Looking for great uhf nmo antenna

[N4KVE]

I used to live in Miami Florida, but moved 60 miles north to Palm Beach. While I use the local repeaters here, I still try to keep in touch with a few friends in Miami using the repeater down south. I use a 100 watt amp, had a preamp installed in my radio, but I just need a little more umph. I basically use UHF, but I have been using a Diamond 770NMO, & a 7200, as well as a Larson dual bander. The Diamonds claim 5.5 db, & the Larsom 3.5 db, but they all sound the same. If I'm 10 miles south in Lake Worth, the repeaters all come in great. So is there an antenna even if just UHF, about 40" that will work better than the antennas I am using? I'm using a trunk lip mount ant base with only 4' of RG-58 cable because the radio sits in the trunk, with the control head up front. 4 or 5 different radios give the same results. Any suggestions? GARY N4KVE

 

[davidgcet]

60 miles on a UHF mobile is asking a lot unless the repeater is high up in the air with a good antenna. one of our old community repeaters is a hair over 50 miles from our office. it is on top of a 300' tower on a 200' hill and i am in flat lands with nothing between and can't hit it with a mobile in a truck unless i drive 2 miles closer and get out of town, then it is crystal clear. remember that UHF is LOS and does not follow the earth curvature.

putting your antenna on the roof my help, but whether it will actually help enough or not is a debatable.

 

[N4KVE]

The rptr is actually at the 800' level on a 1000' TV tower. There are several remote receiver sites, & 1 is closer to me, so I have no problem getting into the rptr. Just hearing it the last 10 miles, & some days are better than others. I just thought maybe there was a US made commercial antenna that would be better than the Diamond I am using. Maybe I'm just asking too much. GARY N4KVE

 

[popnokick]

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Have you put an SWR meter that is rated for the 70cm/440 mHz band online from your radio to your antenna to check your SWR? And after you do that, try a newly made coax cable that is a slightly different length than your current coax - say about 4.5 feet. See if these simple tests and changes reveal anything.

 

[W2NJS]

Rptr access problems...

Gary: Is it possible that the repeater's tower antenna is on the "wrong" side of the tower to cover your location? Up here we recently relocated a VHF, not UHF, repeater and had the dipoles put on the side of the tower that faces away from DC instead of toward downtown. Results downtown now leave a lot to be desired, but "upcountry" out to 30/40 miles the thing is DFQ, which does most of us no good at all. Other than that the only possible thing that pops to mind, as was already suggested, is that you might have a resonant feed line (quite possible with four feet of coax and a UHF system).

Regards,

Tom, W2NJS

 

[N4KVE]

Gary: Is it possible that the repeater's tower antenna is on the "wrong" side of the tower to cover your location? Up here we recently relocated a VHF, not UHF, repeater and had the dipoles put on the side of the tower that faces away from DC instead of toward downtown. Results downtown now leave a lot to be desired, but "upcountry" out to 30/40 miles the thing is DFQ, which does most of us no good at all. Other than that the only possible thing that pops to mind, as was already suggested, is that you might have a resonant feed line (quite possible with four feet of coax and a UHF system).

Regards,

Tom, W2NJS

Hi Tom. Let me clarify what I exactly have. I'm using a UHF MTS2000 in a Convertacom. So there's 8 ft RG8X going from the cradle up front, to a 100 watt TPL amp in the trunk. From the TPL, it's 4 ft of RG58U to the antenna. I have no trouble transmitting to the repeater, & on anything within 20-25 miles, I turn the amp off & use 4 watts. Before that I was using a 438-470 Spectra with a factory preamp. 2 ft coax from the radio to the amp, & 4 ft from the amp to the antenna. Basically the Spectra, & Jedi sound the same on RX. Next week I'll be installing a 100 watt MCS2000, so out comes the amp, & it's just 4 ft coax from the radio to the antenna. Maybe I'll gain a little by removing the amp from the equation? Today I rigged up 3 cooling fans & a shroud to keep that radio running cool. Lo power is 60 watts. Even if the short coax messed up the SWR, would that mess up the receive? And remember, once I drive 10 miles south & am 50 miles from the repeater, it sounds great. That's why I think I might be asking too much. GARY N4KVE

 

[mrweather]

Going from 2' of coax to 8' of coax will have no effect. The amp may be introducing some loss but I wouldn't worry about it. A mismatched antenna will have an effect on reception but only if it's really off the scale.

The Larsen is an excellent antenna. Just a suggestion: UHF is very line-of-sight. If you could mount the antenna on the roof of your vehicle I think you'll notice an improvement. A) it's the highest point on the vehicle, and B) the groundplane is bigger and better.

I higher gain antenna will "squish" the transmitted signal more towards the horizon. In Florida that's probably a good thing! Larsen makes a single-band UHF gain antenna: the NMO440C which is about 33" tall and is advertised to have 5.6 dBi gain. I've never used it but if it's like the other Larsen antennas I have it will be decent.

 

[N4KVE]

I installed the MCS2000, & the rx actually improved. The TPL amp was removed which also meant 2 less coax connectors in the line. Good deal. GARY N4KVE