8088	2013-01-12 14:47:38	James H	attenuator to use with clock oscillator?
Message	Date	From	Subject
Hello All, I am planning on constructing a HF to VHF upconverter to use with the DVB sticks. I plan on using a 100 Mhz clock oscillator that runs on 3.3 volts, feeding its output into a NE602 mixer. The VHF output starting at 100 MHZ would then be feed into the receiver module. I need to know if the output from the clock would be too much to input into the NE602. If so, then can someone provide information as to a good attenuater that would work in such a circuit? Thanks anf 73, James, AA5AO Abilene, TX
8092	2013-01-12 16:26:24	Thomas S. Knutsen	Re: attenuator to use with clock oscillator?
This is actualy fairly trivial to figure out, so lets do some math: If we assume the oscillator have 3V P-P voltage out, this equals 13.5dBm in 50 ohms, but unfortunatly the output impedance of the oscillators vary all over the place, so check the datasheet of the part you are going to use. For an regular DBM, an 6dB attenuator would match this to an acceptable level, but make sure you follow that with an lowpass filter. The attenuator would ensure that you always have an good match to 50 ohm for the filter. If you are going to use the NE602, I have seen them used with LO from -30dBm to 0dBm, so I would put an 10dB attenuator after the filter as well, it keeps an good returnloss for the filter. The NE602 is an lousy mixer for use on HF with an IIP3 of -13dBm. The DVB stick I got have an decent IIP3, so you would benefit from using an regular diode ring mixer, and they can easily be homemade. Also, some filtering in the input is mandatory to avoid strong out of band signals. An bandpass filter for each band may be a bit tedious to make, but it gives an much better preforming system than just connecting the mixer directly to your antenna. 73 de Thomas LA3PNA. 2013/1/12 James H <jameshickox@sbcglobal.net> > ** > > > Hello All, > > I am planning on constructing a HF to VHF upconverter to use with the DVB > sticks. I plan on using a 100 Mhz clock oscillator that runs on 3.3 volts, > feeding its output into a NE602 mixer. The VHF output starting at 100 MHZ > would then be feed into the receiver module. > > I need to know if the output from the clock would be too much to input > into the NE602. If so, then can someone provide information as to a good > attenuater that would work in such a circuit? > Thanks anf 73, > > James, AA5AO > Abilene, TX > > > -- Please avoid sending me Word or PowerPoint attachments. See <http://www.gnu.org/philosophy/no-word-attachments.html> PDF is an better alternative and there are always LaTeX! [Non-text portions of this message have been removed]
8093	2013-01-12 19:21:26	kb1gmx	Re: attenuator to use with clock oscillator?

8094	2013-01-12 21:28:37	Jerry Haigwood	Re: attenuator to use with clock oscillator?
James, The spec sheet for the NE602 only says the minimum input clock is 200mv (I am guessing p-p voltage). The SA612 says the lock input voltage should be between 200-300mv. So to stay on the safe side, I would use something like 250mv. A standard resistor divider should work to lower the 3V or so output down to 250mv. Jerry W5JH - located in deep East Texas! "building something without experimenting is just solder practice"
8097	2013-01-13 05:16:32	Bob	Re: attenuator to use with clock oscillator?
Hi All - I'd like to refer you to post 2642 for an example of interfacing a 5 volt clock oscillator to a 50 ohm system. While this post deals mostly with 8307 based power meters and a calibrator for use with them, it also details that 50 ohm interface. I think the ideas therein could be scaled for the 3.3 volt oscillator depending
8098	2013-01-13 06:01:04	victor	Re: attenuator to use with clock oscillator?
Contrary to the other responses, a square wave LO into the 602 will improve both the noise figure and the intercept point (linearity). The amplitide at the 602 LO input should be at the 100-200mV p-p. A higher level sine signal acts exactly the same, switching the mixing section of the 602 as an ideal dpdt switch. So in principle if the square signal duty cycle is close to 50% then a LPF is not needed. Victor - 4Z4ME
8099	2013-01-13 07:05:47	Bob	Re: attenuator to use with clock oscillator?
Hi All - I agree with 4Z4ME - based on my own experiments, sq wave drive to the 602 LO port is generally FB and can have lower p-p amplitude than a sine wave for similar operation. Somehow in my thinking Iinadvertently mixed sq. drive to the RF and LO ports (I have done both). Note that while the RF input MAY often be derived from a 50 ohm system, drive to the LO port can easily be more "sloppy". Thus, I think LO drive derived from a clock oscillator need not stick to a 50 ohm source impedance. As a guess, a few hundred ohms should be FB though I can't say I actually did this myself. (I would not hesitate to try this.) A higher LO source impedance makes the attenuator be more like a simple divider affording a lighter load
8100	2013-01-13 07:45:04	Juanjo Pastor	Re: attenuator to use with clock oscillator?
I agree with Thomas, a diode mixer would be better. And better using frontend preselectors, as local FM stations and other VHF signals on the ether could wreak havoc... 73, 72 de Juanjo, EC5ACA. EA-QRP #104, G-QRP #9742, QRP-L #1662, FP #899. Juanjo Pastor C/San Roque, 4-1º 46460 Silla SPAIN e-mail: ec5aca@gmail.com web: http://www.geocities.ws/ea5chq web del club: http://www.eaqrp.com Tel.: +034 96 120 17 67 Movil: 651 35 35 11 ----- Original Message -----