Friday, December 30, 2005 - 11:38 am, by: Anthony Wah Day(Naastee)
Hey guys and gals
Was woundering if anyone could answer this question for me. Brought a brand new Deck for my car, but the sales guy said that i might not need an fm expander?? I know this guy well and trust his judgement but i am just wanting to get the truth from people who have actully done their own.
Friday, December 30, 2005 - 11:51 am, by: Matthew Oswald(Matt)
Anthony,
Just a few days ago, i installed my new deck. I get the feeling i have an FM expander, because on my stock headunit, my radio was showing 83.7MHz for Nova (93.7MHz)
Now with my alpine deck in, it tunes best into Nova with 103.7MHz. I get the feeling that you shouldn't need the expanders with your new head unit.
Friday, December 30, 2005 - 12:29 pm, by: Jason Kingsmill(Jason_k)
With an aftermarket Australian deck, you do NOT need the expanders.
The expanders are used to lower the frequency of received signals so they are in the band that Japanese tuners can receive.
In an aussie tuner, it is tuning for the correct frequencies, so adding a band expander will actually put the transmitted signal out of range.
Matthew, I don't know how you can pick that signal at all, as it should still be lowering the frequency to 83.7MHz(out of range). Maybe some form of signal ghosting?
Friday, December 30, 2005 - 02:36 pm, by: Mark Paddick(Sparks)
It's a simple superheterodyne mixer. You will get products in the output of Fo +/- the expander frequency and Fo + (2 x (+/- the expander frequency)) and Fo + (3 x (+/- the expander frequency)) and Fo + ( 4 x (+/- the expander frequency)) etc, etc, etc. Unless good filtering is used you'll be able to tune quite a few of those....and no expander I've ever seen has a decent filter. Hence the reception of 83.7MHz at 93.7MHz (and 73.7MHz and 103.7Mhz and 63.7MHz and 113.7MHz if you could tune them all). The higher order products will be lower in level but they are still there. All of these frequencies will be radiated back out the antenna as there are no filters to stop them. From this you have a 10MHz expander which is not needed for an Australian band receiver. This is also one reason why the higher frequency expanders are better (18MHz and 20MHZ) as most of the unwanted frequency products are shifted out of the FM (broadcast) band.....not so good for low flying aircraft that are near you though as these unwanted products that are higher in frequency will end up in the VHF aircraft band!! It's not a good thing when the poor pilot who is trying to get directions to land his plane can only hear JJJ.
The short answer is "NO" you don't need an expander for a new head unit that tunes the Aust. FM band.
Stephen Howlett TryHard victoria soarer/ 1992/tt auto & 1996 V8
Saturday, December 31, 2005 - 10:50 am, by: Stephen Howlett(Solar)
hey mark, i was trying to tune my radio fitted with a expander yesterday for a particular station (vega fm) which is 91.5 australian fm i cant get it , why ??
Saturday, December 31, 2005 - 09:14 pm, by: Mark Paddick(Sparks)
Soarer radio tunes from 76 to 90MHz; only 14MHz wide which is one reason they are hard to convert as our band is 20MHz wide. If you have a 18 or 20MHz expander the 91.5 will end up at 71.5MHz or 73.5MHz which is outside the tuned band so you won't receive it. A 10MHz expander will put it at 81.5MHz which you will tune. I suspect that this is your problem. With a 10 MHz expander you will tune some stations twice through the band though. For example the common 88MHz frequency will tune at 88MHz and 78MHz, not a huge problem. What will happen though is that some lower power stations will not be received well if at all due to losses in the expansion process.
Friday, July 10, 2009 - 08:49 pm, by: Brett Harrison(Bretto)
To bring this old relic of a topic up again. Is there any consensus on the best Fm expander to use, from the above I should go for an 18MHz. Does anyone recommend a particular brand ? and how about the switchable expanders. I was just going to head to Jaycar and grab one, but will probably end up with some junk.
Saturday, July 11, 2009 - 05:08 pm, by: Brett Harrison(Bretto)
Yeah, Ive tried three different ones, last one I got was a switchable one from Jaycar, believe it is from NZ. Its pretty good, however need another one for a different car. Just seeing if there have been any new ones on the market worth getting.