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Wideband FM @70MHz? - RF Cafe Forums

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Mike_From_Plano
Post subject: Wideband FM @70MHz? Posted: Tue Apr 21, 2009 5:13 pm

Captain

Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14
Hello,

I've been workng on a fiber optic video link and I chose to try 70MHz FM. This used to be fairly easy using components from Signetics; they had a 70MHz IF chip with a built in qud detector and a 150 MHz PLL.

Well, I'm feeling a bit like Rip Van Winkle, I look around and there are all of these phase modulation parts and PLLs that are up in the GHz, but I'm not finding anything quite like I was used to. I'm also on a tight power budget (battery powered...), so I don't think anything the digital folks offer would be of any help.

Anybody have any suggestion for an OLD analog engineer?

Best Regards,

Mike


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yendori
Post subject: Re: Wideband FM @70MHz?Posted: Wed Apr 22, 2009 2:28 pm

General


Joined: Thu Sep 25, 2003 1:19 am
Posts: 50
Location: texarcana
Hi Mike,

This is Rod from Plano.

Here are some links you may or may not have already checked.

http://www.freescale.com/
http://www.nxp.com/
http://www.intersil.com/cda/home/
http://www.analog.com/en/index.html
http://www.ti.com/
http://www.national.com/analog
http://www.linxtechnologies.com/
http://sanyo.com/

http://www.digikey.com/
http://www.mouser.com/

Good Luck,

Rod


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biff44
Post subject: Re: Wideband FM @70MHz?Posted: Wed Apr 22, 2009 8:56 pm

Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 33
Good luck! I am in a similar situation. I am doing a non-coherent coding gain experiment with fsk receivers, and needed a simple 915 MHz receiver chip with an ANALOG fm demod out. I searched around for hours. Nada. Everything nowadays is too complex, data slicers, no access to the analog output, no access to the ADC outputs, etc. I did finally find a small quantity of old RFM chips on ebay, and am all set. You might find the chip style you are looking for on ebay, especially where the HAMs are selling stuff.

You could probably find a chip if you are willing to go down to either 10.7 or 13 MHz. A lot of wireless keyboards and mice were designed at 13 MHz, so the reciever chips are probably still available. They just recently moved up to bluetooth frequencies.

You could probably find a receiver with some sort of zero IF with an fsk demod output.

Good luck
Rich

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com

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Mike_From_Plano
Post subject: Re: Wideband FM @70MHz?Posted: Thu Apr 23, 2009 1:04 am

Captain

Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14
Thanks guys,

I appreciate your support. It seems we're caught up in the knowledge of the ancients. I'm contemplating going old-school on this thing - complete with messy cans.

Hmmm, I wonder how good the ol' SA602 would be as a quad detector? It has the bandwidth. Then, I need a good IF, complete with limiting.

Anybody have any suggestions for the IF / limiter? I'd hate to go bone knives and bear skins on it...

Mike


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biff44
Post subject: Re: Wideband FM @70MHz?Posted: Thu Apr 23, 2009 4:52 pm

Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 33
As long as you are not endeavoring to construct a mnemonic memory, you should do fine.

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com

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biff44
Post subject: Re: Wideband FM @70MHz?Posted: Fri Apr 24, 2009 11:59 am

Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 33
seen on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0193331528

not sure if that price is for 1 or 10 pcs.

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com

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Mike_From_Plano
Post subject: Re: Wideband FM @70MHz?Posted: Fri Apr 24, 2009 4:10 pm

Captain

Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14
Hey Rich,

Pretty sweet chip, but I gotta move these things into production. I spoke with a fellow at Analog Devices and he suggested the AD603 as an IF. It's good for 90MHz, has an AGC, and high output drive. I think I'll give it a shot with an attenuator (to reduce reflection), and a pair of schottky's for limiting.

That still leaves me looking for a modulator / demodulator that can give me the bandwidth at 70 MHz. I'm tempted, on the demodulator, to run a 1/4 wave delay off of the limiter and beat it against the original. I don't know what it would do for my S/N, since the signal would be small, but it'd sure be simple.

PLLs make my head hurt. Fast PLLs make it hurt worse....








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