[Milsurplus] LO radiation
J. Forster
jfor at quik.com
Mon Mar 28 22:38:02 EST 2005
I have one and a manual copy, but not to hand. As I remember it was the RA 6217, but it's
only a vague memory. The clever part was the locking (somehow) of the up and down conversions
to a 1 MHz comb...but to different comb spikes. That canceled out drifts in the up and down
conversion. I'm SURE it was patented, so you might get some help in that direction.
I'm posting this to another list that has some Racal fans on it. They may know more.
-John
mstangelo at comcast.net wrote:
> John,
>
> Would you know the model of that RACAL receiver that used the 30-70Mhz IF?
> I'm trying to find the first military and commerical HF receivers that used upconversion.
>
> 73,
>
> Mike N2MS
>
> > The first such design I am aware of
> > is a roughly 1965 Racal design where the RF is mixed with a LO somewhere in the
> > 30 to 70 MHz range, and later down converted again. This design has problems
> > even with today's high intercept mixers and Racal and Harris receivers often
> > require pre selectors.
> >
> > If you rule out the direct up-conversion sets, the input stage of a receiver
> > would have a tuned circuit of fairly high Q before the mixer, even if there is
> > no TRF stage. Thus, I'm inclined to think that the LO would be isolated from the
> > antenna by 20 dB or more.
> >
> > [snip]
> >
> > > Again it's not a calculation of what *does* happen, it's only a
> > > calculation of what *could* happen. Without real data on real radios
> > > (and antennas - good point) you are never going to get real world data.
> >
> > It's also unlikely any receiver is going to achieve the noise floor of a
> > shielded dummy load in actual service.
> >
> > > If you were going to look at real data I think it you should look both
> > > at the LO and at harmonics of the LO. The combination of antenna gain
> > > and match might be better on the second or third harmonic ....
> >
> > I'm not so sure the harmonics will get past the input selective stage in WW II
> > gear.-John
> ______________________________________________________________
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