Batboard

Due to site congestion, I need to use a dual exposed bay UHF dipole antenna to support 2 UHF systems (a repeater & link radio).

Question: anyone have experience in using an Andrew/DB DB408-B below 450 MHz (440-450)? If so, what's the performance been like (i.e., SWR and radiating pattern)?

Also, anyone know what the isolation is between the two antennas?

Thanks.



Tony

railtrailbiker wrote:Due to site congestion, I need to use a dual exposed bay UHF dipole antenna to support 2 UHF systems (a repeater & link radio).

Question: anyone have experience in using an Andrew/DB DB408-B below 450 MHz (440-450)? If so, what's the performance been like (i.e., SWR and radiating pattern)?

Also, anyone know what the isolation is between the two antennas?

Thanks.



Tony

I ran a DB 420 for years at 443/448 with fantastic performance. TX SWR doing return loss on a Sitemaster showed about 1.4:1 at the 443 TX freq. I can't tell you about the pattern other than from about 400 ft ASL the coverage was virtually omni-directional. In flat Florida, that meant about 50 miles reliably to a 35 watt mobile with 5 dB gain roof mount antenna. Any of the exposed dipole antennas spec'ed for 450-470 from DB Products that I've tried have worked great out of band for me.

Isolation between the 2 is probably 20-30 dB since the total height of the thing is 9.5 feet. If you got 2 404's and vertically separated them more, you could get a lot more isolation....

Dave

There is a ham repeater around here that is using a DB224 (high band) with the radiating elements cut and lengthened by pieces of aluminum welded in, and a new phasing cable harness. It's ugly but I guess it works. For what it's worth.

Birken

railtrailbiker wrote:Question: anyone have experience in using an Andrew/DB DB408-B below 450 MHz (440-450)?
Tony

Coming from someone who has looked at the 'phase shift' on a vertical coaxial-colinear (stacked vertical half-wave coaxial elements) that is exhibited when operating them out-of-band, you're much better off with a 'corporate feed' (phasing harness style) where all elements are fed in-phase through essentially equal-length cables -

- Versus at just one end, and where the 'effective length' changes in the lengths of coax that make up that 'coaxial collinear' antenna.

While the match may be a little bad, at least the radiation pattern won't be so severely affected. (Also note that the BW of the co-co antennas is half that of the corporate-fed dipole arrays.)

Jim / WB5WPA

WPA6MDuplexer wrote:

railtrailbiker wrote:Question: anyone have experience in using an Andrew/DB DB408-B below 450 MHz (440-450)?
Tony

Coming from someone who has looked at the 'phase shift' on a vertical coaxial-colinear (stacked vertical half-wave coaxial elements) that is exhibited when operating them out-of-band, you're much better off with a 'corporate feed' (phasing harness style) where all elements are fed in-phase through essentially equal-length cables -

- Versus at just one end, and where the 'effective length' changes in the lengths of coax that make up that 'coaxial collinear' antenna.

While the match may be a little bad, at least the radiation pattern won't be so severely affected. (Also note that the BW of the co-co antennas is half that of the corporate-fed dipole arrays.)

Jim / WB5WPA

I can definitly agree with this in actual operating experience. Trying to use a Celwave Super Station Master out of band didn't work worth beans. Even the 450-460 banded one wouldn't cover the lower part of 440, the pattern was completely wacked out.