Mounting Base Antenna Upside Down

[rescuer]

Ok, OK...Don't laugh. What negative aspects would there be to mounting a base antenna upside down? Would a 10' antenna mounted upside down at 50' perform the same as the same antenna mounted the correct way at 40'? The reason I ask is could I make a standoff antenna mount for a tower in which I could have two antennas on one mount (one up, one down, but not touching each other. The frequency difference would be approximately 2.75 MHz apart (VHF-High).

Should I just forget it and use two seperate mounts? It so, could I mount them at the same height?

Thanks,

[tvsjr]

There's nothing wrong with doing that. My RACES repeater is on a DB264 mounted hanging down off the candelabra. A DB228 is nothing more than two DB224s stacked... even available in split-harness for RX/TX antennas.

Just make sure the antenna is rated for mounting in that direction (some cheap antennas will likely fill up with water).

What type of antenna are you trying to mount?

[440roadrunner]

The answer is NOT a qualified yes

Some antennas have issues with drain holes and weather covers for loading/phasing elements.

Some antennas have downtilt built in, and in the case of loop dipole designs like the DB224 and related series, this is done by playing with phasing harness lengths.

Just because it "looks" the same does not mean that it is.


Best way, is to simply contact the guy who built the antenna



Ok, I think I misunderstood your meaning. You don't want to MOUNT AN ANTENNA UPSIDE DOWN, you want to mount the antenna by HANGING IT from the TOP OF THE ANTENNA is that correct?


However, once again it depends on the antenna, and since you didn't specify what that antenna is..............

[Bob W]

....The frequency difference would be approximately 2.75 MHz apart (VHF-High).

Should I just forget it and use two seperate mounts? It so, could I mount them at the same height?......

Another issue is: What are you trying to accomplish with the two antennas. If you were to say a VHF, and a UHF, then that kind of isolation between the two antennas would be fine. In the case of two antennas on the same band, there's really not much isolation between them with the vertical spacing you are talking about. Hearing on one and transmitting on the other with the 3 MHz split is out unless you start talking about using cans. Depending on transmit power, it could be hazardous for the receiver, even more so if I understood that you might be mounting them at the same level looking at each other.

By 10 foot antenna, are you talking about something along the lines of a Diamond antenna? If so, they will fill with water if inverted unless you come up with some kind of hood for the connector end that will now be facing up. You will also need to figure out how to get the downward facing tip to breath so the condensed moisture can drain.

[bernie]

My two bits worth:
"Inverted mounting"
There are even special mounts for just this purpose.

If the antenna was not intended for inverted mounting it will eventually fill with water and fail.

Look up the model number in the manufacturer's catalog to see if it is invertable.

[AEC]

Inverted mounting serves only one thing....NULL FILL.

The main lobe of the anenna would be favoring the nearby ground and not on the horizon as it should be, not taking into account any electrical or mechanical downtilting of course.

Inverted mounting will get you limited range, but great coverage close to the site.

Cellular sites used that technique for years due to site locating near highways, when vehicles are passing by the tower, they would drop out, only to 'reappear' a few seconds later, far enough away from the tower so the main antennas could 'hear' the mobile uplink.

This is why one antenna was inverted, and that was its only purpose as well.