On Thu, 29 Jan 2009 22:40:29 -0500, Garey Barrell wrote: >I don't recall just how much LO is available, but I'm pretty sure a >Mini-Circuits SRA-1H or SRA-3H would work just fine in that spot. The >CM1 is long gone....
Found it. This page discusses replacing a CM-1HF with a SRA-3MH: http://www.sm6rpz.se/radio/mod7.php Also this, from KE9OA: <quote> Both of the units are ok out of the box, but I have improved the performance of both of my units by replacing the Vari-L CM-1 1st mixer with a Mini-Circuits SRA-3MH. This is a Level 13 mixer that has only 4.77dB of midband conversion loss vs the 6.5dB conversion loss that the CM-1 has. The CM-1 is rated down to 500kHz (or is it 1MHz?) while the SRA-3MH is rated down to 40kHz. Drake got around this problem by interchanging the RF and I.F. ports, since the I.F. port on this mixer is rated down to DC. Still, the replacement mixer has lower conversion loss, so you can improve the noise figure of the unit by 1.73dB. and that is without having to use an RF stage ahead of the mixer. The result is better performance, since any RF amplification ahead of the mixer would degrade its IP3 performance by the amount of gain that this RF stage is providing. As an example, if your IP3 is +20dBm, if you place 10dB of amplification ahead of the mixer your IP3 will degrade to +10dBm. Another improvement that I did with my units was to replace the 1N4148 diodes that Drake uses in the 2nd mixer with a matched quad set of 1N5711 hot carrier diodes. This will improve the IMD performance of this stage After all of these mods, the MDS improves from 0.15uV to 0.07uV. Not bad for a few hours work! </quote> The above note is excerpted from a post at: http://groups.google.com/group/rec.radio.shortwave/msg/619c60c0a90e02c7 As a side note, I've done the hot-carrier (Schottkey) diode mod to the 2nd mixer and translator (as suggested by SM6RPZ), and it works. I'm really curious about the SRA-3MH mod. I notice that the SRA3-MH has been replaced by SRA3-MH+. I'm not sure what the differences are, other than RoHS compliance. 73 -Jim -- Ham Radio NU0C TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://radiojim.exofire.net http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
