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RE: [linrad] RE: Hardware
- Subject: RE: [linrad] RE: Hardware
- Date: Fri, 10 Jan 2003 02:46:08 -0000
Hi Conrad, Josh, and others,
It is looking more and more like I will be going single conversion.
Where we will probably part ways is in the local oscillator.
I am fond of using available circuits, so I will probably use a 25Mhz
PLL robbed from a CB and mix it with a temperature compensated
crystal oscillator multiplied then mixed with the PLL output to produce the
needed LO. Since I like to rob Motorola Micors, I will also be using
helical filters robbed from them to produce needed selectivity in the
144 Mhz RF path.
The place we can probably go down the same path is in the actual
2m to 2.5 Mhz mixer and later, the 2.5 Mhz LNA.
Josh, if you really want to go with the Time Machine, you can use
an off the shelf 144 to 28 Mhz converter. Then get the 28 Mhz Time Machine.
After studing it for myself, I concluded that I would not be happy, after the
first time the Time Machine produced garbage, when I am just about to copy
an EME dxpedition from a rare Country. Of course my need is for two channels,
making the RX2500 a lot more attractive for me in terms of price.
If you are talking about going to a standard sound card, then you have
the additional need for providing many frequency steps for frequency coverage.
PLLs add phase noise. Crystals, although low in phase noise, are expensive.
Then you must also provide IF selectivity. The RX2500 and Delta 44 start looking
very attractive, very quickly once you fully understand the lesser options.
Of course if you like to experiment and the cost of replacing an obsolete black box
does not bother you, then, you could certainly learn a lot doing the experiment.
If you are going from 144 Mhz direct to a sound card, then you need an exceptionally
low phase noise LO and and exceptionally good mixer, so phase noise from the LO
does not show up as FM and AM noise.
I would suggest to you that the demands on dynamic range are very stiff
for Linrad. It would be real easy to build something that works poorly.
You can do it yourself, but arm yourself with information first. Read and study
Leifs and the W3SZ web site on Linrad. After reading about the RX2500 and
why it is the way it is, I decided;
1) I could not duplicate it for myself and
2) I need it.
If you can imagine a ham neighbor only
a few miles away keying a clean carrier INSIDE your SSB passband and then
trying to copy a weak CW signal inside the same SSB passband at the same time, then you
get a very general idea of what is needed for a 96 KHZ passband receiver.....
Then think of the Time Machine as similar to using a low end CB in a Large active city.
Your mileage may vary.
On 9 Jan 2003 at 19:21, Conrad G0RUZ wrote:
> In a word yes! I expect that Jim UWA and I will be going down a
> similar route, perhaps between us we could get something up on a
> OK, I don't have a 2.5 MHz input so I need a different frequency, I
> was working on going straight to sound card. But I would like to know
> where you find information on building something like this.
> I like the idea of low cost and easy, but truly it is hard for me
> (with out any building experience) to look at some of the ideas
> suggested on yours and w3sz site to know how to build anything.
> Rogers two stage design looks trivial, but then I wonder how it all
> fits together. I think I have an OK idea on some of the pieces.
> Others are still a mystery. And when I once started to make a parts
> list two resistors did not have values, and the capacitors did not all
> have units. Some people can probably just know how these were
> supposed to be used, but for me this is too much of a jump to make.
> The TimeMachine looks to be an OK start for HF, but something is still
> needed to go from 2M to HF. Maybe this is a good starting point for
> my next idea, but only if we have a plan to get higher.
> Is there soneone on this list that knows enough to lead a hardware
> building session. Something that is simple and cheap, but with enough
> steps and notes and pictures that everyone can work on at the same
> time and maybe learn how some of this works. Ideally this can then be
> archived in a way that anyone can come later and follow the same
> process and learn the same things that we just did.
> Is there any interest by others in a process like this?
> Later, JOSH (kd7hgl)
73, Jim Shaffer, WB9UWA.