Thanks, Ron and Lee for the information. It's helpful. Were I'm at is that there IS a noticable difference in my rigs. I started with both RXs aligned by the book, with an HP 8656B signal generator. I noticed right away that the R7A "seemed" much more sensitive - reading 1-2 S units higher on signals, and the local noise floor sounded much louder. The TR7 actually does better by the numbers, MDS and 10 dB S+N/N sensitivity actually measures better on the TR7, which I had modded earlier with Schottkey diodes in a couple of the mixers as suggested by SM6RPZ here: http://www.homer.se/radio/mod7.php . I went back over the AGC/S-Meter adjustments in both manuals, and noticed some differences and an anomaly that I later found was addressed here back in 2005 by Lee.
I think the problem may revolve around proper setting of the IF gain control. The TR7 manual is pretty vague about this, but mine was maxed out, I think by a previous tinkerer. The R7 manual is more specific. The IF gain adjustment is also in a different circuit location in the TR7. The TR7 manual states that the S-Meter should read S-9 at about 30 uV, and the reference at http://www.zerobeat.net/drakelist/tr7bookalign.html suggests 30 to 50 uV (-73 to -77 dBm) for S-9. This seems reasonable. I was measuring 100 to 200 uV for S-9 on both rigs when adjusted "by the book". I've been trying to work out the differences in the adjustment procedures (including the tr7bookalign document) between rigs, to come up with a homogenized procedure that works well for both. I came across Lee's discussion of the missing R1127 adjustment for the R7 after I had devised my own method. I'm closer than before, S-Meter readings are closer to each other and to the desired 30-50 uV for S-9, but the local noise floor is still higher on the R7 than the TR7 (S-8 vs. just under S-5) and still sounds louder. I seem to have about 4 dB drop through the splitter in the R7, which seems reasonable. I've also discovered that for best accuracy in adjustment, the R7 antenna selector should be set to Main/Alt - I didn't see this mentioned in the manual. All sensitivity measurements and adjustments have been done with the 2.3 KHz filter switched in. All oscillators in both radios have been set "spot on" with a freshly calibrated freq counter. So, I'm back at it. I will hopefully have another TR7 coming in today or tomorrow from an estate purchase, which should be dead stock and still have the factory alignment. I'll see how it measures up before I touch anything. TNX es 73 -Jim (maybe I'm just too darn picky) NU0C On Mon, 1 Dec 2008 06:33:51 -0500, Ron Baker wrote: >Hello Jim, well I have both the R7A & the TR7A mated >together and I see very little if any difference in the >receiving capability of either unit. The R7 is basically >the same as the receive section of a fully loaded TR7, but >with a few minor exceptions like the notch filter and noise >blanker upgrade. The ability to switch between >receivers is nice if you need that but for a typical QSO >having the twins is no real advantage. I do notice with >my setup if you don't have all three oscillators set >perfectly in both units, in transceiver there could be an >offset in frequency between receive and transmit. Both >units interconnect the VFO and 40Mhz master oscillator >signals to sync together but there are two more crystal >oscillators in each unit that could be off a little to cause >the offset. > >Overall, having both pieces is nice to have if you want the >entire station but no real noticeable difference in the >basic receiving capability of either unit. > >Ron / WB4HFN > > > >-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Jim >Shorney >Sent: Sunday, November 30, 2008 11:29 PM >To: drakelist@zerobeat.net >Subject: [Drakelist] 7-twins receiving together > > >Hi Gang, > >I'd like to get some subjective impressions from 7-line >twins owners on how the two receivers compare to each other >when wired up in transcieve configuration. I know the R7 >isn't *exactly* the same as the TR7 RX, and there is some >loss through the R7 antenna splitter. I would just like to >hear some opinions on how they differ in real world >performance when connected together. (Yes, I cut the jumper >in the TR7...). > >Is there anyone out there? > >TNX es 73 > >-Jim >NU0C > > > >_______________________________________________ >Drakelist mailing list >Drakelist@zerobeat.net >http://mailman.zerobeat.net/mailman/listinfo/drakelist > _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
