EMRFD Message Archive 9823

Message Date From Subject
9823 2014-03-15 10:20:47 sohosources Binaural Weekender?
Hi, gang,
Thinking about building a binaural weekender (BW), and I have a couple questions:
If anyone happens to know:

1. Can KK7B's Binaural RX receive SSB and AM? I *know* it can RX CW, I suspect it can RX SSB, and I'm hoping for some facility with AM...

2. The QST BW is set up for 40 meters, but in case I'd like to try other freqs, are the front-end and LO phase splitter Ls and Cs scalable? If so, are there "hard equations" or can I simply scale arithmetically?

3. Can I optionally pass the I/Q audio to SDR software for computerized demod, or is the phase accuracy between the channels too "loose" for SDR (but just fine for between the ears)?

Perhaps I'm way left of center, but I'm thinking about building a 9-MHz BW so I can experiment with it as the IF/audio sections of a Progressive RX, or with an FCC-2 DDS-controlled converter/mixer.  

Thanks, as always,

--Kirk, NT0Z
 
9824 2014-03-15 10:54:17 Thomas S. Knutsen Re: Binaural Weekender?





1. Can KK7B's Binaural RX receive SSB and AM? I *know* it can RX CW, I suspect it can RX SSB, and I'm hoping for some facility with AM...

SSB is no problem.
 


2. The QST BW is set up for 40 meters, but in case I'd like to try other freqs, are the front-end and LO phase splitter Ls and Cs scalable? If so, are there "hard equations" or can I simply scale arithmetically?

The equations are both shown in ch. 9 of EMRFD and in the hybrid coupler paper on the CD with EMRFD. 


3. Can I optionally pass the I/Q audio to SDR software for computerized demod, or is the phase accuracy between the channels too "loose" for SDR (but just fine for between the ears)?

It should not be a problem, you may want to take the I/Q baseband signal after the first amplifier, other than that, make sure your audio soundcard have stereo input, most microphones are mono input. 
 
73 de Thomas LA3PNA.

--

 Please  avoid sending  me  Word  or  PowerPoint  attachments.
 See  <http://www.gnu.org/philosophy/no-word-attachments.html>
PDF is an better alternative and there are always LaTeX!
9825 2014-03-15 23:38:49 radioaustralia123 Anyone a circuit for a Active High Impedance Scope Probe..?
Hi,

Does anyone have a good circuit for a home built “Active High Impedance Oscilloscope Probe”? Looked on Ebay and they are expensive.

Thanks,

Roderick Wall, vk3yc.
9827 2014-03-16 04:34:58 NeilDouglas Re: Anyone a circuit for a Active High Impedance Scope Probe..?

Roderick,

 

What sort of bandwidth are you looking for?

 

NeilD

G4SHJ

 

9828 2014-03-16 05:50:11 radioaustralia123 Re: [emrfd] Anyone a circuit for a Active High Impedance Scope Probe
Hi Neil,

My need at this time is up to 50MHz. But anything above that would mean I could use it at VHF if ever required. Or even higher if possible.

Roderick.

9829 2014-03-16 05:57:23 Eamon Egan Re: Anyone a circuit for a Active High Impedance Scope Probe..?

The late and lamented Bob Pease shows how to build a jfet probe with a loading of 1-2pF of capacitance in parallel with 10^11 ohms.

 

If you Google “pease jfet probe” you may get a Google Books hit to page 16 of “Troubleshooting Analog Circuits”. This book is well worth buying in my opinion, if only for the humour and anecdotes.

 

Otherwise, you can find the same circuit on page 12 of a collection of his EDN articles which you can find here (another Google hit on the same search): http://www.introni.it/pdf/Bob%20Pease%20Lab%20Notes%20Part%208.pdf

 

Eamon

VE2EGN / AB1NK

 

 

9830 2014-03-16 06:25:55 Harold Smith Re: Anyone a circuit for a Active High Impedance Scope Probe..?
I wrote an article for QRO Quarterly a few years ago on the one I use.  I don't remember which issue.

Input Z is, IIRC, 100k in parallel with <0.5 pF.  Bandwidth is over 100 MHz.  One JFET and a couple of emitter followers.

de KE6TI, Harold


9831 2014-03-16 07:37:48 NeilDouglas Re: Anyone a circuit for a Active High Impedance Scope Probe..?

Roderick,

 

I built this, but I used a LM7171 as my output amplifier.

 

http://oliverbetz.de/pages/Artikel/Simple-High-Impedance-Probe

 

I made C1 adjustable; adjust with a square wave for best waveform.

 

Neil

 

9832 2014-03-16 10:53:55 Joshua Lynch Re: Anyone a circuit for a Active High Impedance Scope Probe..?
Hi Roderick,
I built this one last year for my spectrum analyzer, but I think it would work just fine for an o'scope. It's based on the OPA656.

http://www.edn.com/design/analog/4322333/High-impedance-FET-probe-extends-RF-spectrum-analyzer-s-usable-range

It has a passband of 10Hz - 200MHz at -3dB.

I designed a board for it as well, and I have a extra hundred unpopulated boards. If you're interested I can send you a few; all you'd have to do is order the parts and solder them on.


--josh



9833 2014-03-16 13:36:45 kerrypwr Re: Binaural Weekender?
G'day Josh.

I've been thinking about a FET probe for a long time; a couple of your boards would motivate me!

I'm happy to pay for them + postage to VK; you probably have a Paypal account.

Kerry VK2TIL.
9834 2014-03-17 13:52:38 John King Re: Anyone a circuit for a Active High Impedance Scope Probe..?
Harold:
 
I have a listing of QRP Quarterly articles prior to 2010.  It shows that you wrote an article entitled "Homebrew High Frequency Low Capacitance Probe" for the Fall 2007 issue.  Is that the one to which you were referring?
 
John, W5IDA
9835 2014-03-17 14:54:44 Harold Smith Re: Anyone a circuit for a Active High Impedance Scope Probe..?
John,

That's it.

Harold


9836 2014-03-17 15:37:58 radioaustralia123 Re: [emrfd] Re: Anyone a circuit for a Active High Impedance Scope P
Hi John,

Is there a website where I can download this article?

I’ve Google the Internet but can’t find it.

Thanks,

Roderick Wall, vk3yc.

9843 2014-03-19 13:19:43 radioaustralia123 Re: Anyone a circuit for a Active High Impedance Scope Probe..?
Hi Josh,

Thanks for your offer for the PC Boards. When I received your 1st email from the group I was about to leave home. So I quickly saved the article and missed reading your offer for the PC Board. Things have been a bit hectic here.  In response to your 2nd email offer I have sent you a personal email. Thanks very much for your kind help.

Regards,

Roderick Wall, vk3yc.
9844 2014-03-19 14:57:38 radioaustralia123 Re: [emrfd] Anyone a circuit for a Active High Impedance Scope Probe
Hi NeiI,

Thanks for your help,

Roderick Wall, vk3yc.

9845 2014-03-19 15:05:34 Dave Daniel Re: Anyone a circuit for a Active High Impedance Scope Probe..?
Yes, when I started building my lab (a long time ago) a took to heart Jim Williams' comments in his article about home labs and have tried to stick to instruments which I can repair. I deviated from that when I bought my first 7904, but since then I have learned that the 7xxx 'scopes are also repairable (in no small part due to the expertise of the members of the Tektronix forums and their willingness to help).

DaveD

9850 2014-03-21 15:51:41 radioaustralia123 Re: [emrfd] Anyone a circuit for a Active High Impedance Scope Probe
Hi all,

You may find this interesting.
I found the following for a high Z probe. It has a interesting front end with a divider for 10Mohm with a tap at 2Mohm. The TI OPA IC opamp is used as a buffer. With a 50ohm load and 50ohm source it ends up as a 10:1 probe.

Looks like a lot of work has been done with a number of measurements on the probe (72 pages). My problem is that I can’t read German. I’ve asked the author if there is a English version, but the reply was no.


I’m thinking that this front end circuit maybe used with Josh’s PC Boards?


Roderick Wall, vk3yc.
9865 2014-03-24 14:31:01 ehydra Re: Anyone a circuit for a Active High Impedance Scope Probe..?