the slim jim antenna 25 ft up on Long Island? There is a repeater 16 miles away from my parents run by BTG communications (they have 3 repeaters connected) and pretty much covers the whole of Long Island so I am excited to join and pay the yearly fee to use their repeaters. I am 20 miles from parents when in Queens and 52-55 miles from them when out on Long Island. I bought lmr240 cable in 33 ft lengths for the slim jim antennas.

Any antenna recommendations for home base you guys can recommend for permanent roof mounting? I see Ed Fong makes a few.

How much further will I reach with a roof antenna compared to a simple car roof antenna on an aluminum cookie plate put up on the roof? Would a boat antenna work? (it can be folded down and back up when not in use).
User mmckenna recommended some great portable car antennas :
Larsen NMOWB450C UHF Wide Band 450-470MHz Mobile Antenna 35 1/2" w/Spring Base NMOQSPEC : Quarter Wave Omnidirectinal Whip Antenna
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
24,038
Location
I am a lineman for the county.
UHF is line of sight, so it's fairly easy to calculate.
That calculator will take the height of the antenna (make sure you select feet) and then tell you how far it is to the horizon. That'll give you a fairly accurate estimate. For the second radio, add its antenna height and add the two distances together.
Not perfect, but easy and gets you close.

For 25 feet up, you'll have about 11 miles line of sight. But figure in the height of the repeater antenna, and add that. Usually repeater sites use antennas that are high enough up to give them quite a bit of range. I'm betting 16 miles from the repeater may not be an issue if it's a good system.

For a base antenna, you can do better than Ed Fong.
It's important to understand that the antenna system is the most important part of your setup. You should invest in a good antenna and coaxial cable if you are serious about this.
Higher gain base antennas can work well since you don't have a lot of mountains around you.
When I was active on GMRS, I used a Laird base antenna.
Your coax cable needs to be chosen carefully and needs to consider the length of the cable run. -ALL- coax has some amount of loss. As length goes up, so does loss. The longer your cable run is, the more important it is to have a cable with low losses.

Since you are getting started, a few other things I'd recommend you take a very close look at before spending any money:
-Proper grounding of outdoor antennas is required by the National Electric Code. It's a safety thing. Some like to ignore safety. Sometimes they get lucky, sometimes they don't. Your choice.
-Just because you can program a frequency into a radio doesn't mean its legal, even if you have the right license. You should absolutely learn about, and fully understand, FCC type acceptance. Specifically how it applies to which radios you can use on which radio services. Just because some boob on the internets says it's OK doesn't mean it is.
-SHTF/Prepping and radios is only as good as your skill level. Everyone needs to know how to properly set up and use the equipment. Performance will be poor if the end users don't understand what they are doing, and wait until and emergency to try to make it all work.
-You've got a lot of people around you. In an emergency the radio spectrum may get crowded. Don't assume you'll have a repeater to yourself. Plan on that and have a backup plan. Then have a backup plan for your backup plan.
-Don't invest lots of money on low end Chinese radios. If you are serious about this, get the right gear, not the cheapest radios you can find. Those are a good starting place, but you don't want disappointment.
-Learning about radio means learning the rules and requirements also. Don't rush head first into all this and ignore the FCC. Part of being a skilled radio operator is knowing what you can and cannot legally do. Learn to do things right before assuming the rules don't matter.
 

Acorn12

Member
Joined
Feb 18, 2024
Messages
8
Thank you mmckenna! I am definitely the type to try and do things right, rules are there for a reason. A bit off topic but figured I'd mention this since you brought it up. When searching for a backup plan to a back up plan I recently learned about Meshtastic. Wondering what you think about this communication.

Do you think a yagi antenna will increase my reach?

Happy you told me about ed fongs antennas, I thought they were best in the game :).
 

merlin

Active Member
Joined
Jul 3, 2003
Messages
2,657
Location
DN32su
How much further will I reach with a roof antenna compared to a simple car roof antenna
The higher elevation will give you a bit more range for a given antenna.
Larsen NMOWB450C UHF Wide Band 450-470MHz Mobile Antenna
I have two of these, an older one with the open coil. tuned for the 462MHz region. has a good profile testing with a VNA and works great for GMRS. Considering adding it to my doscone mast on the roof.
The brand new one though, just won't tune and a terrible SWR across most of the UHF band
 

mmckenna

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Joined
Jul 27, 2005
Messages
24,038
Location
I am a lineman for the county.
Thank you mmckenna! I am definitely the type to try and do things right, rules are there for a reason. A bit off topic but figured I'd mention this since you brought it up. When searching for a backup plan to a back up plan I recently learned about Meshtastic. Wondering what you think about this communication.

It can certainly work if set up right. It's shared frequencies, so you gotta deal with everyone else that may be on there. Zero protections.

But what I meant by a backup plan was simple things you may already have:
Sometimes text messaging will get through when a phone call won't.
Most cell phones have a WiFi calling feature, and finding internet access may be possible.
Some newer cell phones can send text messages via satellite.
Devices like the Garmin InReach products that will send messages via satellite.

The "SHTF" thing usually isn't full, complete loss of all technology. Usually it's a minor inconvenience that a tech heavy population can't handle. Everyone has a cell phone and if they go down, it seems like people panic. Often they don't think to try WiFi, or a wired phone, or another carrier.
Sometimes the backup plan doesn't have to be super complex. It just needs to be a different way of looking at the problem.

Do you think a yagi antenna will increase my reach?

With UHF, line of sight, like I said. A Yagi will give you a directional signal which can be useful:
It can null out other stations you may not want to hear.
It can give a bit more power to get through urban clutter.
It can make a difference out on the fringes of coverage.
Since it's directional, you have to point it where you want to talk/hear.

Happy you told me about ed fongs antennas, I thought they were best in the game :).

He teaches RF and Electronics and they should be OK antennas. But they are not anything super fancy or ground breaking, at least not that I've seen. They are a basic antenna in a PVC pipe. You could probably make your own easily.
With base antennas, you need to consider the labor and cost to install. Ideally you don't want to climb up on the roof every year or so to replace it, so doing it right the first time can be much more cost effective, even if the antenna costs a bit more.
 

K4EET

Chaplain
Joined
Feb 18, 2015
Messages
2,214
Location
Severn, Maryland, USA
<snip> [Ed Fong] teaches RF and Electronics and they should be OK antennas. But they are not anything super fancy or ground breaking, at least not that I've seen. They are a basic antenna in a PVC pipe. You could probably make your own easily. <snip>
All statements right on. A friend of mine opened up a tri-band Ed Fong 2M/1.25M/70cm antenna that he has (and also loaned to me to test) and inside is just a simple “roll-up” J-Pole design. Test results were just like a homemade J-Pole antenna. Nothing more / nothing less…
 

nd5y

Member
Joined
Dec 19, 2002
Messages
11,351
Location
Wichita Falls, TX
This is also a nice LOS calculator:

Nope. It's useless exept for short paths because it only uses ground elevation and thinks the earth is flat.
 

K4EET

Chaplain
Joined
Feb 18, 2015
Messages
2,214
Location
Severn, Maryland, USA
Nope. It's useless exept for short paths because it only uses ground elevation and thinks the earth is flat.
I did not know that. Of course:

1. I’ve never seen the formulas used.
2. Professionally, we used different software packages for VHF/UHF/SHF and also surveyed all microwave PTP paths. As you probably already know, there are other factors to account for besides the earth being round. One factor, for example, would be taking into account the Fresnel zones along the path.
 

JustinWHT

Member
Joined
Apr 16, 2022
Messages
11
would be taking into account the Fresnel zones along the path.
First off... Two myths of Fresnel zones.
#1 - Structures or terrain with in any Fresnel zone will decrease your signal. Fresnel zone calculations are based on reflections, not based on obstructions. However using Fresnel zones plotted to Google Earth can give some insight of obstruction impact.

#2 a) Fresnel zones apply only to horizontally polarized signals (vertically polarized signals don't reflect off horizontal terrain).
b) The constructive in-phase interference is practically non-existent, but destructive 180° out of phase is significant.
c) Interference occures not only at 180°, but at 90° and 270°.
d) Fresnel calculations assume isotropic end-points, which do not exist in the real world of antennas.
e) The vertical beamwidth of a high gain antenna minimizes terrain reflections significantly.
f) Keep in mind that reflection inverts the phase 180°, that's why a mirror reflection is reversed.

Secondly - the 5/4th rule of radio wave propagating. The distance to horizon formula is √h x 1.22 = D, where h is in feet and D is distance in miles. 1.2 is a constant that reconciles feet and miles.
However radio waves are directed over and past the physical horizon by 5/4th added distance.
Therefore the correct formula would be
√h x 1.53 = D.
 
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