EMRFD Message Archive 10393
Message Date From Subject 10393 2014-10-31 06:45:48 Jim Miller SA602 Max recommended oscillator input? I'm going to drive my little SA602 upconverter with an external 10Mhz oscillator. What is the maximum recommended level for this? It isn't listed on the datasheet that I can find.I have 10dbm readily available.Thanksjim ab3cv 10394 2014-10-31 06:51:15 Tayloe, Dan (NSN ... Re: SA602 Max recommended oscillator input?
I believe that 300 mV of drive is the recommended level.
- Dan, N7VE
10395 2014-10-31 06:57:08 Jim Miller Re: SA602 Max recommended oscillator input? DanThanks!jim ab3cvOn Fri, Oct 31, 2014 at 9:50 AM, 'Tayloe, Dan (NSN - US/Arlingt 10396 2014-10-31 13:55:19 pa_lender Re: SA602 Max recommended oscillator input? 2v PP Hi Jim
From p. 81 of Doug DeMaw's 1991 QRP Notebook, referring to the NE602 (should be identical) : "Make certain that the VFBO injection voltage to pin 6 of U1 does not exceed 3 volts P.P. Excessive injection power can cause strong harmonic currents to develop within the NE602 detector. This gives rise to all manner of spurious signal responses in the receiver tuning range. Too little injection power, on the other hand, reduces the conversion gain of the chip."
He recommended 2 volts pk-to-pk -- I don't know what dBm this is, since I don't know the impedance at the injection point, which is certainly higher than 50 ohms -- 200?
He was talking about his "Universal Direct Conversion Receiver."
Good luck, and 73s...
-- Paul, AD0HQ
10397 2014-10-31 14:09:05 Dana Myers Re: SA602 Max recommended oscillator input? 2v PP 10398 2014-10-31 14:52:57 pa_lender Re: SA602 Max recommended oscillator input? 2v PP I agree that it seems too high, but, truly, the text says 3V max and the schematic (on p. 78) says "2V P-P." Maybe it's an editor's misunderstanding, but I think if DeMaw meant something under one volt he'd have said "mV."
I'm curious myself and can test this shortly in a simple project. I was working recently to boost the output of an AD9850 into that range and finally succeeded with EMRFD Fig. 2.57. I'll post any meaningful results.
-- Paul AD0HQ
10399 2014-10-31 14:56:34 Dana Myers Re: SA602 Max recommended oscillator input? 2v PP 10400 2014-10-31 14:57:39 Dana Myers Re: SA602 Max recommended oscillator input? 2v PP 10401 2014-11-01 10:27:25 kb1gmx Re: SA602 Max recommended oscillator input? That is excessive by a factor of 10 easily.None of the datasheets nor any vendor literature has that as a valid voltage.By actual measurement using 8568B spectrum analyser at 2V PP thespurs are horriffic. Backing off to about 300mV PP into 50 ohms at theosc input (just about 0dBm) produced a much cleaner output withspurious mix products more than 30db down. This is a very low powerdevice with a fair amount of gain. The signal then at the RF input mustbe less than -12dbm or the IMD will be severe and lower by a few dBwould be cleaner.Reminder the osc input and RF inputs of this mixer have roughly about16db of gain. I'd use 2V PP applied to something like a SBL1H(level 21 mixer) DBM.Allison/KB1GMX 10402 2014-11-01 10:41:43 kb1gmx Re: SA602 Max recommended oscillator input? The DDS bare produces almost as much as needed maybe more.A single transistor amp would have no problem developing well abovethe needed signal. Even then I'd include a pot to optimize the correct voltage.I'd look at comentery in EMRFD as there was much discussion in chapter5.3and it includes the recommended numbers for its use.I'd go with 0dBm or slightly less but more than 200mV PP for the LO. There islatitude on this and its also variable with Pin-8 voltages (8V max). With Vcc at 8Vyour can use 0dBm and 5V (very commonly done) that drops to under that by asmuch as 6dB but that varied from unit to unit and depends on if you want agood IMD (low spurs) or maximum conversion gain.Allison 10403 2014-11-01 12:03:42 pa_lender Re: SA602 Max recommended oscillator input? Thank you Allison for the authoritative answers and citation. I'm new to the group. This is very encouraging.
-- Paul AD0HQ
10404 2014-11-01 14:48:22 kb1gmx Re: SA602 Max recommended oscillator input? One comment GET THE BOOK. ;)EMRFD is a wealth of information and loaded with technique.Allison 10405 2014-11-01 16:29:46 pa_lender Re: SA602 Max recommended oscillator input? Got the book, just hadn't looked very hard. The Gilbert Cell discussion from section 5.3 (pp. 5.10-5.12, again thank you Allison) is very comprehensive. The authors got the best IMD results at 0 dBm (632mV pk-to-pk) with a 51-ohm resistor (through 0.1uF bypass) at Pin 6. Conversion gain of 18dB.
-- Paul AD0HQ