Subject: Old working wide band catv tuner. Date: Mon, 13 Nov 2000 19:43:35 -0800 From: "Rein A. Smit"
Newsgroups: rec.radio.amateur.homebrew Hello All, I am looking for a 50 - 800 Mhz catv tuner that can be tuned and ramped with a dc voltage. Perhaps someone can tell me the reason why I can't find this stuff on the net ( Is it the 900 MHz Fed policy? ) 73 Rein W6/PZ0ZN Subject: Re: Old working wide band catv tuner. Date: Mon, 13 Nov 2000 20:57:32 -0800 From: John Miles Organization: MDI Newsgroups: rec.radio.amateur.homebrew Rein A. Smit wrote: > > Hello All, > > I am looking for a 50 - 800 Mhz catv tuner that can be tuned and ramped > with a dc voltage. > Perhaps someone can tell me the reason why I can't find this stuff on the net > ( Is it the 900 MHz Fed policy? ) > > 73 Rein W6/PZ0ZN Do you really need a tuned front end? If not, you can think of http://www.minicircuits.com as your own personal tuner-construction menu. They sell inexpensive VCOs, mixers, filters, and MMIC amplifiers that can be used to construct just about any broadband 50-ohm RF system with no more difficulty than hooking up a kitchen sink. -- jm and catv tuner. Date: Mon, 13 Nov 2000 21:23:08 -0800 From: "Rein A. Smit" Organization: MindSpring Enterprises Newsgroups: rec.radio.amateur.homebrew Hi John, Thanks for response. Lots of interesting stuff on you WEB site! I like to build a spectrum analyzer around one of those tuners.. Sort of faced with a 50-60 Mhz. IF so I one needs some form of preselection I think. Will look into the minicirciuits approach, Never thought about that, quite frankly. I can't understand why I can't find surplus tuners on the WEB. There must be plenty around and I am also confused how those LO.s are driven in VCR's, I guess it must be digitally, at least in the newer ones. Rein Subject: Re: Old working wide band catv tuner. Date: Tue, 14 Nov 2000 01:24:51 -0500 From: Michael Black Newsgroups: rec.radio.amateur.homebrew On Mon, 13 Nov 2000, Rein A. Smit wrote: > > Hi John, > > Thanks for response. Lots of interesting stuff on you WEB site! > > I like to build a spectrum analyzer around one of those tuners.. Sort of > faced with a 50-60 Mhz IF so I one needs preselection I think. > > Will look into the minicirciuits approach, Never thought about that, > quite frankly. > > I can't understand why I can't find surplus tuners on the WEB. There > must be plenty around and I am also confused how those LO.s are driven > in VCR's, I guess it must be digitally, at least in the newer ones. > > Rein > I'm certain they are all voltage controlled. Though some might be a better choice than others for your purpose, because greater integration might make it more difficult to use the tuner as a non-stepped device. It should be very easy to find such tuners, and if your first find isn't suitable, another one should come along soon. Places to look are tv sets, something recent enough that it isn't the old turret type. TV sets have gone through some iteration since the turret tuners were dropped, so some sets may provide a more useable tuner. There was a time when TV sets were made where you'd have a fixed number of channels, but little ports behind a panel to tune those channels to your local selection. Then there are the sets where you could tune all the channels, but they are all digitally tuned. I can't think right now, but I'm sure there were some other schemes in between that all used voltage tuned tuners. Keep an eye out on garbage day, and just strip out the tuner. TV repair places are often a good source o9f junked tv sets, and you might even ask them directly if they had any junkers. External cable converters should also be a source. I see these at garage sales in plentiful quantities, selling for about five dollars or so. VCRs have such tuners too. You may be able to find or buy for a minimal amount a VCR that is mechanically broken, but the tuner works fine. In the tv sets, the tuners tend to cover segments, and need switching as you move up in frequency (though the tuning within the segments will be voltage controlled). So the VHF channels will be broken down into 2 or three segments, plus another one for UHF. All the cable converters I've looked at tune in one band. I don't know how consistent this is, but from an article in Radio Electronics about building such a "spectrum analyzer", they showed a block diagram of a cable converter, and it tuned everything up to a fixed IF, and then in another mixer down to channel 3 or 4. I imagine a scheme like this is used in some tv sets. VCRs probably use different schemes. Some of the earlier ones had those little tuning knobs behind a panel, and I thought they required that you set a tiny switch to VHF-lo, VHF-hi or UHF. But lat4er ones probably act work like the cable converters. Often, the tuner modules in all three instances are distinct modules, and have the pins marked on the metal case, though the markings may be a little cryptic. A little guessing, a little experimenting, and you should be able to figure out the pinouts. The frequency coverage probably varies depending on whether the unit covers just the traditional over the air channels, or the cable channels too, since the latter puts channels into non-tv frequencies. Something that covers channels 2 to 13 probably won't go all the way up to 800 MHz, though perhaps the tuner would have some extra coverage on both sides. UHF would be covered by a separate tuner. SOmething that covers the cable channels would have wider tuning range, though I don't know the exact range. I remember in one article about using cable tuners for a "spectrum analuyzer" that some tuners may be a better choice than others, but I think it was because some ran off a negative voltage. Tuners that work with some digital scheme will have a prescaler on the VCO (though sometimes, the prescaler is separate), though often they have a high division rate. But it provides a means of measuring the VCO frequency; tuners that were merely voltage controlled may not have the prescaler, or any VCO output so you'd have to add that if you needed access to the VCO output. It should be really easy to find something to get started, and if it doesn't work fully or not at all, a little more patience should turn up something locally for a few dollars. Michael VE2BVW Subject: Re: Old working wide band catv tuner. Date: Thu, 16 Nov 2000 03:24:47 -0800 From: "Rein A. Smit" Newsgroups: rec.radio.amateur.homebrew Hello Michael and Others, You provided quite some useful info. It is clear now to me now, that they ( the tuners ) all use VCO's and that some are driven directly with a DC voltage and that others are driven by the voltage from a comparator/freq synthesizer, the new designs that use remotes etc My question is how difficult is is to separate that driving module from the actual vco voltage drive point. Another qustion I have is what is the freq range of these VCR tuners if they say 181 chaneels. From 50 to approx 800 MHz? I found a web page with a nice clean design, but I do not like to draw attention to it. If you contact me direct I will send you the URL The reason? Well I am sure by now, that this tuner business is a hot issue as it relates to the scanner laws in a way. And that is the reason that so many links have gone dead. 73 Rein Actually I've never run across a general-purpose commercial spectrum analyzer that uses a preselected front end at HF/VHF/UHF frequencies. The usual practice is a dual- or triple- (or even quadruple-) conversion technique, first upconverting the RF region of interest to a very high first IF. That way, a single fixed filter can be used to reduce image response (probably doing a better job than the front ends of the cheap CATV tuners). For example, you could choose a POS-2120W ($21.95) to sweep from 1 to 2 GHz, driving something like an ADE-5 mixer ($3.45, hard to believe not a misprint). The IF would be around 1 GHz, with RF response from HF all the way to 1 GHz. Then follow the mixer with a bandpass filter of some sort. Maybe a BLP-1000, followed by a MMIC buffer, followed by a PHP-1000; total cost about $30. You could probably omit the highpass (PHP) part if you wanted, with some additional risk of spurious signals coming through the whole chain. Better yet, buy one of the nice commercial-grade cavity filters that (for example) firstname.lastname@example.org is always selling on eBay. The cell phone industry seems to dump nice UHF bandpass filters on the surplus market like they're going out of style or something. The choices are endless, because your image response is going to be many hundreds of MHz away from the desired sideband, and it won't take much filtering to get rid of it. Once you have your 1 GHz first IF signal, you can mix it with a 950 MHz signal to get your desired 50-60 MHz final IF. Again, images should be no problem as long as you have even a crude lowpass filter that cuts off somewhere between 50 MHz and 2 GHz after the 2nd mixer. You can get the ~950 MHz 2nd LO from another POS-2120W -- it would probably be quite stable with a simple fixed bias network, maybe a thermistor for temperature compensation, or a simple fixed-modulus PLL if you feel more ambitious. Most of the homebrew spectrum analyzer schemes out there just use a 10-turn pot or something similar to tune the CATV tuner's LO, so using another VCO with a fixed voltage divider as your 2nd LO wouldn't be a terrible thing to do. If you want digital tuning, you'll have to drive the first LO with a PLL of some sort, or at least a high-precision DAC. An obvious solution would be to multiply the output of a DDS VFO by 256 or so. A 74HCT4046 from Radio Shack could do the job, with a frequency divider made up of some of the Motorola ECLips chips. I wouldn't try this at first -- it's a fair bit more work, and it wouldn't make sense unless you phase-locked the 2nd LO as well to keep it from drifting. Just tune the VCO with a precision potentiometer, and you have a workable DC-1 GHz receiver front end for less than $100. With all the cheap 50-ohm system components out there, it's all just plumbing. One VERY nifty advantage to a 1.0 GHz 1st IF would be to use a cheap 2 GHz handheld counter to monitor your 1st LO with a piece of black tape over the first '1' digit. Voila -- your receiver or spectrum analyzer now has a direct-reading digital frequency display. Also, be sure to have a look at Wes Hayward's analyzer project page (http://www.teleport.com/~w7zoi/SA.html) for further ideas and construction hints. -- jm http://www.qsl.net/ke5fx Subject: Re: Wideband RF homebrewing (was Re: Old working wide band catv tuner.) Date: Thu, 16 Nov 2000 03:47:44 -0800 From: "Rein A. Smit" Newsgroups: rec.radio.amateur.homebrew Hello John, Again thanks. I have not had the time to look up the minicircuits catalog. The approach is certainly attractive. But at this point I like to go the tuner route. There is a lot of tuner specs. info available from Asian sources and what they publisch is not too bad as far as image and NF data are concerned. My intention is just to have a device that I can use it to tune LO's perhaps filters, in short as a simple tool to help with a number of vhf / uhf projects that I have planned to do. Your modular approach is certainly something I will look for if I ever make it up to 10Ghz. 73 Rein Subject: Re: Old working wide band catv tuner. Date: Thu, 16 Nov 2000 01:21:51 GMT From: email@example.com Organization: Deja.com - Before you buy. Newsgroups: rec.radio.amateur.homebrew In article <3A10B4E7.BD48DD66@ix.netcom.com>, "Rein A. Smit" wrote: > > > Hello All, > > I am looking for a 50 - 800 Mhz catv tuner that can be tuned and ramped > with a dc voltage. > Perhaps someone can tell me the reason why I can't find this stuff on the net > ( Is it the 900 MHz Fed policy? ) > > 73 Rein W6/PZ0ZN > There a number of "generic" CATV tuners avilabe from commercial outlets like MCM Electonics and Parts Express. I am currently working on a RCVR based one I bought for that purpose it has a 70 Mhz IF using a xtal filter fron a cell phone, the reciever is a TDA 7000 IC and LM 380 audio amp. Tuning is with a 100K 10 turn pot. dr.d Sent via Deja.com http://www.deja.com/ Subject: Re: Old working wide band catv tuner. Date: Thu, 16 Nov 2000 03:34:31 -0800 From: "Rein A. Smit" Newsgroups: rec.radio.amateur.homebrew Hi Dr D, Tnx for message and info. Yes, I had seen that page earlier and had a little problem watching it as it in Postscript. But I got it printed! As said in a previous message, I think we should not draw attention to it because whoever has it up there, may violate some Fed. law. The reason I write this is that after long searches with search engines I have gotten convinced that there is something going on about these tuners and their docs. TOO many dead and not available web pages. Regards Rein