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Translator ERP question|?|

T

TomZ

I've searched in vain to find the antenna gain for a Shively 6812-3 Medium Power Circularly-Polarized FM Antenna. It's being fed 234 watts through ~114 meters of 7/8 heliax....

HAPPY NEW YEAR!
 
A two-bay CP antenna has slightly less than unity gain. A three-bay antenna would have a gain slightly less than 1.5.
Taking into account the line length, the combination of coax and antenna is probably close to unity.
 
Using 114 meters of Cablewave 7/8th air Heliax ( efficiency 72.85%), the ERP is 264 watts, assuming the antenna is mounted as a full-wave, with the listed 1.52 gain. If the cable is 7/8th foam, will mean a slightly lower ERP.
 
Checked the calculations--would be 258 watts. My program automatically entered the gain for the Shively antenna as 1.55, not 1.52. If 7/8th foam was used, minor difference, 257 watts ERP rounded.
 
Weird. What's up with that? I like the 6812 antenna but wonder whether a penetrator style antenna would be more effective for translators and LPFM's..
 
Better picture. Looks like it uses interbay line, so the angle of the first picture may be deceiving--that top bay may be connected. I would guess that the gain of the half wave spaced antenna would be closer to 1.3, which would then indicate the ERP is close to 220 watts.

The Shively website doesn't list gain figures for the half-wave configuration of this antenna.
 
What's the rung spacing on the ladder on the tower? Can you measure that at the base?

Not quite sure this is a 1/2 wave spaced antenna...
 
Remember seeing similar Shively antenna on the ground before it was installed for a B-1 station (11 kw ERP). Really tiny looking, especially compared with my 4 bay ERI (ERP 17 kw)
 
Tough to make a 100% call on this due to the angle. Remember that the zoom lens creates an effect that makes things look bigger than they appear... like when the batter looks giant compared to the pitcher when the zoom from center field is used.

Any way you can get a pic that's zoomed in but taken from farther back so the angle isn't as severe?
 
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