1399	2008-02-04 13:17:01	Markus Hansen	Re: Digest Number 471
Message	Date	From	Subject
As a further note to Diode Ring Mixers, recently I had an interesting experience using a TUF-1 in my homebrew 10 band transceiver. I replaced an older transmitter chain that didn't have any output at 6 meters with the G6ALU MOSFET amplifier chain. It works like a charm but decided I should check the output with my SA on all 10 bands and when I noticed a close in spur on 80 meters, 400 khz below the carrier at only -36 db below the carrier level. After a few moments with the calculator I determined that it was a the result of the VFO 4th harmonic beating with the Xtal injection osc. in the HFO module. I checked the response of the 3 section S-series BPF that follows the HFO module and it looked just like it was supposed to with over 80 dB rejection at the VFO 4th harmonic. Emmmmmm. I then began checking osc. levels into the HFO TUF-1 mixer. The xtal osc. power injection power measured +7 dBm and the VFO injection power -10 dBm. Should be OK according to Wes's recommendation in EMRFD. However when I decreased the level of the VFO power to -12 dBm, the offending spur disappeared off the SA screen, ie. more than 80 db below the output carrier. I checked my Power meter calibration against my HP8640 so see if the power meter was giving a correct indication of measured power and it was OK dead on, ie. HP8640 set to -10dBm measured -1dBm on the Power meter at the VFO freq. Not satisfied, I exchanged the TUF-1 for another one which I had in my parts bin in case the the TUF-1 mixer was faulty. Same result. Conclusion: Be mindful of injection levels when using a double balanced mixer especially for a transmitter and check the output with a SA before using it on the air. Markus VE7CA
1403	2008-02-04 14:25:21	Markus Hansen	Re: Digest Number 471
Whoops, I made an error. My Power meter read -10 dBm when the HP8640 output was set at -10 dBm. On Feb 4, 2008 11:26 AM, Markus Hansen <mkve7ca@gmail.com> wrote: > As a further note to Diode Ring Mixers, recently I had an interesting > experience using a TUF-1 in my homebrew 10 band transceiver. I replaced an > older transmitter chain that didn't have any output at 6 meters with the > G6ALU MOSFET amplifier chain. It works like a charm but decided I should > check the output with my SA on all 10 bands and when I noticed a close in > spur on 80 meters, 400 khz below the carrier at only -36 db below the > carrier level. After a few moments with the calculator I determined that it > was a the result of the VFO 4th harmonic beating with the Xtal injection > osc. in the HFO module. I checked the response of the 3 section S-series > BPF that follows the HFO module and it looked just like it was supposed to > with over 80 dB rejection at the VFO 4th harmonic. Emmmmmm. I then began > checking osc. levels into the HFO TUF-1 mixer. The xtal osc. power > injection power measured +7 dBm and the VFO injection power -10 dBm. Should > be OK according to Wes's recommendation in EMRFD. However when I decreased > the level of the VFO power to -12 dBm, the offending spur disappeared off > the SA screen, ie. more than 80 db below the output carrier. > > I checked my Power meter calibration against my HP8640 so see if the power > meter was giving a correct indication of measured power and it was OK dead > on, ie. HP8640 set to -10dBm measured -1dBm on the Power meter at the VFO > freq. Not satisfied, I exchanged the TUF-1 for another one which I had in > my parts bin in case the the TUF-1 mixer was faulty. Same result. > > Conclusion: Be mindful of injection levels when using a double balanced > mixer especially for a transmitter and check the output with a SA before > using it on the air. > > Markus VE7CA > > > >
1410	2008-02-05 06:57:29	jr_dakota	Re: Digest Number 471
Speaking of your very nice 11 band transceiver, where did you get the information on those noiseless feedback amps (I hesitate to call them a Norton since they aren't common base) you use before and after the 1st mixer? I don't need a detailed rundown on them from you, just a point in the right direction to explore it further ... It looks to have all the advantages of the CB Nort
1411	2008-02-05 08:23:25	sm5glc	Re: Digest Number 471
JR I have a reprint from Microwave Journal May 1976 by David Norton: "High Dynamic Range Amplifiers Using Loss Less Feedback" It discusses both directional coupler feedback and the "usual" GB-transistor transformer coupled amp. If there is of any interest I can try to scan the pages.... /Lasse SM5GLC