new frequency old antenna rfs super station master

[KitN1MCC]

well i just got my new Repeater frequency from from PCIA and the output is 152.30 my old base frequency 159.855 (changed to mobile only) and the antenna i have is rated for 155-163 do you thin it will perform well at 152 or should i invest in a new antenna.

[Bill_G]

In general, the higher the gain, the tighter the skirt. But, it's worth a try. A wattmeter will tell you if the vswr is good, and an Anritsu return loss will tell you how steep the roll off is on the low end. Most people have access to a wattmeter. You might have to weigh the cost of an antenna against the cost of a tech to sweep your original with a return loss test.

[Tom in D.C.]

Look up the bandwidth specifications as stated by the manufacturer on the internet. That will tell the complete story.

[KitN1MCC]

lucky were i used to work i am still freindly with them i am gonna see if they can do a sweep. i may hook up a antenna analyzer too

[xmo]

I recommend that you replace the antenna.

There is more to consider than return loss.

If the existing antenna were an exposed element type such as a DB224, you might find the performance acceptable at your new frequency but with the typical fiberglass collinear - probably not.

The difference is that the exposed element antennas utilize a true "corporate feed" phasing harness. Thus when the antenna is operated away from the frequency it is cut for, even though the phasing harness sections are not the optimum length and the match degrades, they are still identical in length and therefore the antenna elements are still fed in phase.

On the other hand, the typical fiberglass gain antenna uses a sequential collinear feed, thus when such an antenna is operated away from the frequency it is cut for, the elements are fed out of phase.

Why does that matter? If the antenna elements are fed progressively out of phase, the antenna pattern tilts up or down [out of phase feed is exactly how an electrical down-tilt antenna operates].

How much difference does that make? I once had an opportunity to put a 2 meter repeater at a site that had two existing VHF antennas cut for 155 MHz, but only one was in use - the other was offered. One antenna was a DB224, the other a fiberglass collinear - both the same gain and both at the same height.

I went to several sites 2 to 4 miles from the tower - sites with broadband test antennas available, and measured the signal level received from the 155 MHz system - first with one antenna, then with the other. The signal levels were identical in every case.

I repeated the test with a 145 transmitter on each antenna. The signal levels at 145 on the DB224 were virtually the same as the 155 signal levels had been but when the 145 system was operated on the collinear - the signal level was down 10 dB or more everywhere.

[KitN1MCC]

yeah i may just order a new one. is there any place other than tessco to order RFS stuff there plant is 10miles from the Site just not sure who to call