GMRS Repeater Antennas

[MR-EDACS]

Just wondering if any one has used a yagi such as a DB-436 on their repeater and possibly phased 2 of them together say one North and one South.

I cure have a Quantar setup As a repeater connected to a Yagi up about 120’ and getting about 15-20 miles of coverage on a portable. Now this antenna is facing due North and coverage to the South is about 5-6 miles which is to be expected since the tower is shielding it and the nature of the antenna. Was wondering if I should phase another yagi facing South instead of investment of a DB 420. This would make less likely to get damaged by Hurricanes since it not at the top of the tower. And since this is located down in South Miami I really don’t want go to far North and inter fear with other repeaters and users. Keep it local I guess.

Thoughts has anyone done this.

Thanks
John KF4ACN/ WRJG234

 

[prcguy]

When you split the feedline and feed another antenna pointing in a different direction the gain of both antennas will be reduced by about 3dB. The DB-436 is close to 10dBd gain and you would be dropping that down to a little less than 7dBd, why not just put up a 10dBd gain omni and enjoy good coverage in all directions? A 10dBd gain omni antenna will be a good 20ft tall and expensive, but they work really well.

 

[12dbsinad]

Since this is side mounted, a omni stick mounted to favor the south side of the tower would be ideal. The antenna may be more but you won't have to deal with phasing harness, and you would want to make sure the phasing harness is constructed of good quality coax suitable for full duplex operation.

Depending on how large the face of the tower is it will act as a reflector, you'll typically get less gain through the tower, so that would help with not wanting as much coverage up north.

 

[prcguy]

If you side mount and can get the antenna 4 or 6ft away from the tower it will be mostly omni directional. 4ft is two wavelengths and 6ft is three wavelengths at GMRS frequencies.

Since this is side mounted, a omni stick mounted to favor the south side of the tower would be ideal. The antenna may be more but you won't have to deal with phasing harness, and you would want to make sure the phasing harness is constructed of good quality coax suitable for full duplex operation.

Depending on how large the face of the tower is it will act as a reflector, you'll typically get less gain through the tower, so that would help with not wanting as much coverage up north.

 

[12dbsinad]

If you side mount and can get the antenna 4 or 6ft away from the tower it will be mostly omni directional. 4ft is two wavelengths and 6ft is three wavelengths at GMRS frequencies.

Yes, further away helps. It all depends on the tower and available loading. Putting the antenna at 6ft out puts a lot of twist on the tower. Not sure what the OP's structure is designed for.

 

[MR-EDACS]

Thank you for the comments

Unfortunately, the loading on the tower is high which will keep me from adding a DB420 at the top. Was just thinking since the Yagi antenna was working pretty good pointing North a phased one going South would take care of the South end. I do have a 3 DB omni antenna I could put in its place but will need to install a 4’ gate to support it. I have no interest in the East which is about 3 miles from ocean and West would put me about 8-10 mile from the everglade which could be covered by the side lobs.



Just curious if anyone has done this.



Thanks

John

 

[12dbsinad]

I've used phased yagi's before but not for repeater applications. In theory, it will work just fine. Just remember you will lose some gain. Since it's full duplex, I'd suggest a good quality fully welded yagi. You want everything tight with good mechanical connections, anything remotely loose will desence the repeater like crazy.. usually noticeable when it's windy. Also, make sure all coax/harness is of good quality without dissimilar metals, RG-214 type double shielded for harness,hardline for the feeder with size depending on length. NO LMR-400 type cable.