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Will a 3 bay ERI (1991 vintage) on 96.3 work on 95.9?

A

artsutton

We have a 3 bay ERI antenna (1991 vintage) on 96.3. I need to get a Class A on 95.9 on the air cheap. What are the chances that the 96.3 would work ok on 95.9? When you talk to the antenna manufacturer they want several thousand to do the change plus have to ship it to them and back, etc.

Wish I knew the model number but was installed by previous operator. It doesnt have deicers or radomes.
 
It will work but the efficiency won't be good. Excessive reflected power and incidental amplitude modulation.
It really should be re-tuned to the new frequency.
 
Art...is it a Rototiller style antenna, or the 1105 ring style? The Rototiller will likely be more difficult to field adjust.

An engineer with a network analyzer should be able to check the antenna for you and predict how it will perform on 95.9. My guess is that you will be unhappy with the results and end up purchasing a new one.
 
The antenna may not even be legal as it won't meet the factory published specs for antenna gain, etc.
It will need to be re-certified after it is tuned to the new frequency.
 
This is a frequency change of only 0.4%, so the changes in gain and pattern shape would be insignificantly different than for 96.3 -- assuming this antenna wasn't used for a directional licensee on 96.3. Omni ERI rototillers have been diplexed for operation on frequencies quite a bit more separated than that.

Chances are high that if it was working properly when last in service, was disassembled and stored properly, was reassembled properly on the new support, and its input impedance match to the line was optimized then -- it would be just fine.

You may have to provide different mounts for it to accommodate the new structure.

ERI should be willing to endorse this change without requiring a factory re-build, and supply their official statement of its gain for this change in frequency -- if it is thought to be significant enough to worry about.
 
If it's a rototiller type, they are fairly broadbanded. Usually, they are about 2mHz wide, so the minor mistune should be barely noticable. Run a simple test: load an exciter into it and check the VSWR.
 
I think it will work just fine. The slugs in the transformer will likely need to be adjusted, but otherwise all should be well.
 
I've run a 102.7 one on 103.1 with minimal adjustment. Either fire up an exciter into it or if you have an MFJ analyzer, you can see what's going on. Agreed that the tuning slugs may have to be touched up.
 
If your lucky enough to find someone with a Power Aim 120 the tune-up job, if not in a really dense RF enviroment, becomes very easy. If you have a spectrum analyzer/service monitor with a tracking generator and an outboard 3-port return loss bridge, you can likely tune around on it too. http://www.eagle-1st.com/eagle1st.nsf/10201000!OpenFrameSet
 
I've run 97.9 on a 2-bay ERI that was put up for 93.1. VSWR was very acceptable.

The only difficulty was that the chains on the ol' McMartin PA tuning kept falling off cranking it between 92.3 & 97.9.
 
6 bay half wave rototiller on 100.3. Changed the transmitter to 102.9 and fired it up. Over 3KW forward and 4 watts reflected. It will probably surprise you.
 
Antennas are not as tight speced as they would like you to believe.
 
ERI makes 3 antennas for the Fm band. I ahve made similar small changes in frequency and it worked well. I ahve to recall that the tuning is normally not for center frequency but a channel down so that when icing occurs it tunes in before adding reflected power. Chances are it is tuned to 96.1 in reality.

Don't try this with a BKG 88 or similar. THye ahve to be tuned for exact frequency. Has to do with the size of the elements and being less broadband.
 
ChiefEngineer said:
I ahve to recall that the tuning is normally not for center frequency but a channel down so that when icing occurs it tunes in before adding reflected power. Chances are it is tuned to 96.1 in reality.
Click to expand...
Actually, they are tuned 1 channel high so that when the ice forms on it, the size increases and the resonant frequency drops. If it was a 96.3 antenna, it was probably set for 96.5. I still think it will pleasantly surprise you.
 
BobOnTheJob said:
ChiefEngineer said:
I ahve to recall that the tuning is normally not for center frequency but a channel down so that when icing occurs it tunes in before adding reflected power. Chances are it is tuned to 96.1 in reality.
Click to expand...
Actually, they are tuned 1 channel high so that when the ice forms on it, the size increases and the resonant frequency drops. If it was a 96.3 antenna, it was probably set for 96.5. I still think it will pleasantly surprise you.
Click to expand...


Yep. Good chance it will be acceptable and not need tuning. Especially if it's one of the high powered ones- which are more wide banded than the lower power ones.

I've seen them work 3.5 MHZ from the original frequency and have pretty reasonable VSWR.
 
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