1236	2007-12-16 16:44:28	Robert Cerreto	MiniCircuits POS Series VCO
Message	Date	From	Subject
I am building a General Coverage receiver to be used as a test bed for the lab. I would like to use a PLL controlled 1st oscillator in the front end. The VCO for this oscillator will need to be a wide range VCO. My question is: "Is a Mini Circuits POS series VCO suitable for this purpose? The receiver will tune from approx. 1.8Mhz to 50 Mhz. The first I-F will be about 8Mhz. Are the noise specs for the POS series good enough? 73 es TNKS, Bob WA!FXT --------------------------------- Looking for last minute shopping deals? Find them fast with Yahoo! Search. [Non-text portions of this message have been removed]
1237	2007-12-16 17:48:13	Allison Parent	Re: MiniCircuits POS Series VCO

1238	2007-12-16 21:41:09	Baruch Zilbershat...	Re: MiniCircuits POS Series VCO
--- In emrfd@yahoogroups.com, "Allis
1239	2007-12-17 04:35:15	w4zcb77	Re: MiniCircuits POS Series VCO

1240	2007-12-17 15:03:26	Ed Almos	Re: MiniCircuits POS Series VCO
There is a big problem with using a single VCO module to cover a 30 MHz span for a receiver. Have a look at the math: 16v span (average for a POS module) gives 30 MHz change 30/16 = 1.875 MHz per volt divide both sides by 1000, 1.875 KHz per mV As you can see, a change of one millivolt will shift your received signal by nearly 2 KHz, this means no noise of any kind can be allowed
1247	2007-12-19 14:56:06	Wes Hayward	Re: MiniCircuits POS Series VCO
Hi Bob, Harold, and group. Bob, you can probably use a POS VCO as a first experiment with a PLL LO for your receiver. You may want to refine that later, but I'm sure you will learn a lot with the first experiments. I agree with Harold: A DDS synthesizer is probably a better solution. We have all heard, and probably experienced the wisdom that DDS has lower wideband phase noise than a PLL synthesizer. But the DDS still has to be designed with care. I did an experiment the other day that applies directly to this situation. A few years ago a friend had sent me a DDS synthesizer that he had built. It used old technology by today's standard, but it was OK at the time. It used an AD9850, which we know uses only a 10 bit DAC in the output. The part is not specified to have low spurs. It is still regarded to produce low wideband phase noise. But this is not what I found just last week when I turned the circuit on for some other experimental needs. The phase noise was terrible
1250	2007-12-20 17:28:06	Robert Cerreto	Re: MiniCircuits POS Series VCO
Wes, Ed, Harold, Allison and group, Thank you all for your replies. And, thank you for spotting a a slight typing error. Yes, the first I-F will be about 108Mhz, not 8Mhz. This would give me the tuning range I needed with the POS in my junkbox. All advice is duly noted and will be used. I fibbed a little though. The "test bed" receiver is also a learning process for me. This was one of the goals. So, I have decided I would get the receiver up and running with the front end mixers etc. ,I-F, and audio stages using a simpler narrow band LO scheme. Then, in the interest of my education I will play with PLL's and DDS stuff for the LO. After all, that is why the "test bed" is being built....to experiment and learn about stuff that I haven't played with. As you can see, I am very passionate about this stuff but, naive. I have read the theory on the PLL's ( wideband noise etc.) and DDS's and just have to breadboard the theory to actually see it work and just plain futz with it. When the futzing is complete, I hope to have a high quality piece of gear and will share my adventures (and questions) with all who want to listen. So, thanks for the help from all of youse. And, I extend my warmest wishes to you and your families for a happy Holiday season. 73, Bob WA!FXT Wes Hayward <wesw7zoi@gmail.com> wrote: Hi Bob, Harold, and group. Bob, you can probably use a POS VCO as a first experiment with a PLL LO for your receiver. You may want to refine that later, but I'm sure you will learn a lot with the first experiments. I agree with Harold: A DDS synthesizer is probably a better solution. We have all heard, and probably experienced the wisdom that DDS has lower wideband phase noise than a PLL synthesizer. But the DDS still has to be designed with care. I did an experiment the other day that applies directly to this situation. A few years ago a friend had sent me a DDS synthesizer that he had built. It used old technology by today's standard, but it was OK at the time. It used an AD9850, which we know uses only a 10 bit DAC in the output. The part is not specified to have low spurs. It is still regarded to produce low wideband phase noise. But this is not what I found just last week when I turned the circuit on for some other experimental needs. The phase noise was terrible
1251	2007-12-21 01:27:50	Jason Milldrum	Re: MiniCircuits POS Series VCO
Bob, I'm looking forward to seeing what you find out in your experimentation. I feel that PLL theory is one of the weaker aspects of my RF knowledge, so I'm always looking for insight into the design and (especially) the troubleshooting of the beasts. I have to deal with microwave PLLs on a regular basis at work, and I find the subtleties to be a bit challenging. Good luck! 73, Jason Milldrum, NT7S ===== Amateur Station NT7S - <http://www.nt7s.com> QRPedia - <http://www.qrpedia.com> On Dec 20, 2007 5:28 PM, Robert Cerreto <wa1fxt@yahoo.com> wrote: > I hope to have a high quality piece of gear and will share my adventures > (and questions) with all who want to listen. > > So, thanks for the help from all of youse. And, I extend my warmest wishes > to you and your families for a happy Holiday season. > > 73, Bob WA!FXT