[Milsurplus] LO radiation

[mstangelo at comcast.net]

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