209	2006-11-26 13:32:59	Robert Cerreto	Need Some Toroid Advice
Message	Date	From	Subject
I need a 20uh coil for a 2Mhz VFO. The oscillator I chose is a standard series tuned colpitts. I choose the series tuned colpitts to minmize effects of external capcitances/inductances etc. on the tuned circuit. I only have room for a toroid in the box. I tried using a FT37-61 core and found it to be very unstable. I am winding about 30 - 35 turns on two stacked T-50-6 cores. The cores had to be stacked to give me more inductance. I am hoping that stacking cores would not change temperature characteristics. If I use a parallel tuned colpitts, I could use a smaller value of inductance. But, I want this VFO to be rock solid and impervious to meachanical "bumps".So, the tuned circuit can't be affected stray capacitance/inductance....thus the high L to C ratio of the series tuned circuit seems best. Does anyone have any comments or advice on the above? Thanks guys....BTW this is a great list isn't it????!!!!!! 73 es 72, Bob WA!FXT Check out the all-new Yahoo! Mail beta - Fire up a more powerful email and get things done faster.
210	2006-11-26 14:04:10	Loren Moline WA7S...	Re: Need Some Toroid Advice
Bob, My VFO for my 40 Meter direct conversion receiver has lots of capacitance. It is very stable. Actually believe it or not it has 2 inductors in parallel. One is a 10.7Mhz IF transformer and another is a slug tuned coil to get the freq up because with all the capacitance the freq was too low with the IF transformer. Loren ----Original Message Follows----
211	2006-11-26 14:20:31	Bill Noyce	Re: Need Some Toroid Advice
You can get 20 uH with about 45 turns on a T50-1 (blue) core. It has AsubL of 100 (uH/100turns^2). My recollection is that this mix has the best Q for use in the 1.5-2.0 MHz range, though the quoted temperature stability isn't as good as the -6 or -7 mix. The T50-1 is available at partsandkits.com as well as other toroid sellers. I've recently been rereading the section in IRFD that shows the progression from Colpitts to Clapp to Seiler oscillators, and how each one alters the needed inductance. If I'm remembering correctly, the Clapp is your series-tuned Colpitts; the Seiler adds another capacitor in parallel with the inductor, allowing the inductor to be smaller. Might be worth reviewing that theory... -- Bill, AB1AV On 11/26/06, Robert Cerreto <wa1fxt@yahoo.com> wrote: I need a 20uh coil for a 2Mhz VFO. The oscillator I chose is a standard series tuned colpitts. I choose the series tuned colpitts to minmize effects of external capcitances/inductances etc. on the tuned circuit. I only have room for a toroid in the box. I tried using a FT37-61 core and found it to be very unstable. I am winding about 30 - 35 turns on two stacked T-50-6 cores. The cores had to be stacked to give me more inductance. I am hoping that stacking cores would not change temperature characteristics. If I use a parallel tuned colpitts, I could use a smaller value of inductance. But, I want this VFO to be rock solid and impervious to meachanical "bumps".So, the tuned circuit can't be affected stray capacitance/inductance....thus the high L to C ratio of the series tuned circuit seems best. Does anyone have any comments or advice on the above? Thanks guys....BTW this is a great list isn't it????!!!!!! 73 es 72, Bob WA!FXT Check out the all-new Yahoo! Mail beta - Fire up a more powerful email and get things done faster.
212	2006-11-26 14:24:24	ks1u	Re: Need Some Toroid Advice
Robert: You may get some differences of opinion here, but here's mine. Sometimes you have to accept a compromise between size and stability with vfos. The most stable vfo I ever built was a Vackar and it was a heterodyne using a 4 MHz xtal and a vfo operating at 3 to 3.15 MHz. It sounds like this is not a heterodyne, and as such there is likely to be some drift even if it is not detectable by anything other than a frequency counter. Every vfo I built using toroids drifted a bit, some more than others. You might try the slug tuned inductors made by Amidon, such as the L-57-6. My experience has been it drifts less than a toroid, is adjustable, small in size and enables you to use small gauge wire to get reasonably high inductance values. The slug tuned inductor should not take up any more space than a couple of staked T50-6 units with wire. You'll have to check the inductance per turn values, but it would be better to use the number 6 material than number 2. Another possibility is to use a small ceramic or plastic core and wind number 30 wire on it until you get the right inductance. 73 George
213	2006-11-26 15:06:41	Alan Jones	Re: Need Some Toroid Advice
Loren, What design did you use to build your 40 meter direct conversion receiver? I want to build a 40 meter receiver and I am looking at different designs. How do you like your receiver's performance? How much band spread do you have? Alan Loren Moline WA7SKT wrote: > > > Bob, > > My VFO for my 40 Meter direct conversion receiver has lots of capacitance. > It is very stable. Actually believe it or not it has 2 inductors in > parallel. One is a 10.7Mhz IF transformer and another is a slug tuned coil > to get the freq up because with all the capacitance the freq was too low > with the IF transformer. > > Loren
214	2006-11-26 16:08:48	Loren Moline WA7S...	Re: Need Some Toroid Advice
Alan, Mixer and VFO are from Solid State Design For The Radio Amateur although Im sure there are good ones in EMRFD. Mixer is a MC1496 which in my opinion has less microphonics than some NE602 and SA612 mixers. I use a 365 variable for tuning and set the series capacitor to give me the proper bandspread. Receiver consists of 1 transistor and 2 IC's with the audio amp being a LM386. I have heard DX from around the world with it on CW and sideband. It does not drift enough to detect and my VFO would work great for a QRP transceiver.I have a single tuned front end and have no problems with BCB interference except of course the stations actually
215	2006-11-26 16:26:12	Loren Moline WA7S...	Re: Need Some Toroid Advice
Robert, I have never used a toroid coil for a VFO and have never ever even considered it. There are many places to use a toroid but in my opinion a slug tuned coil is a better choice loaded up with lots of capacitance like at least 470pf from base to emitter and emitter to ground on a 2N3904 type. I used poly capacitors in mine as opposed to dipped micas. Loren ----Original Message Follows----
219	2006-11-28 09:06:30	topossibilities	Re: Need Some Toroid Advice
Bob I have had great success in building very stable oscillators using a type 6 toroid core (TC of +35 ppm/deg-C) and a combination of NPO (i.e. COG) and polystyrene capacitors (TC of -150 ppm/degree C). By making 1/3 of the total tank capacitance with polystyrene capacitors, from start up, the oscillators had a brief (less than 5 minutes) and small frequency change (less than 100Hz). Thereafter, it stabilized to no more than +/- 5Hz. Notes: These were Hartley circuits (simple and low parts count) with the feedback tap made at 17% and used air variable type trimer and tuning capacitors. Ed, W1AAZ PS Another trick to TCing an oscillator is to determine if a + or - coefficient capacitor is needed. Then if you have a capacitor of the approximiate value and TC, install it in series with a variable capacitor (e.g. such that total series C and TC are somewhat near the required range). Now you can fine tune the required compensation. Lots of parts, books, test equipment and kits for sale at: http://mysite.verizon.net/topossibilities/index.html Adding more as time permits....if you don't see what you want, check back or ask.
220	2006-11-28 09:28:18	Joe Rocci	Re: Need Some Toroid Advice
Bob, Great experience-based practical design advice. Thanks! What frequency-range were the oscillators for which you cited the drift numbers? Joe W3JDR ----- Original Message -----
222	2006-11-29 15:04:24	topossibilities	Re: Need Some Toroid Advice
Joe, The oscillators were for a 5MHz LO used in a 20/75M SSB transceiver with a 9.0Mhz IF....however, I have also built oscillators operating at much higher frequencies with simuliar results. Another technique I have used when building a LO at a much higher frequency was to process the signal through a 'Johnson walking ring counter'. Johnson counters divide by 4 and provide very accurate I/Q (90 degress out of phase) square waves outputs for driving diode ring mixers. Note that any drift is also divided by 4. When using 74HCTxxoutput D flip flops and a 100 ohm pull up, the level is 7dBm into a 50 ohm load. The applicati
223	2006-11-30 06:06:33	w4zcb77	Re: Need Some Toroid Advice

224	2006-11-30 10:18:25	Robert Cerreto	Re: Need Some Toroid Advice
First of all, I d like to say Thank-you to all the guys on this wonderful list for all your constructive advice. It helped. Heres what we finally did. We couldnt use the series colpitts configuration like we wanted, because the junk box didnt have the correct cores to get the inductance required. So, we went back to a parallel colpitts. It oscillated right off, but, drifted upwards without ever stopping. Realizing that this was more than just than just a temperature compensati
225	2006-11-30 15:05:28	Bill Noyce	Re: Need Some Toroid Advice
Congratulations, Robert -- that's impressive! Some comments on your list: > Lessons learned: > > Use the minimum voltage possible for VCC. -- This minimizes power dissipation in the oscillator, so it minimizes heating and the resulting drift. Unfortunately, it means there's a lower signal-to-noise ratio into the transistor, and therefore increases the oscillator's phase noise. No free lunch, I guess. > > Load the resonator as little as possible -- How small a coupling capacitance did you end up with for your 2 MHz oscillator? > > Not all NPO's are NPO's and NPO's are not "driftless". > > Capacitor markings don't always tell the truth. -- Bill, AB1AV