Homebrew Receivers

[w3sz <w3sz@xxxxxxxxxxxxxxx]

Hello all,

Just a quick note to those who might be contemplating 'rolling their
own' front ends to use with LinRad.  The April RadCom Technical Topics 
by Pat Hawker G3VA features a variation by I7SWX on the H-mode mixer by 
G3SBI.  With these mixers IIP3's in excess of +40 dBm (up to +55 dBm!!) 
are reported.

These are, like the mixers Leif shows on his webpages, switching mixers. 
 What the differences are between the H-mode mixers and Leif's design 
(if any) I am not smart enough to see, except that the transformer 
configuration appears different with the H-mixers.

These H-mode mixers mixers are also shown in the new ARRL Experimental 
Methods in RF Design book on pages 5.15 and 5.16, and used in a 
practical receiver on 6.48 and 6.49.  This reference describes this 
H-mode mixer design as 'perhaps the most exciting work published in the 
past decade in this area'.

On the web they are discussed by PA3CKR at www.qsl.net/pa3ckr/himixer/

The CDG2000 uses them www.warc.org.uk/cdg2000/introduction.htm
		Slightly off this topic, you might also have a look at the LO phase 
noise specs on that page for the CDG2000.

There is an amusing rant on another list that complains that the writer 
was able to achieve an IP3 of 'only +40 dBm' with the H-mode mixer.  How 
sad ;)

I'd appreciate any comments to the list by those who can comment on 
whether they have had experiences with these mixers, and to compare and 
contrast them with the switching mixers on Leif's pages.

One interesting note is that PA3CKR built one version that used the 
Minicircuits T4-1 rather than a roll-your-own transformer and the 
FST3125, and that gave a respectible +41 dBm IIP3 (Input IP3).

Thanks in advance,

Roger Rehr
W3SZ

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Roger Rehr
W3SZ
2 Merrymount Road
Reading, PA 19609
http://www.qsl.net/w3sz




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