Was saying 1230w EIRP when I just looked
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Can anyone remember the reason B FM 88.7 (later 100.9) at Bankstown lost their licence?
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This media release from ACMA, courtesy of archive dot org, would explain why.
ACMA has had very significant concerns about the licenseeâs [2BCR] capacity to represent the interests of the Bankstown/Auburn community. Most of the licenseeâs members are from communities outside of the licence area and a significant proportion of its programs are directed at communities that are largely resident outside the licence area.
âACMA has concluded the licensee does not adequately meet the needs of the Bankstown/Auburn area â which is the purpose of the licence.
Source: ACMA MR 68/2007
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It does say that but EIRP is not the same as ERP.
The apparatus licence image is back up after it was issued a day âlateâ on Wednesday, seems to me pretty the same as what was discussed, including the 750W in the west-to-north quadrant (265° through north to 005°) and 75W to the more populated parts to the east and south, which⌠yeah, that full ERP would be pointing towards maybe Bilpin and Mount Wilson but not a heck of a lot else.
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And whether they are strictly adhering to those specs is another thing.
I know Great Lakes FM is supposed to be 500 watts to the south, but it seems to me that itâs still the max 10kw down here.
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There is some flexibility built into these ERP calculations, while it may say 750 watts, you would have some cable losses and nothing is ever 100% efficient. In the old ABA planning doc (still in use today) allows for +/- 2db for ERP, so in reality you might have almost double the ERP and still be within the rules.
Many of the commercial and community installations ive seen around the country, most have a stacked 4 bay mixed polarised antenna system with 3dbd gain, with a transmitter equal to the peak ERP allowed on the licence. I suspect, this extra 3dbd buffer allows for losses in the system.
Also many of the patterns on licences are almost impossible to reproduce in the real world, so a little wiggle room is needed.
Really???
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ERP is an Estimated calculation thatâs what the E in ERP stands for, it takes into account cable & combiner losses & antenna gain.
You calculate your ERP taking into account cable losses & antenna gain, then run the transmitter to the needed power level to achieve that ERP.
ERP canât be measured, itâs a theoretical calculation of radiated power, thatâs why thereâs a variation allowance in not being spot on ERP.
Thatâs because you lose 3dB on a mixed antenna over a linear Vertical or linear Horizontal antenna, if you have a 4 bay (for example) mixed antenna array that has a +3dB gain, then youâve negated that 3dB loss & have some extra gain as spare over the losses, so you donât have to run as big a transmitter power to get the ERP.
If you had a linear Vertical antenna, youâd in most cases only need a 2 bay array to achieve the same.
As an example, if you had a licence ERP of 10kW & used a 2 bay mixed polarisation antenna with a lower than 0dB gain or just over 0dB gain, also accounting for cable & combiner losses, youâd have to run the transmitter at or just over 10kW, to achieve that licence ERP of 10kW.
All antennas have different gain levels depending on the manufacturer & design, generally speaking a 2 bay mixed will get you 0dB gain, but sometimes a 3 bay will be needed, a 4 bay generally gives you enough positive gain to overcome losses in cables, combiners, etc. & then a little bit of spare.
4 bay mixed antennas wonât always give you +3dB gain though, itâs only a generalisation.
Generally speaking itâs a compromise between tower space, antenna gain, overcoming losses economically & transmitter power needs & costs, 4 bay mixed antenna array generally meets that well, thatâs why most stations use them in that configuration.
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EIRP (dB) = ERP (dB) + 2.15.
ERP = Effective Radiated Power. Many stations rely on just calculating the likely ERP. Variables can be difficult to accurately estimate in some cases, such as side mounted broadly omni-directional antenna systems being pattern influenced by the tower. Field measurements (drones etc) and range testing are tools to more accurately verify ERP.
In Australia, ERP has to stay within the licenced radiation mask. You are not allowed to knowingly exceed maximum ERP in any sector, for any reason.
I donât think so, though that would be nice to be allowed to turn up the transmitter another 3 dB!
Theoretical ERP is the output power of the transmitter, plus the gain of the antenna, minus the attenuation and losses incurred by feeder cables, combiners, connectors etc.
Itâs the same for vertical or mixed/circular polarised antenna systems.
If a station has a licenced max ERP of 10 kW and its 4 bay mixed pol antenna has a known gain of 3 dBd, then the antenna system input can not exceed 5 kW. In a case where system losses (combiner, feeder etc) are 1 dB, then running the transmitter at 10 kW would produce an ERP of 15.9 kW, 2 dB above its licenced maximum ERP.
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Was pleasantly surprised to hear âBefore the Worstâ by The Script on SWR 99.9 at 9:30am this morning. Itâs one of my favourite songs from the band, peaking at #10 on the ARIA Charts and being certified Platinum in 2009, thanks to them performing it live at that yearâs NRL Grand Final.
Then about 15 minutes later I heard âBreakevenâ on Wave 96.5 FM.
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No ERP canât be measured, any testing measurements as youâve put, are done in dBm or dBuV usually, there is a kind of conversion, but no itâs not accurate, ERP is in W or kW, measurements canât be done with any testing tools to give you an accurate power out of the antenna in W or kW other than being a theoretical calculation.
No, youâll lose 3dB on a mixed antenna as it has to radiate in 2 planes Vertical & Horizontal, & linear Vertical or Horizontal antenna only has to radiate in 1 plane & has a 3dB higher gain per antenna/bay over a mixed/circular one.
As a stacked array, the total gain for ERP calculations, yes, is the same for both liner & mixed, but you need to stack more antennas in a mixed array to overcome that 3dB youâre losing, otherwise youâll need a bigger transmitter power.
A mixed antenna is -3dBd per bay, but stacking increases gain, the point of stacking where you get 0dBd gain is the point of equalisation where youâve overcome the -3dBd gain for each antenna. Some antennas a 2 bay will achieve this, others need more bays. 4 bays wonât always get you a +3dB gain, you may need 6 for some mixed antennas.
You are right though, I mis-represented what I said & will edit the post, a 4 bay mixed antenna with a +3dB gain would only be allowed a 5kW transmit power for 10kW ERP.
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Yeah I know mate, was been a smart arse to old mate who assumed I didnât know what he was trying to tell me
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No worries. Was for anyone curious what the relationship was.
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2MBS FM, backup transmit antenna removed from the old Governor Phillip Tower Site now theyâve moved to TXA Artarmon.
Have to say Iâve never seen one like this before, very unusual.
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That looks like a helical. Circular polarised.
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Fantastic post all over @MrX.
Good idea, would like to see a return to a serious interrogation of whatâs proposed and who has the capacity to provide it. Beauty parade.
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Community radio related⌠such an awesome little community station, I remember the old studios in Wollongong⌠and the all famous cd wall 
This is the new site in unanderra, and wow what a setup.
Got a studio tour and some free stickers, some lovely elderly volunteers/presenters doing their show, great work⌠glad you found that INXS track you guys where looking for with the correct spelling 
We also managed to pick up BraidwoodFM going down Macquarie Pass⌠sounding pretty sweet with whatever processing yous got going on 
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Thanks for posting! Looks like a great set up!
Though Myswitch suggests that the Unanderra site doesnât have line of sight back to Brokers Nose, Iâm not sure how âgoodâ the location needs to be to ensure a reliable connection to the transmitter?
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