Tuners: analogue, synthesized and beyond

[Karl vd Berg]

Great!

After seeing all this, I just wonder how the hell an iPod tuner section function!

An externally hosted image should be here but it was not working when we last tested it.

 

[DF96]

If FM it will (probably) be using SDR techniques. Sound quality will be compromised anyway by the poor antenna which will cause multipath problems in many locations.

 

[Karl vd Berg]

What are the most important parameters one should take in consideration in choosing a Tuner?

Channel separation? THD? S/N ratio? Number of gangs? All of them together I guess. So what would be the 5 or 10 best ever tuners?

 

[DF96]

It depends partly on your location. In a big city with lots of FM stations you want good IF selectivity and low intermodulation in the VHF front-end. If you live far away in the countryside then good sensitivity is more important. Number of tuning gangs is a weak measure of what matters: 2 are not enough, 3 or 4 are fine if done properly, 5 suggests specmanship.

Distortion (mainly 3rd order if the IF and discriminator are correctly aligned) should be low - 0.1-0.5% are typical. S/N ratio can be 70dB or better, but the real issue is how much signal is needed to achieve this.

I haven't taken much notice of commercial tuners. My first was a kit. Second was my own design, loosely based on Hitachi datasheets.

 

[Karl vd Berg]

It depends partly on your location. In a big city with lots of FM stations you want good IF selectivity and low intermodulation in the VHF front-end. If you live far away in the countryside then good sensitivity is more important. Number of tuning gangs is a weak measure of what matters: 2 are not enough, 3 or 4 are fine if done properly, 5 suggests specmanship.

Distortion (mainly 3rd order if the IF and discriminator are correctly aligned) should be low - 0.1-0.5% are typical. S/N ratio can be 70dB or better, but the real issue is how much signal is needed to achieve this.

I haven't taken much notice of commercial tuners. My first was a kit. Second was my own design, loosely based on Hitachi datasheets.

Very, very interesting...

I live in the city, but Amsterdam area has an easy tuning selectivity, no need of narrowing IF band, I guess. But, to be honest, I'm using kind of 2,5m of coaxial antenna to the tuner (I live in the highest floor). So if I put it to a proper antenna then maybe the tuner will get more signal and stays quieter with less background hisses?

 

[DF96]

Perhaps. You should not need a big antenna for FM reception in a city, unless all the transmitters are somewhere else.

 

[Richard Ellis]

I am kind of curious, what kind of antenna DO you have at the end of your two & a half meters worth of coax??
There is the simple Dipole which commonly came in the box of the tuner when new, it was an opaque white flat wire, T shaped.....which connected directly to the back of the tuner, at the 300 Ohm terminals.
The coax either had a screw in terminal, or one had to convert the 300 to 75...thru your cable & reconvert back to 300 at the antenna.
I found several DIY sites that build their own antennas...I found one that makes a DIY # Collinear Array# ..This particular antenna puts out a pattern similar to a flattened doughnut shape..........perfect for your application as no power is wasted coming in from straight up. Dirt cheap to build & really cool stuff.

___________________________________________________Rick..........

 

[Karl vd Berg]

I am kind of curious, what kind of antenna DO you have at the end of your two & a half meters worth of coax??
There is the simple Dipole which commonly came in the box of the tuner when new, it was an opaque white flat wire, T shaped.....which connected directly to the back of the tuner, at the 300 Ohm terminals.
The coax either had a screw in terminal, or one had to convert the 300 to 75...thru your cable & reconvert back to 300 at the antenna.
_________Rick..........

I tried something weird today, Richard.

I arranged a 300 ohm T-shaped "connected" to the coaxial one, making it simply an extension. Then, I put the 300 ohm part in an "L" (90 degrees) shape on the top corner of the ceiling leaving the rest of that cable coming down the wall like a "Y" shape. It's working slightly better than before, specially on the 94.30 MHz Classic Radio, which has usually an annoying "hiss" of background. For the other station it improved a lot.

As DF96 mentioned above, maybe this is the limit of receiving signal to my tuners. Since the stations are not far from the city and I live in the highest floor, only a "super tuner" (7-gangs or super aligned) could do better?

 

[AuroraB]

An easy check if weak signal is the cuplrit, is if the tuner has a true mono switch. You need appx 20 dB more signal in stereo, to achieve an approximate same S/N ratio as in mono, given the way the FM stereo signal is designed.

 

[Richard Ellis]

I tried something weird today, Richard.

I arranged a 300 ohm T-shaped "connected" to the coaxial one, making it simply an extension. Then, I put the 300 ohm part in an "L" (90 degrees) shape on the top corner of the ceiling leaving the rest of that cable coming down the wall like a "Y" shape. It's working slightly better than before, specially on the 94.30 MHz Classic Radio, which has usually an annoying "hiss" of background. For the other station it improved a lot.

As DF96 mentioned above, maybe this is the limit of receiving signal to my tuners. Since the stations are not far from the city and I live in the highest floor, only a "super tuner" (7-gangs or super aligned) could do better?

So, did you install the two impedance matching transformers when you arranged your antenna? one transformer out the back of the tuner, to the 300 ohm terminals, screwed into the 75 ohm cable, then another one at the far end, connection to the antenna???
If you didnt you have a big impedance mis-match, & it is not getting much signal power.

____________________________________________Rick.........