GMRS (mostly) base antenna question

[Guest mike]

Hi, I am interested in using GMRS frequencies, mostly simplex now & duplex in the future .  I'm also possibly interested in  2m/70cm ham bands in the future.  For now I will be using an HT connected to a base antenna.  I'm trying to find an appropriate base antenna (preferably a vertical)  which I can use for all the above with acceptable SWR.  And hopefully just do this antenna & coax thing once.  The repeaters are all close enough to me that I dont expect them to be an issue with any base antenna.  The trick is going to be using simplex.  As, I live in a small valley, and areas that I want to be able to simplex to outside that valley. Though they are mostly 5 miles or less, I expect it may be tough (also base on my trials with an HT).  I think the best I can do with mounting height is a 35 foot telescoping mast (which someone gave to me).  Oh yeah, I forgot to mention that I live in a hollow within that valley (if it sounds like southeast Tennessee , it is).  I have been researching antenna manufactures websites & many forums for the last several months, I have more knowledge than before I started, but still cant pick an antenna.  I have seen on several forums people stating that they use a 2m/70cm antenna (rated only up to 450mhz) & that they stall have SWR at or below 1:5.  The other issue is that I need to stay below $150.00 if possible.  Though if the perfect antenna for me was a little more, I would like to consider it.  I have read if you live in a hollow it may be best to pick an antenna which has a "higher angle of radiation) or "take off angle"  so, as to allow the signal to shoot over the surrounding hills , vs. bounce off them if the signal is shooting straight into the hills. So, possibly a plane vertical vs. a vertical with ground plane ?

thanks, Mike

[mbrun]

Hi, I am interested in using GMRS frequencies, mostly simplex now & duplex in the future . I'm also possibly interested in 2m/70cm ham bands in the future. For now I will be using an HT connected to a base antenna. I'm trying to find an appropriate base antenna (preferably a vertical) which I can use for all the above with acceptable SWR. And hopefully just do this antenna & coax thing once. The repeaters are all close enough to me that I dont expect them to be an issue with any base antenna. The trick is going to be using simplex. As, I live in a small valley, and areas that I want to be able to simplex to outside that valley. Though they are mostly 5 miles or less, I expect it may be tough (also base on my trials with an HT). I think the best I can do with mounting height is a 35 foot telescoping mast (which someone gave to me). Oh yeah, I forgot to mention that I live in a hollow within that valley (if it sounds like southeast Tennessee , it is). I have been researching antenna manufactures websites & many forums for the last several months, I have more knowledge than before I started, but still cant pick an antenna. I have seen on several forums people stating that they use a 2m/70cm antenna (rated only up to 450mhz) & that they stall have SWR at or below 1:5. The other issue is that I need to stay below $150.00 if possible. Though if the perfect antenna for me was a little more, I would like to consider it. I have read if you live in a hollow it may be best to pick an antenna which has a "higher angle of radiation) or "take off angle" so, as to allow the signal to shoot over the surrounding hills , vs. bounce off them if the signal is shooting straight into the hills. So, possibly a plane vertical vs. a vertical with ground plane ?

thanks, Mike

Hello Mike. Welcome to GMRS.

 

It is good to hear you are doing your research and you are getting some good information to help you make your decision.

 

If your antenna will live in a valley and you seek coverage on the valley floor and up the sides of the surrounding hills they you are going to want a low gain antenna, perhaps 2-4dBi. A home brew ground plane antenna is a candidate. You could also consider the Ed-Fong GMRS wire j-pole antenna (requires piece of plastic pipe and simple assembly on your end).

 

Before you even consider a broadband antenna you will want to know what the supported SWR limits are of the radio you intend to use. It is reported that some GMRS radios are not warranted above 1.5:1. This is certainly material if you are considering an antenna that could be used on amateur and GRMS frequencies. You could easily find SWR well over over 3:1 in the GMRS frequencies if using a dual band amateur radio antenna. You would have to test actually antenna units to verify.

 

You could look at discone antennas. These are low gain antennas with vary wide bandwidth for working big chunks of spectrum. Perhaps a discussion with the company ‘MFJ’ is in order to get their recommendation.

 

Personally, I would not complicate matters. I would focus on getting your self operating the way you want with GMRS first and worry about the amateur band and antenna separately.

 

Personally speaking, GMRS is primary for me so that antenna goes to the top of the mast. I have separate antennas and radios for each service.

 

 

Michael

WRHS965

KE8PLM

[Guest mike]

Michael, thanks for the detailed response.  So, are you saying that the lower dB gain antenna you have, the higher radiation or take off angle ?  Which will help me get over the ridges that are close to me.  If this is so, I realize I should have stated this in the first post, but :  I do live in a hollow the valley, however the two people that I will mostly talk with on simplex ( one is to the north & one is to the south ) , and the big ridges of the valley are to my east & west.  So, I think its possible that my coverage to the north  & south will be OK.   Also could that mean if I have a higher dB gain antenna , I would likely improve my north & south range vs. a low dB gain antenna, that would better get over the ridges to my east & west ? 

Also, the ed fong GMRS antenna : 

https://www.ebay.com/itm/GMRS-HAM-UHF-5dB-gain-Repeater-Base-Antenna-/112813555663

It looks like it is stating 5dB gain (mabe a good match for all directions / terrain I am dealing with ?  I like the price as well.  I think I will take you advise on just starting with GMRS antenna for my first antenna. 

Finally, I'm trying to figure out the best place to put mast & keep the coax run as short as I can.  I think it will be around 40-50 feet.  would you recommend a low loss coax & a quality brand & reputable supplier.  I have read enough on coax, to learn that this is not a good component to skimp on.

thanks, mike

 

[SUPERG900]

Michael, thanks for the detailed response.  So, are you saying that the lower dB gain antenna you have, the higher radiation or take off angle ?  Which will help me get over the ridges that are close to me.  If this is so, I realize I should have stated this in the first post, but :  I do live in a hollow the valley, however the two people that I will mostly talk with on simplex ( one is to the north & one is to the south ) , and the big ridges of the valley are to my east & west.  So, I think its possible that my coverage to the north  & south will be OK.   Also could that mean if I have a higher dB gain antenna , I would likely improve my north & south range vs. a low dB gain antenna, that would better get over the ridges to my east & west ? 

Also, the ed fong GMRS antenna : 

https://www.ebay.com/itm/GMRS-HAM-UHF-5dB-gain-Repeater-Base-Antenna-/112813555663

It looks like it is stating 5dB gain (mabe a good match for all directions / terrain I am dealing with ?  I like the price as well.  I think I will take you advise on just starting with GMRS antenna for my first antenna. 

Finally, I'm trying to figure out the best place to put mast & keep the coax run as short as I can.  I think it will be around 40-50 feet.  would you recommend a low loss coax & a quality brand & reputable supplier.  I have read enough on coax, to learn that this is not a good component to skimp on.

thanks, mike

 

 

The way antenna "gain" works is (in an omni, anyway) is by flattening it's vertical profile - less energy directed up or down means more energy directed "out". (Like squashing a beachball?)

 

This poses a problem for people living in valleys near a repeater located on a mountaintop - the repeater's signal passes right over them if the repeater's antenna gain is very high. So in the case of an omni antenna on a mountaintop - best not to overdo the antenna gain (if) the nearby valley(s) will be a problem. 

 

If you are *in* the valley - a super high gain antenna could prevent your signal from reaching upwards towards the repeater. 

 

Mostly - the higher gain antennas give you additional line-of-sight range, but if you're blocked, you're blocked.

 

I'm in a low foothill area and my HT *barely* makes it to a repeater just 6 miles away due to the blockage. Conversely, my base antenna, at 28 feet just rises above those hills. My base radio can not only hit that repeater 6 miles away, it can hit one 25 miles away on a mountain top  - full quieting - on just 1 watt.

 

I'm using a Diamond X-50A base VHF/UHF antenna - a rather ordinary beast, and it went for under $100.

[mbrun]

Good evening Mike.

 

“So, are you saying that the lower dB gain antenna you have, the higher radiation or take off angle ? “

 

No, not specifically. Gain has nothing to do directly with the pattern or “take off angle”. The angle(s) of radiation (or pattern) are a function of the antenna design. Antenna gain is a term used to compare the relative signal strength of one antenna relative to another at some defined relevant position.

 

A perfect omnidirectional antenna (does not exist in reality) radiates equally in all directions like a ball. This theoretical antenna has a gain of 0 dBi. This is called an isotropic antenna.

 

The simplest vertical antenna (a vertical dipole) radiates like a big fat round donut. This antenna type has a gain of 2.1 dBi. It achieve its additional gain by not radiating energy directly above and directly below the antenna and instead adds it into the big fat donut shape radiation pattern around the antenna. See Supergoo’s comment above regarding the balloon.

 

High gain vertical antennas achieve their high gain by robbing more and more of the power that would otherwise fill that big fat donut and putting it into a thinner and thinner and wider and wider donut. This is undesirable for you, because you want a fat donut to fill that hollow your are in, fat enough that it will radiate up the sides of the adjacent hills, rather than just at the foot of the hill.

 

If a specific antenna design your considering does have a higher “take off angle” and that angle aligns with the needs of your location that is fantastic. That would suggest that the antenna design favors/top-loads the donut (more power above the mounting plane of the antenna.)

 

You need to temper any expectations about getting over the ridges. GMRS frequencies do not roll very well over ridges. You may get over a little, but you will most certainly need a repeater up on the ridge to reach the other side well.

 

Based on what I know of your situation, I think the 5 dBi of the Ed-Fong about as high gain I would go for starters. Besides, it is an inexpensive investment to try. (BTW, I own and use two of his roll-up variety).

 

There are two things you do not want to skimp on in GMRS: Height and Coax. You need height to get the antenna above the obstacles that block (eat) your signal. But, the higher you have to go, the more signal gets lost in the coax.

 

I currently own LMR400 cable. Others use heliax hardline. LMR400 has about 2.7dB loss per 100’. That means that a 50 watt GMRS radio feeding 100’ of LMR400 cable will result in only approx 25 watts making it to the antenna, and only 2.5 watts will make it to antenna if you start with only 5 watts.

 

Finally, if you buy LMR400 make sure the manufacturer is Times Microwave. Do not buy any LMR-like imitations as I hear they are not even close to real LMR400 performance. I have no personal recommendation for heliax.

 

Good luck.

 

Michael, thanks for the detailed response. So, are you saying that the lower dB gain antenna you have, the higher radiation or take off angle ? Which will help me get over the ridges that are close to me. If this is so, I realize I should have stated this in the first post, but : I do live in a hollow the valley, however the two people that I will mostly talk with on simplex ( one is to the north & one is to the south ) , and the big ridges of the valley are to my east & west. So, I think its possible that my coverage to the north & south will be OK. Also could that mean if I have a higher dB gain antenna , I would likely improve my north & south range vs. a low dB gain antenna, that would better get over the ridges to my east & west ?

Also, the ed fong GMRS antenna...

It looks like it is stating 5dB gain (mabe a good match for all directions / terrain I am dealing with ? I like the price as well. I think I will take you advise on just starting with GMRS antenna for my first antenna.

Finally, I'm trying to figure out the best place to put mast & keep the coax run as short as I can. I think it will be around 40-50 feet. would you recommend a low loss coax & a quality brand & reputable supplier. I have read enough on coax, to learn that this is not a good component to skimp on.

thanks, mike

 

Michael

WRHS965

KE8PLM

[Guest Guest]

Thanks guys for all the good advise,  I will go with the Ed Fong DBJ-1 commercial antenna.  The beach ball & doughnut analogies really helped. 

[smalpierre]

Thanks guys for all the good advise,  I will go with the Ed Fong DBJ-1 commercial antenna.  The beach ball & doughnut analogies really helped. 

For my mobiles I use a moderate gain 2m / 70cm dual band antenna. I've seen that lower gain antennas also aren't as "tight" on the bands - they give you lower SWR just outside their designed for bands. Higher gain antennas seem to get low SWR only really close to their intended frequencies. So there's another +1 for a lower gain antenna if you're going to use a dual band instead of one tuned for GMRS frequencies.

[Guest mike]

smalpierre, that is excellent advise , I will keep that in mind in the future when I ham want to do more bands.   Thanks, mike

[Guest mike]

To:

Michael
WRHS965
KE8PLM

 

Michael, why do you prefer GMRS to HAM ?

[Guest Antenna Man]

In order to cover that much frequency range and still have a low enough SWR you will need to buy a discone type of antenna.

Something like the Diamond D130NJ would be best.

[wqxq281]

I'm using a Tram 1477 base antenna. It's less than 2:1 across 2M,440, MURS and GMRS.

[mbrun]

To:

Michael

WRHS965

KE8PLM

 

Michael, why do you prefer GMRS to HAM ?

It is not fair to say that I ‘prefer GRMS’ to ham. They are two radio services that exist for different purposes. GMRS is primary for me because of family. So as far as giving the GMRS antenna top position on the mast, it is because I want to give GMRS the best possible range for communicating simplex mobile/portable to home. In doing this, I know that I also achieve the best I can with local repeaters. Win-Win.

 

Amateur radio on the other hand is truly a hobby that fuels my interest in radio. It provides an avenue for experimentation and it connects me with other radio enthusiasts and the community.

 

Hope that answers your question.

 

 

Michael

WRHS965

KE8PLM