I am getting excellent results with the RS units. The transmit rejection adjustment is just like it was without the isolation transformer nulled out to 0.00 phase and 0.00 gain using my TS-850 as the RX. 30db over S9 on LSB and S4 on USB on the 850 with the Flex transmitting on LSB with the test tone. I'm real happy with that. I am using the D44 card. Eric has said before that the D44 should not need any TX compensation and mine doesn't. The receiver is also sounding great. No more 11khz hump in the panadaptor and I'm not noticing and anomalies in the RX. If anything it may be a bit quieter. Well worth the 32 some odd bucks. No way I'll spend $350 on Jensen's. I am using a Jenson from my audio rack to the Flex however. Frank WY3D ----- Original Message ----- From: Tom Thompson To: Jeff Anderson Cc: FlexRadio@flex-radio.biz Sent: Tuesday, January 23, 2007 11:32 PM Subject: Re: [Flexradio] Spur on AM
Hi Jeff, Thank you for your thorough analysis. I looked for some specs on the RS units but found none. I did find some 1:1 transformers in the Digikey catalog that had a 10K impedance (part # 237-1151 for $17). These transformers had 2-db cut offs at 300 Hz and 100 KHz. I then looked up the Jensen units that Tim uses. These specs are spectacular with 3-db points at 0.1 Hz and 15 MHz and less than 0.5 degrees deviation from linear phase from 20 Hz to 20 KHz. The maximum THD is less than 0.03%. They are designed to drive 20 K ohms while being driven from 600 ohms. The price is over $100. I think that the results are going to vary depending on the transformer just as Jim predicted. 73 Tom W0IVJ Jeff Anderson wrote: >Hi Tom, > >I believe the bandpass will depend, in part, on the >input impedance of the device to which it's attached. > >Many months ago I measured the passband of one of >these devices for a friend who had terrible hum with >her stereo and wanted to use one of these, and it was >flat out to 50k (which was the limit of my dsp-based >measurement system) into the fairly-high impedance of >the measurement system and using a low output >impedance white-noise generator as the source. > >I just took a look at the low frequency performance on >my sdr1k with the RS isolator and my Delta 44. I fed >the SDR with white noise (from an old GR noise >generator that I use expressly for this sort of >thing), and I expected to see a "notch" on the >display corresponding to the device's low frequency >cutoff. Suprisingly, even at max Zoom In (6 >Hz/pixel?) and with the display shifted so that the IF >0 frequency was centered in the display, I think I >*might* have seen the *hint* of a notch. > >Another negative that I did see, though, were some >distortion products that became visible as one sweeps >a generator (I used my 8640b) through the IF "0" >frequency. I did not see these when the isolator was >*not* in-circuit. But they seemed to disappear pretty >quickly as I moved the generator away from the IF 0 >frequency, so these may not be a significant issue, >or, perhaps, only an issue for signals near the (now >much attenuated) "hump." But this raises a point >worth noting: additional devices in the audio path, >such as the gnd-loop-isolator, could add some amount >of distortion to the receive signals. > >- Jeff > >--- Tom Thompson <[EMAIL PROTECTED]> wrote: > > > >>Jeff, >> >>What does the bandpass of the isolator look like >>compared to what we are >>trying to pass? I am sure that a better transformer >>could be had if it >>would help. As far as the hump is concerned, isn't >>it just those >>frequencies close to DC that cause it? >> >>Tom W0IVJ >> >>Jeff Anderson wrote: >> >> >> >>>I just made a few more measurements using my Delta >>> >>> >>44 and some of my test >> >> >>>equipment. Adding in the ground-loop isolator to >>> >>> >>the Line-In path has the >> >> >>>following effects: >>> >>>Positive: >>> >>>1. Noticably reduces the IF "hump". >>>2. "Flattens" the display (w/o the isolator, I see >>> >>> >>a bit of rolloff towards >> >> >>>the display edges when in 0.5x zoom mode. >>> >>>Negative: >>> >>>1. Image rejection worsens at the display edges. >>> >>> >>That is, if a strong >> >> >>>signal is in the receive audio passband (I used a >>> >>> >>-40 dBm signal) and you >> >> >>>null its image down to the noise-floor, if you then >>> >>> >>shift the frequency of >> >> >>>the received signal (but not the receiver's VFO-A >>> >>> >>frequency), you'll see the >> >> >>>image begin to reappear. If the signal is moved in >>> >>> >>frequency such that the >> >> >>>image is at the edge of the display (again, in 0.5x >>> >>> >>zoom mode), it appears >> >> >>>to me that the image rejection is about 10 dB worse >>> >>> >>*with* the line >> >> >>>isolator. In other words, it's in the mid to high >>> >>> >>30's (of dBs) instead of >> >> >>>the mid 40's. (Note, though, that in either case, >>> >>> >>the image can be nulled >> >> >>>down to the noise). >>> >>>I'm not sure that the positives outweigh the >>> >>> >>negatives, but it raises some >> >> >>>questions: >>> >>>1. Can an "isolator" be designed, in hardware, to >>> >>> >>maximize the positives >> >> >>>and minimize the negative? >>>2. Could a filter be designed so that, when it's >>> >>> >>convolved with the input >> >> >>>signal, we maximize image rejection across the >>> >>> >>whole display, and not just >> >> >>>at the frequency for which the image is nulled. >>> >>> >>That is, can the "bowl" >> >> >>>shaped response to image rejection (when viewed >>> >>> >>across the entire display) >> >> >>>be flattened? If so, how could this be done. (And >>> >>> >>what's the plan >> >> >>>regarding the use of the pulse generator that's in >>> >>> >>the hardware?) >> >> >>>- Jeff, K6JCA >>> >>> >>>-----Original Message----- >>>From: [EMAIL PROTECTED] >>>[mailto:[EMAIL PROTECTED] Behalf >>> >>> >>Of Tim Ellison >> >> >>>Sent: Tuesday, January 23, 2007 7:29 AM >>>To: Joe - AB1DO; FlexRadio@flex-radio.biz >>>Subject: Re: [Flexradio] Spur on AM >>> >>> >>>When I added a Jensen line isolator to my system I >>> >>> >>did notice that the >> >> >>>noise floor dropped by a few dB after recalibrating >>> >>> >>I/Q along with a >> >> >>>very noticeable decrease in the 0 IF noise hump. >>> >>>-Tim W4TME >>>----- >>> >>>-----Original Message----- >>>From: [EMAIL PROTECTED] >>>[mailto:[EMAIL PROTECTED] On Behalf >>> >>> >>Of Joe - AB1DO >> >> >>>Sent: Tuesday, January 23, 2007 10:03 AM >>>To: FlexRadio@flex-radio.biz >>>Subject: Re: [Flexradio] Spur on AM >>> >>>Bob, >>> >>>yes, I did need to redo an image reject >>> >>> >>calibration. But after that, the >> >> >>>result was as stated. >>> >>>73 de Joe - AB1DO >>> >>> >>>Bob N4HY wrote: >>> >>> >>> >>> >>> >>> >>>>Are you guys saying that you did not need to >>>> >>>> >>change the IQ balance >> >> >>>>settings at all? Amazing. >>>> >>>>Bob >>>>N4HY >>>> >>>> >>>>Joe - AB1DO wrote: >>>> >>>> >>>> >>>> >>>>>Jeff, >>>>> >>>>>fascinating. I tried it here also and indeed the >>>>> >>>>> >>hump is all but gone >> >> >>>>> >>>>> >>>>> >>>>> >>> >>> >>> >>> >>>>>using the RS 270-054 on line-in. Now I always >>>>> >>>>> >>thought that only a >> >> >>>>> >>>>> >>>>> >>>>> >>>high >>> >>> >>> >>> >>>>>spec audio isolator (as in handles way above >>>>> >>>>> >>audible frequencies >> >> >>>>> >>>>> >>>>> >>>>> >>>well) >>> >>> >>> >>> >>>>>would work on the input given the I/Q spectrum >>>>> >>>>> >>is about 90kHz wide >> >> >>>>> >>>>> >>>>> >>>>> >>>at a >>> >>> >>> >>> >>>>>sampling rate of 96kb/s (I am using the >>>>> >>>>> >>Delta-44). But I closely >> >> >>>>> >>>>> >>>>> >>>>> >>>compared >>> >>> >>> >>> >>>>>the panadapter with and without the isolator and >>>>> >>>>> >>I see no difference >> >> >>>>> >>>>> >>>>> >>>>> >>> >>> >>> >>> >>>>>other than the DC hump. What am I missing? >>>>> >>>>>73 de Joe - AB1DO >>>>> >>>>> >>>>> >>>>> >>>_______________________________________________ >>>FlexRadio mailing list >>>FlexRadio@flex-radio.biz >>> >>> >>http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >> >> >>>Archive Link: >>> >>> >http://www.mail-archive.com/flexradio%40flex-radio.biz/ > > >>>FlexRadio Homepage: http://www.flex-radio.com/ >>> >>>FlexRadio Knowledge Base: http://kb.flex-radio.com/ >>> >>>_______________________________________________ >>>FlexRadio mailing list >>>FlexRadio@flex-radio.biz >>> >>> >>http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >> >> >>>Archive Link: >>> >>> >http://www.mail-archive.com/flexradio%40flex-radio.biz/ > > >>>FlexRadio Homepage: http://www.flex-radio.com/ >>> >>>FlexRadio Knowledge Base: http://kb.flex-radio.com/ >>> >>> >>>_______________________________________________ >>>FlexRadio mailing list >>>FlexRadio@flex-radio.biz >>> >>> >>http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >> >> >>>Archive Link: >>> >>> >http://www.mail-archive.com/flexradio%40flex-radio.biz/ > > >=== message truncated === > > > > > > -------------- next part -------------- An HTML attachment was scrubbed... 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