Yagi/J-Pole Antennas

[WRFX611]

I am new to GMRS so I apologize in advance for my ignorance. I was working on connecting to a local repeater (12 miles away per Google maps) and had no luck with the rubber antenna on my handheld. I have since purchased a 3 element Yagi and a BTech GMRS-50 mobile radio that I have setup as a base station at my house. I can hit the repeater just find and communicate with the Yagi. I have recently purchased a J-Pole antenna (has yet to arrive) to try and improve my omni-directional range and to possible bring with me on camping/hiking trips, etc to setup a mobile setup. My question is (assuming the J-pole alone does not hit the repeater) would it be possible for me to connect both the omnidirectional J-Pole and the Yagi to my radio at home? If so, how would I go about doing this and what types of things do I need to be concerned with as far as placement of the antennas next to each other and such. Currently I have the Yagi mounted in my attic (HOA is not very friendly and I don't want to ruffle feathers). Thanks in advance for any help!

[berkinet]

...would it be possible for me to connect both the omnidirectional J-Pole and the Yagi to my radio at home? If so, how would I go about doing this and what types of things do I need to be concerned with as far as placement of the antennas next to each other and such. ...

You could use both simultaneously. But, you'd need to split the signal while retaining a constant 50 ohm impedance to the radio. A duplexer (in reverse) might work. But, there is really no value in doing it this way and getting it tuned for optimal performance would be a nightmare.

 

You would be better off getting a remote controlled antenna switch (so you don't have two long cable runs) and using that to switch to the Yagi when you heard traffic on the J-Pole from the repeater. 

[Radioguy7268]

12 miles from a repeater with a J-pole should not be a problem. I think you'll be fine.

[Lscott]

My question is (assuming the J-pole alone does not hit the repeater) would it be possible for me to connect both the omnidirectional J-Pole and the Yagi to my radio at home? If so, how would I go about doing this and what types of things do I need to be concerned with as far as placement of the antennas next to each other and such. Currently I have the Yagi mounted in my attic (HOA is not very friendly and I don't want to ruffle feathers). Thanks in advance for any help!

You can do that. The two antennas need to be separated by around 5 to 10 wave lengths to keep the interaction to a minimum. That would be around 10 to 20 feet approximately.

 

You can't connect the two antennas to the radio electrically at the same time. One the impedance match will be all wrong. Second with both antennas radiating the "pattern" will be all messed up. You will have strange max signals in some directions and very low in other directions. The Yagi is designed with the extra elements on the boom, and no others close by, positioned and cut to a specific length to generate the maximum signal strength in a direction along the length of the antenna.

 

You can connect the two antennas, one at a time to the radio of course. The easiest way would be using a two position coax switch. You have one port that goes to the radio while the other two, one each, goes to the separate antennas. All you need to do is flip the switch to select one or the other thus no cable swapping required.

 

If you do use a coax switch be sure to get one rated up to UHF. The cheap HF ones using the SO-239 solid filed connectors ones will cause elevated SWR. The best type are the ones using "N" type connectors.

 

https://mfjenterprises.com/collections/switch/products/mfj-2702

 

You would be looking for the model "MFJ-2702N".

 

https://store2.rlham.com/shop/catalog/advanced_search_result.php?keywords=MFJ-2702N&osCsid=mi2iq1vl96t07d35go4eai6e32&x=0&y=0&search_in_description=1

 

If possible all your antennas and cables should be using "N" type connectors where you can. The SO-239/PL-259 types can lead to higher SWR than expected. The "N" type will minimize this.  Sometimes you can't help it if there are SO-239 types, typically on mobile or base radios. In those cases you will need to use adapters.

 

Some will claim that adapters have high losses, power. Good quality ones don't. One or two in line and you'll hardly even notice the difference. If you mount everything in your attic you really don't have to worry about water ingress into the cables or adapters.

 

A word about attic mount antennas. If you have foil back isolation and or asphalt shingles this could cause high SWR in the first case, metal in close proximity to the antenna, and lower radiated power and received signal strength in the second from absorption by the asphalt. 

 

A Yagi used for FM needs to be mounted so all the elements are vertical NOT horizontal. Almost all communication on the GMRS band uses antennas vertically mounted. If you mount the antenna the wrong way the signal at the receiving station can be significantly reduced. Also your received will be much lower as well. 

 

To mount the Yagi vertically you should use a nonmetallic mast. A metal one could seriously degrade any benefit you get from using a Yagi.    

[FlightInWinter]

Fantastic information on yagi mounting and switching. Thank you!

I am currently awaiting delivery of a KCØSDV dual band collapsible J Pole antenna for omni-directional coverage and I am looking to install a yagi so that I can reach a repeater about 50-ish miles away. Currently 5 watts output but I will probably change that soon.

Any recommendations on what antenna I might be looking for? 
No HOA rules and no zoning so I can do whatever I want or need to do.

[Lscott]

When looking at an antenna system you need to consider at least two things, coax loss and your antenna gain.

 

At UHF coax loss can be rather high for the typical type most people tend to use. It's a trade off between cost and cable loss. Less cable loss the bigger and more extensive the coax will be. I see many going for LMR-400. The loss at 450 MHz, GMRS is 462 MHz to 468 MHz approximately so we're close enough for this example, is 2.7 db per 100 feet. So if you have a 30 to 40 foot high tower or mast on the house you could easily use 75 feet of cable from the antenna to the radio. That works out to 2.03 db of loss so only 63 percent of your transmit power makes it to the antenna! What you would like to do is pick an antenna that has enough gain to make up, so to speak, for the cable losses at a minimum.

 

A quick note here on gain, or loss, of  every 3 db represents an increase by a factor of two, or a loss by 1/2. So a gain, or loss, of 6 db would be an increase by a factor 4, or a loss by a factor of 1/4. 

 

Now we have some things to look at very carefully with antennas. You will see antenna gains shown as some gain followed by "dbi" or "dbd". If it isn't shown or mentioned it's most likely in "dbi". The two gain spec's are NOT the same. The gain spec'd as "dbi" is the gain above a theoretical and impossible to build isotropic antenna. The gain spec'd as "dbd" is the gain above a dipole, really amounts to a 1/4 wave antenna on a ground plane. Think a cheap 1/4 wave magnet mount.

 

The gain in "dbd" for a dipole is 0 while using "dbi" it's 2.15. Remember this is exactly the same antenna! Manufactures like to use the "dbi" spec because it inflates the gain by a couple of db. If you're not paying attention a cheap antenna rated in "dbi" may appear to be as good as a more expensive one rated in "dbd". Dishonest, no, but you need to be educated about what the spec's mean to make a good purchasing decision. So for example you might see a 1/4 wave antenna spec'd as 2.1 dbi. Hummm...

 

Now getting back to the issue with cable loss you need a real gain of at least 2 dbd just to break even due to coax losses in the above example. Ideally you would like a lot more. Of course the antenna will be larger, longer, and more expensive. As the gain increases, it's usually at a spec'd center frequency, as you depart from that ideal point the gain tends to drop off. You want one designed and tuned close to center of the band of frequencies you want to operate on. In you case around 467 MHz to 468 MHz which are the repeater input frequencies for GMRS. 

 

I'm sure some members here have good recommendations. Also search past posts on the forums here for info.    

[FlightInWinter]

Excellent info, thank you.

I am looking to use 75-feet of LMR-400 coax and have my eye on a 6-element Browning BR-6356 450-470Mhz yagi rated at a 10.2 dBd gain.

I have serious doubts that 5-watts will make the trip to the repeater 50-ish miles north of us even with a fairly decent antenna. Am I right?

[berkinet]

...I have serious doubts that 5-watts will make the trip to the repeater 50-ish miles north of us even with a fairly decent antenna. Am I right?

It really all depends. Key factors are the terrain between you and the repeater, the length of your coax line, and the quality of your receiver. But, honestly if you can make it with 50 wants you stand a pretty good chance of making it with five.

[Lscott]

I have serious doubts that 5-watts will make the trip to the repeater 50-ish miles north of us even with a fairly decent antenna. Am I right?

You can go to this site and experiment with putting in different heights for the antennas.

 

http://www.hamuniverse.com/lineofsightcalculator.html

 

The resulting range is just an "estimate" of what you're likely to get. There are a number of hard to define factors that also figure into range calculations. So take what you see with a grain of salt.

[FlightInWinter]

Based on the information on the site with the distance calculator, I am beginning to seriously doubt that I can reach that GMRS repeater up in town due to line of sight constraints. I'd have to have a VERY tall tower.
A man's got to respect technology's limitations.  I'll do what I can and maybe the winds of favor will blow in my direction.
Thank you for your assistance in helping sort this out.

[Lscott]

Based on the information on the site with the distance calculator, I am beginning to seriously doubt that I can reach that GMRS repeater up in town due to line of sight constraints.

That's likely very true. I'm in the Detroit area and there is a wide coverage area linked repeater, UHF - VHF, on top of the tallest building around, the GM head quarters building. The antennas are up at 728 feet. You might get into the repeater at 40 miles more or less. That should give you some idea.

 

 http://www.gmarc.org/wp/

 

This is the estimated UHF coverage zone map.

 

http://www.gmarc.org/wp/uhf-repeater-coverage/

 

And this is the estimated VHF coverage zone map.

 

http://www.gmarc.org/wp/vhf-repeater-coverage/