EMRFD Message Archive 8088
Message Date From Subject 8088 2013-01-12 14:47:38 James H attenuator to use with clock oscillator? 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,
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 <email@example.com>
> 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.
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,
C/San Roque, 4-1º
web del club: http://www.eaqrp.com
Tel.: +034 96 120 17 67
Movil: 651 35 35 11
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