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Old 19th October 2012, 05:32 AM   #21
BrianL is offline BrianL  United States
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The first part of his series -- the MPLX decoder is at:
http://www.kilmory.demon.co.uk/jlh/JLH_1.jpg
http://www.kilmory.demon.co.uk/jlh/JLH_2.jpg
http://www.kilmory.demon.co.uk/jlh/JLH_3.jpg
http://www.kilmory.demon.co.uk/jlh/JLH_4.jpg

I have not been able to locate the remainder of the articles.
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Old 19th October 2012, 12:54 PM   #22
rsavas is offline rsavas  Canada
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Thanks for the information, see if we can find the front end & IF schematics.
To test for transmitter distortion, you can get a HP 8901A modulation analyzer. I bought one on eBay. We used these back in the day at Motorola for 2-way radio testing. The 8901A was a very expensive piece of gear back in the day, now you can get them for around $100, which is a steal. Shipping costs are higher than the unit cost. If you do buy one, try to get one with the built-in calibrators & a 10MHz reference oven. As a SG, I purchased a HP 8656B. It does not have stereo modulation capabilities, but that can be an external device connect to the ext. modulation input. There are a few designs on the net for a stereo modulator.

Regards
Rick
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Old 20th October 2012, 08:06 AM   #23
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Rick, I checked on ebay and it seems you are right about the low prices of that HP gear. I'll be monitoring them for sale in the UK because the postage from US does cost as much as the item itself.

The front end is a ready built ALPS unit from Japan I think, and is used as is, unmodified. From this, the output goes into a small IF amp board consisting 3 transistors and 4 ceramic filters. This then goes into the CA3189 board with the JLH VCO arrangement, then into the JLH sample and hold stereo decoder. I had searched the web, and could not find the published schematic for the IF and VCO parts.

David.
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Old 20th October 2012, 01:55 PM   #24
rsavas is offline rsavas  Canada
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Alps, front end, well that explain the sensitivity issue. So it is a varactor FE and how is the tuned freq displayed? I have an old ETI article from JLH as well, probably pre-dates your updated version. Same sort of setup, used a CA3089 if I recall, oh ya, learnt how to wind that quad coil. I can asist you in designing a new, more sensitive front end. I have a whole folder on this stuff.Need equipment however, I guess that i why I never got the job done. Out of date however, you will never get to the performance & features of a Si4735. This part cost <10$, it is fantastic technology. I'd say my Si4735 sensitivity, channel selection, is equiv to the tuner in my Pioneer SX-950. The Si4770 will probably better the tuner in the SX-1250, all for a couple bucks. It makes no sense to me to hold onto the old technology, it is nostelga/history. I place my complete stereo besides a spare SX-950 tuner unit, I scratch my head saying wow, this is where we have come in 30 years. Don't want to discourage you, but want to make sure you are aware of todays technology. I would appreciate, for someone to help me write code for my tuner/stereo

Rick

Last edited by rsavas; 20th October 2012 at 02:12 PM.
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Old 20th October 2012, 02:09 PM   #25
rsavas is offline rsavas  Canada
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Default Test Equipment

I bought a HP 8656B for spare parts. I had it shipped from Israel to Canada. I think I paid $100US and it cost about the same to courier it. I have a near complete spare parts bin. I bought the 8656B unit locally, paid around $300 I think, AM mod was not working, it was a unit from Motorola, it was a unit that I cal'd back in the 80's, can you believe. Fixed the AM problem, dead 10-bit DAC, MC3410L . I got some free service manuals, 2 binders, since they were throwing them away, they had so many of them, most tech benches needed one to test the 2-way radios that were being mfgd. Service manuals are free at Agilent BTW. Great units, gotta know what your doing to fix them however. I wonder if there is a forum for fixing old HP stuff :-) That's it for now.
Take care
Rick
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Old 22nd October 2012, 12:46 AM   #26
BrianL is offline BrianL  United States
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Given the ready-built front end in the JLH tuner, one could consider using a 'vintage' tuner and gutting everything after the front end. For example, the Dynaco FM-5 has a decent tuner with good front end and can be had on eBay for <$100. Just replace the IF onward.

It will be interesting to see the entire JLH schematic. One thing I'm cautious about with British tuners is that they often don't fare well in the crowded US broadcast spectrum due to poor adjacent/alternate-channel selectivity -- something that is apparently not as big a problem in the UK (or at least wasn't for years).
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Old 24th October 2012, 10:33 AM   #27
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I was thinking along similar lines, but say, taking a NAD4020 and taking out the quad coil, and replacing it with the VCO by JLH. I just might try this to see how it affects the sound/performance. I'm guessing that the harmonic distortion is not the definitive improvement, but rather another type, perhaps IM, phase distortion or some other artifact.

I also have some Arcam tuners from just after this period, which also use the CA3189 but using the LM4500 as decoder, and these may also be a good target for the JLH VCO too.
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Old 24th October 2012, 01:20 PM   #28
rsavas is offline rsavas  Canada
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CA3189/LM4500, brings back memories, I still have some of these parts.
Considering that in Europe, the channel spacing is 100KHz, deviation is 50KHz,one would think that the filters need to be somewhat sharper and less BW than what is required in North America, that and the 50us deemphasis.
Cheers
Rick
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Old 24th October 2012, 02:35 PM   #29
DF96 is offline DF96  England
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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.
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Old 24th October 2012, 02:59 PM   #30
rsavas is offline rsavas  Canada
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I guess that I will have to make some measurements on my tuner to confirm your statements.
Rick
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