Hi All,

I think most of you are aware that I volunteer at a local Community FM radio station.

AND as with most Community stations we have bugger all test gear and we have had our 500W PA repaired under warranty and am about to put it back into the rack.
However before I do that I need to check the 30W Exciter Deviation that with what the audio level is coming IS in fact giving us the correct Deviation as it was MOST noticeable that when we switched to our 100W Standby TX the audio quality was FAR better than we had been hearing on the Main TX.

I am suspicious that when many moons ago the transmitter was moved to a new location and was then fed via a Codec (Tieline Bridge-It) via the Internet from the studios 3kms away that the L & R audio coming off the Codec was NOT +4dbm as it was when the TX was in the back yard of the old studios.
The Exciter DOES have a Deviation meter of sorts on it but there are doubts about its accuracy and I went chasing a Heathkit IM4180 and found one on flea bay but missed it by around 3 hours.

The Heathkit IM4180 is supposedly quite good and the station is willing to pay up to around $150 for a good one but I am hoping that someone in WA if at all possible has one that I can borrow if not for sale so I can run the Exciter in a dummy load and take a sniff of the RF and pop that into the Heathkit meter and prove without doubt that we ARE getting correct L & R levels going into the Exciter.
IF it is down then there is a gain pot within the Exciter I can tweak to give us the correct 75kHz Deviation.

Then and only then will I set the PA back up on air and reset that to give us the 200W ERP we are currently allowed and we should then have a much better audio sound than we ever had previously after the TX was shifted.

Anyone able to help??

Lindsay

Lindsay
Is there an ABC transmitter on air close by? They used to be pretty spot on deviation wise. You could wing it by ear, adjust your audio levels to be similar should get you in the ballpark. (ive had to do that in a previous life)

Over modulation will make you sound louder but theres a diminishing return, It will start to sound muffled

Most commercial stations push the limits deviation wise and use compression too.

Unfortunately I dont have any broadcast gear anymore

cheers
Ben

If you can’t get your hands on a deviation meter, then this alternative method might be adaptable to your situation:

https://www.youtube.com/watch?v=8IBOYoIV5m8

Tks for replies so far.

Ben, There IS a large ABC FM TX nearby running 100Kw but it is their classical station so rather different to what KCR pumps out being almost every genre as each Presenter uses their own music. Thus a vastly different sound to us.

GTC, Yep am aware of the Bessell function method but apparently it is quite slow to do as the carrier nulls are easy to miss.

I DO have a Field Strength meter (Ikusi T80) but am not entirely sure of how narrow the tuning is on it.

If I cannot locate a Heath Kit IM 4180 I might have to use the Ikusi and also observe the Exciter's inbuilt Deviation display (its just a series of LEDS in an arc) and see what the Ikusi shows when the Exciter meter shows 75% using the applicable input tone to observe a Null in the carrier..might work.

No real hurry right now as that will be the next project once I get the two new studios setup and functioning which will take me a few weeks once the desk tops arrive and we can instal them on the frames and set about putting the new mixing consoles in place and getting all the audio levels correct end to end.
Then migrate needed stuff to the new rack and dive into a cutover.

Lindsay

An update.

Have sourced the use of a VG Marconi TF2033 (I think it is) and have been able to sort out the Deviation issue so on Sunday we go off air for a while so we can re-align the studio to TX path and then reset the Deviation settings and once done instal the repaired 500W PA and get us back onto our Main TX.
Hopefully we sound as good as we currently do just running on the 100W Standby TX which is showing 75% Deviation on its inbuilt metering.
Lindsay