I opted for the Jensen on RX. It has a very wide and flat response curve with minimal changes to phase. It ain't cheap!
See the data sheet: http://www.jensen-transformers.com/datashts/dm2xx.pdf For TX, where the low end response is not as critical, I used EBTECH Hum Eliminators that have a 20Hz to 70 KHz frequency range http://www.ebtechaudio.com/llsheinf.pdf -Tim ----- Integrated Technical Services -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of kd5nwa Sent: Tuesday, January 23, 2007 1:43 PM To: Flex Radio Subject: Re: [Flexradio] Spur on AM You can also have 60Hz/50Hz hum and harmonics from having ground loops which the transformer eliminates. The DC offset of the soundcard or picking up the LO causes the narrow spike at the center of the pass-band, but sometimes you also have a hump that is fairly wide and slowly decays, a lot of that is hum and harmonics. At 11:51 AM 1/23/2007, you 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/ > >FlexRadio Homepage: http://www.flex-radio.com/ > > > >FlexRadio Knowledge Base: http://kb.flex-radio.com/ > > > > > > > > >-------------- next part -------------- >An HTML attachment was scrubbed... >URL: >http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachmen ts/20070123/c62f16a9/attachment.html > >_______________________________________________ >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/ Cecil Bayona KD5NWA www.qrpradio.com www.hpsdr.com 'Never argue with an idiot. They drag you down to their level then beat you with experience.' _______________________________________________ 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/
