swr's and antennas

bayfire300 · Post by **bayfire300** » Sat Mar 11, 2006 2:04 pm

hello everyone.......will swr's change drastically w/ a ham antenna from uhf ham bands to gmrs?
i have a gnrs repeater using a ham antenna and cant get the swr's down... ita at 6:1 now and te performance really stinks
the cable lenght is 20 feet
if i get a commercial antenna 460-470 you think that will help alot?

thanks
otto

n2knc · Post by **n2knc** » Sat Mar 11, 2006 3:02 pm

bayfire300 wrote: gnrs

u mean G.M.R.S. ?

bayfire300 · Post by **bayfire300** » Sat Mar 11, 2006 3:07 pm

yea typo.......it happens

n2knc · Post by **n2knc** » Sat Mar 11, 2006 3:11 pm

i would try a antenna made for that band(gmrs) or try to tune the one you have if there is a way, is there anyway u can cut it down to make it any better??? some times if its stainless steel cutting 1/4 of a inch off helps

RadioSouth · Post by **RadioSouth** » Sat Mar 11, 2006 4:34 pm

6:1 ! I hope you've taken it off the air, definetely enough reflected RF to damage the transmitter. What is the SWR of the antenna within it's rated bandsplit ? Sounds very high, might have other factors at play.

bayfire300 · Post by **bayfire300** » Sat Mar 11, 2006 5:10 pm

it's a ham 2m/70cm antenna but when i use my vhf repeater w/ same antenna and feedline at 158 mhz swr's are fine.
yea i took it off the air.i'm gonna get a commercial antenna and try it then
aslo i'm gonna reprogram radios to ham band to see what the swr's are then ....if still high itts gotta be the antenna
thanks
otto

tvsjr · Post by **tvsjr** » Sat Mar 11, 2006 7:20 pm

It's a piece of :o ham antenna. The SWR is likely high in the ham bands, higher still anywhere else.

Get something on the order of a DB408 cut for your particular licensed channel and it'll work properly.

Consider a Sitemaster or a spectrum analyzer/tracking generator with a return loss bridge to check your results before connecting up your repeater... 6:1 is high enough to toast a repeater (especially a cheap one that doesn't fold back well) in a hurry.

wa2zdy · Post by **wa2zdy** » Sun Mar 12, 2006 6:40 am

The dualband antennas don't work too well outside the ham bands, that is if the swr is even where it should be in the ham band.

Otherwise a single band UHF antenna will work "ok" between the 440 ham band and GMRS. I used a Larsen NMO44B collinear on the roof of my truck for both without significant issues.

But for a repeater, why cut corners? You've already made a considerable investment if you've done it right, so the most important part of the system isn't the place to skimp.

As others have said, get a real repeater antenna, tuned for the band. Even a decent quality base antenna might not be satisfactory for a repeater. Those involved commercially will be better able to tell you which antennas to avoid for repeater service. And which are good, like tvsjr just did above.

bayfire300 · Post by **bayfire300** » Sun Mar 12, 2006 8:58 am

i ordered a uhf antenna 460-470 and some heliax....i hope that does it.
the repeater is 2 radius's w/ a rick unit ...antenna not very high i just use it for friends and family around town. but either way i can't have those swr's so high......i think the new antenna and heliax will do the trick ......i'll let you all know how it turns out
thanks for all your help i appreciate it

otto

swr's and antennas

swr's and antennas

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