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Old 24th October 2012, 03:34 PM   #31
DF96 is offline DF96  England
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Measuring your tuner will tell you nothing about my statements.
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Old 24th October 2012, 04:02 PM   #32
rsavas is offline rsavas  Canada
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FM deviation in Europe is 75kHz. Although 'channels' may appear on any multiple of 100kHz the frequency planning means that local signals are unlikely to appear within less than about 400kHz (and usually much more - the original BBC stations were spaced 2.2MHz apart). The usual recommendation for Europe is 180kHz IF bandwidth for mono and around 280kHz for stereo.

I think our 50us deemphasis gives slightly higher noise and slightly lower distortion than 75us.
In North America, or at least in the Toronto, Canada area, the FM band is near full capacity, I receive signals at regular 200KHz spacings. I even receive signals on the same frequency in certain atmospheric conditions. This becomes a problem for some stations, expecially if you have a omni-directional antenna. I receive signal from both the US and Canada. I am using a large fringe Yagi mounted on a 40ft tower with a amplifier on the top of the mast.
Not sure why you think that I can not use the HP8656B SG to test the Si4735 tuner for S/N,THD using 50 or 75 KHz deviations, with deemphasis setting of either 50 or 75uS? Can you explain why?
Rick
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Old 24th October 2012, 04:54 PM   #33
DF96 is offline DF96  England
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Sorry, I misunderstood. Yes you could check the effect of changing deemphasis. The noise change should occur for all signal levels, but the distortion change may only be seen at higher modulations because preamphasis affects HF headroom.
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Old 25th October 2012, 04:18 AM   #34
BFNY is offline BFNY  United States
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Quote:
Originally Posted by rsavas View Post
In North America, or at least in the Toronto, Canada area, the FM band is near full capacity, I receive signals at regular 200KHz spacings. I even receive signals on the same frequency in certain atmospheric conditions. This becomes a problem for some stations, expecially if you have a omni-directional antenna. I receive signal from both the US and Canada. I am using a large fringe Yagi mounted on a 40ft tower with a amplifier on the top of the mast.
Not sure why you think that I can not use the HP8656B SG to test the Si4735 tuner for S/N,THD using 50 or 75 KHz deviations, with deemphasis setting of either 50 or 75uS? Can you explain why?
Rick
First, comments on channel spacing. You likely know that most government authorities, like the FCC in the US, assign FM channels based on typical receivers, like those in cars. If you have a super duty tower mounted FM Yagi (or log periodic) long boom antenna rig, of course you can receive more distant stations than a typical car. And you will have problems with adjacent and co-channel stations. Channel assignments in the US usually allow for 400kHz spacing. This spacing allows the US HD digital FM system, which intrudes into adjacent channels, to work OK. But it's a pain for the guys with great tuners and antennas trying to DX.

On to test gear. The HP 8656B is a nice low phase noise signal generator, but not that great for modern stereo FM tuner testing. The bandwidth on the FM modulation is not enough for phase linear stereo composite signals, limiting the separation. In this case, you need flat phase response to 53KHz.

And the HP 8656B FM modulation circuit is not super linear, meaning you can't generate low distortion test signals. I have not looked at the spec recently, but if it is 0.5% or 0.3% THD, that's probably right. The best dedicated FM stereo generators with FET linearized FM modulation circuits can easily go to 0.03% or lower THD, 0.01% is typical in the best units.

I own 4 of the better FM stereo generators, including the Sound Technology ST-1020A, Panasonic VP8122A, Meguro MSG-2161, and RE 104 driven by an HP 8904A with options for FM Composite output. All of these get to way better than 50dB FM stereo separation, and way better than 0.03% distortion at 100% modulation.

Last comment - the Silicon Labs chips are for car radios. They are a single chip solution, but nowhere even close to the best vintage FM tuners for reception options, stereo separation, distortion, and dynamic range.

Look closely at the specs, and compare to, say Yamaha TX-1000, Denon TU-800, Kenwood KT-990, etc. And with simple ceramic filter mods, selectivity is easily modified using hand matched and sorted 180, 150, or 110 kHz Murata ceramic filters. These fairly simple selectivity filter mods can turn these tuners into unmatched FM DX machines.

For sound quality, mostly all of our FMTuners members agree that certain tube tuners, like those from Sherwood, Scott, Fisher, can best the solid state models provided you have a good antenna and signal. Sorry to get into this a bit long, but been doing this for a good while, and wanted to share some extended thoughts.
Bob
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Old 25th October 2012, 02:10 PM   #35
rsavas is offline rsavas  Canada
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Default FM Tuners

Hi Bob,

Nice to see you following this thread. Good information and explanations for all of us.
I have not done any measurements on the Si4735 radio thus far. Actually no reason to, other that out of interest. I have however done a comparison to the Pioneer SX-950 tuner. The Pioneer tuner is probably one of the better ones, for the day, although a SX-1250 tuner would be one step better.
By scanning the dial, I see that the adjacent ch selectivity in the Si4735 is not as good as the Pioneer, sensitivity wise, it is on par. Variable stereo blend, sliding LP filtering, selectable IF bandwidth are all excellent features, near impossible to do in the analog domain. Maybe one of those Magnum Dynalab ones maybe better.
I will however try out the newer Si4770 part this winter and see what improvement that they have made, stay tuned, for that. The sensitivity on paper for the Si4770 part is remarakble. Want to check out the selectivity however. Hard to beat a $5 piece of silicon.
Car radio FM tuners seem to be driving the market, they do have some obsticles to contend with such as muti-path, something that a DSP based tuner, would excel at and an anlaog tuner would probably suffer.
After using the Si4735, well I can put the Pioneer to bed and no need to find a SX-1250 or anything else, once I get the Si4770 going.
Yes the ole HP8656B was never designed for ultra low distortion FM modulation. I liked this model since it was dear to my heart in the Motorola days. I used to cal/fix these things.
I have a HP8901A as well & have made the THD measurement on the 8656B. Even if I use the Amber DA set as a external modulation source, it will never go below 0.1%, which ain't bad for what I am doing. Of course I wish I had better gear but I am doing it as a hobby and not professionally.

Cheers
Rick
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Old 25th October 2012, 03:28 PM   #36
BFNY is offline BFNY  United States
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Quote:
Originally Posted by rsavas View Post
I have not done any measurements on the Si4735 radio thus far. Actually no reason to, other that out of interest. I have however done a comparison to the Pioneer SX-950 tuner. The Pioneer tuner is probably one of the better ones, for the day, although a SX-1250 tuner would be one step better.
By scanning the dial, I see that the adjacent ch selectivity in the Si4735 is not as good as the Pioneer, sensitivity wise, it is on par. Variable stereo blend, sliding LP filtering, selectable IF bandwidth are all excellent features, near impossible to do in the analog domain. Maybe one of those Magnum Dynalab ones maybe better.
Hi Rick, I am impressed you've got the Si4735 working, it's a decent project.

I have a portable here that uses the same series chip, the Tecsun PL-606, which sells for about $49. USD. It allows for using an external 75 ohm antenna, and has a stereo output. So I hooked to my roof mounted 9 element FM antenna, and compared it to some of my better tuners. It did well, especially for selectivity. But was not as good as my best FM tuners for sensitivity, and sound quality. For a portable, though, the Tecsun PL-606 is a great little portable FM radio, especially for its size, and I use it a lot.

The Pioneer units you reference above are receivers, which usually were not as good as the top line dedicated Pioneer tuners, i.e. TX-9500II or TX-9800 from the same time frame. The TX-9500II/TX-9800 both have selectable width IF filters (wide and narrow) and so do many other top FM tuners. Some, like the better Yamaha tuners (but there are many others) have 3 or more IF bandwidths, stereo blend, and so on.

You can read the reviews of the best ones here at our website -
Tuner Information Center - Vintage Stereo Tuners
The prices for many of the best FM Tuners are very reasonable used, especially when you consider what they sold for new.

And sadly, very few companies make really good FM tuners equivalent to the best ones from 10-30 years ago. The few units that are available sell for absurdly high prices, starting well over $1,000.00 USD. Since you can buy some of the best ones used for under $200., most people go that way if they want the best performance and sound quality.
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Old 25th October 2012, 04:03 PM   #37
rsavas is offline rsavas  Canada
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Default FM tuners

Hi Bob,


Working on the Si4735 was a fun learning experience for me. See attached pictures of the portable tuner/media player.
I wonder what the Si4735 would sound like with an external DAC (I2S output)? I guess that I will only find out if I give it a go, yet another project :-) . This is what I was planning for my tuner/pre-amp project, but it got a bit much, so I scaled it down a fair bit to get my programming experience level up to snuff.

Regards
Rick
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Last edited by rsavas; 25th October 2012 at 04:06 PM.
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Old 30th October 2012, 11:50 AM   #38
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My God ETI what a magazine!!!!!
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Old 27th July 2013, 09:19 PM   #39
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Hi guys,

although this thread is already a bit outdated, I have a question regarding the pre-emphasis / de-emphasis thing.
To my knowledge this comes from the early (FM-)days when nobody spent any thought about stereo.
Then is was a good idea to emphasise the higher frequencies before they get transmitted and to deemphasise them after demodulation.
In stereo-transmissions we get the (higher) noise from the difference-channel mixed in anyway and it influences the highest as well as the lowest frequencies in the same way.
Thus I belive that emphasis/deemphasis is just important for compatibility but not for noise-reduction in stereo-transmissions.
Therefore I would not expect a big difference between 75s or 50s deemphasis at all (as long as there are no overmodulation or limitation-effects).
May be I am wrong?
Let me know how you think.

HH

Last edited by HolgerHa; 27th July 2013 at 09:23 PM.
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Old 27th July 2013, 09:32 PM   #40
DF96 is offline DF96  England
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De-emphasis still reduces noise for stereo, because it reduces HF gain. The fact that much of the noise has a different source and a different spectrum does not change this.
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