Kenwood double DIN and now a cheap 7" double DIN, both have crap reception, like 6 stations will autoprogram only 40 miles from Los Angeles! . The stock non-Nak stereo kicked *** and pulled probably 30 stations until it went silent. Do these have power amplified antennas? I know they extended to the frequency of the FM but does any other part of the antenna system need 12V for an amplifier? I was reading a few posts outside the Lexus community about this subject and quite a few found they did not hook up their 'antenna amplifiers' when they put in their aftermarket head units. Once they found this wire, their reception improved 1000%. I used the "SC400 aftermarket head installation" thread and it works great but the FM an AM reception just sucks with the stock antenna connection.

 

The stock setup uses the diversity antenna, which incorporates the power antenna and rear window grid. It's not amplified. Look up the info for the y-cable to adapt both, although it's not clear if that actually pulls in both signals or if the stock HU has a switching capability.

 

Yes the stock FM antenna is amplified. A trigger wire from the radio runs to the motorized antenna and also triggers a relay that amplifies the FM signal at the same time. There is an additional wire that connects to the headunit that tells the antenna to extend or retract a certain amount depending on what station on the FM range you are trying to listen to (as far as I know, no one has got this function to work with aftermarket radios). The AM antenna is in the rear window glass. I do not believe it is amplified. On the stock headunit, the FM and AM antennas are different antenna wires that plug into the back of the headunit next to eachother. If I remember right they are slightly different gauge wires and different sized plugs. The primary antenna is standard [import] size and the secondary antenna is GM size.

*Ok a little update (2/18/24) on this. I am currently swapping out the radio in my IS300 and it has the same 2 antenna setup.
The big antenna which I mislabeled above as the FM antenna is actually the primary antenna (AM & FM).
The smaller gauge antenna in the rear window glass is the secondary antenna (AM & FM).
The stock radios ARE diversity antennas meaning they use both antennas at the same time to pull in weak stations and will switch from 1 to the other for the clearest signal. In a diversity setup, the primary antenna is amplified and the secondary is not. That is on purpose so that the factory radio can pull in the strongest signal without interference.

 

^ Looks like your memory is better than mine.

https://www.clublexus.com/forums/lex...orking-32.html

"There are two power antenna wires and two antenna connections (FM and AM). The stock radio flips one of the power antennas for FM and the other for AM. You'll most likely use FM with your aftermarket headunit so you'll use only the top power antenna wire in your harness."

Although, my faulty memory may have been influenced by contradictory info.

https://www.clublexus.com/forums/sc-...nna-fix-2.html

"Yes, the OEM head units are supposed to be able to dynamically switch between the rear window glass antenna and the mast antenna in order to use whichever gives the strongest signal for a given radio station."

A quick search didn't turn up anything regarding your assertion of there being an amplified signal and relay.

 

Here is the wiring diagram for the primary antenna. This is from a 97 but the wiring should be all the same (*except maybe for some colors)

AMP is a trigger wire. This gets a power signal when the head unit turns on. The stock head unit uses this wire to turn on the factory amp, the subwoofer amp, and the antenna all at once.

B is constant +12V via the 20A Radio #1 fuse

ACC is power when the car is in the ACC mode thru the 7.5A Radio #2 fuse

E is factory ground. You can't see it in this diagram but it is a dedicated ground wire just for the antenna.

IG is power when the car is ON thru the 15A ECU-IG fuse

Now there are 3 antenna "power" wires. I do not know which does which.
ANT
ANTA
ANTB

And lastly, there is the standard gauge banana plug for the power antenna wire. The smaller glass antenna wire you can leave unplugged, since aftermarket radios now don't use a diversity system. *(see my next post)

And worth noting, the factory antenna mast also has a braided steel wire on it. This wire connects the antenna shaft to the metal antenna assembly bracket that is bolted to the vertical metal trunk support that is aft of the wheelwell. The antenna assembly that seats up against the rear quarter panel has sharp "teeth" on it that bite into the rear quarter metal when tightened (if you have ever removed the antenna nut or replaced an antenna you will see this. And to make a better ground, the antenna assembly bracket is bolted to the vertical metal trunk support with a serrated nut. The bolt part is fixed to the bracket.

 

Now there is a trick you can do to use both factory antennas.
Buy a standard [import] antenna Y cable (1 male, 2 female ends). And buy a "GM antenna adapter" which will convert the smaller banana plug to the standard size.

Metra 40-GM12
Scosche MDAB

This mod is very popular in the Toyota truck and SUV world because those guys like to take the masts of their fender antennas but keep the amplified base there, because running the glass antenna by itself isn't strong enough to pick up radio anywhere.
The amplified base up front and the glass antenna out back gives near OEM clarity and reception.
And a few guys swear running the complete front antenna + the rear is better than factory, with some claims of pulling in clear stations 60 miles away (I assume this has to do with overlanding)