6496	2011-07-22 06:37:02	Tamás Fábián	Tayloe detector with diodes
Message	Date	From	Subject
Dear Group, few months ago I successfully built an SDR transceiver (It's one of YU1LM's). The hart of this receiver is of course a Tayloe detector implemented with some sort of analogue switching IC and divide-by-two ICs. The transceiver works from DC all the way to the high HF bands. The big dream of mine is being able to work CW / SSB up to the 2 meters band. As I figured out, the only limitation is the divide-by-two and the switching ICs. I don't really understand why "almost everybody" (based on the info that appears on various HAM radio web pages) trying to use canned (slow) switches instead of brewing one from fast shottky diodes. On the contrary, while very fast divide-by-two circuits are also hard to find, they probably even harder to homebrew. So the problem is to implement a fast divide-by-two circuit, or a 90 degree phase shifter that accurate and has a large frequency range. My questions are: - As I mentioned, I think it should not be particularly hard to homebrew a fast switch. Am I right? - Is there anybody who ever tried to (succeeded in?) building an SDR with a Tayloe (or whatever) style mixer for VHF / UHF? (Singe I/Q conversion, no downconversion before Tayloe stage) Was there exotic hardware involved? - Is it hard to build (or buy) a really fast (few GHz) divide by two circuit? - Is it hard to build a circuit that compares the phase of two signals and generates an error signal that can be used to adjust a phase shift network to achieve 90 degrees of phase shift in a broad range of frequencies? Thank you in advance, HA5FTL
6497	2011-07-22 06:53:37	Dan Mills	Re: Tayloe detector with diodes
On Fri, 2011-07-22 at 15:36 +0200, Tamás Fábián wrote: > As I figured out, the only limitation is the divide-by-two and the > switching ICs. I don't really understand why "almost everybody" (based > on the info that appears on various HAM radio web pages) trying to use > canned (slow) switches instead of brewing one from fast shottky > diodes. Some of those canned switches manage low single digit ns switching times (granted I am thinking about the single DPST stuff in SC70 packages). > - Is it hard to build (or buy) a really fast (few GHz) divide by two circuit? There are some very fast ECL parts out there but the logic levels are WEIRD. Don't forget also that as we are talking square waves here, you need board layout that can handle first 8 or 10 harmonics to get reasonable signal quality. > - Is it hard to build a circuit that compares the phase of two signals > and generates an error signal that can be used to adjust a phase shift > network to achieve 90 degrees of phase shift in a broad range of > frequencies? The phase comparator is called an xor gate (or a balanced mixer will do as well), RF phase shift networks are tricky if you want broadband and are usually best avoided. The easiest way to skin this cat is to use a pair of DDS chips fed from a common clock and just program the phase control registers differently, no fast dividers needed. Regards, Dan.
6498	2011-07-22 07:01:15	Lasse	Re: Tayloe detector with diodes
Dan Mills skrev 2011-07-22 15:52: > > There are some very fast ECL parts out there but the logic levels are > WEIRD. Don't forget also that as we are talking square waves here, you > need board layout that can handle first 8 or 10 harmonics to get > reasonable signal quality. > This might do in lower VHF: http://www.potatosemi.com/potatosemiweb/74Logic.html
6499	2011-07-22 07:45:45	Tamás Fábián	Re: Tayloe detector with diodes
Hi Dan, > - Is it hard to build a circuit that compares the phase of two signals > > and generates an error signal that can be used to adjust a phase shift > > network to achieve 90 degrees of phase shift in a broad range of > > frequencies? > > The phase comparator is called an xor gate (or a balanced mixer will do > as well), RF phase shift networks are tricky if you want broadband and > are usually best avoided. > > The easiest way to skin this cat is to use a pair of DDS chips fed from > a common clock and just program the phase control registers differently, > no fast dividers needed. > Wow. Simple, but effective. :) I'm wondering if two Si570 -s could be configured as such. Thanks! [Non-text portions of this message have been removed]
6501	2011-07-22 10:00:59	Dan Mills	Re: Tayloe detector with diodes
On Fri, 2011-07-22 at 16:45 +0200, Tamás Fábián wrote: > > The easiest way to skin this cat is to use a pair of DDS chips fed from > > a common clock and just program the phase control registers differently, > > no fast dividers needed. > > > > Wow. Simple, but effective. :) I'm wondering if two Si570 -s could be > configured as such. You could probably lock a Si571 to a Si570 in phase quadrature fairly easily, an xor gate between the two outputs will if lowpassed produce a tuning voltage for the 571 that will tend to Vcc/2 at 90 degrees. The details are left as an exercise for the student. The nice thing about a DDS pair as opposed to the Si570 is that you can supply an external clock that is common to both parts so with a little interconnection to sync the two chips internal states to make the IO_UPDATE happen synchronously (The chips have pins to do this), you can trivially program any phase offset you like. I have to admit to having been contemplating a direct conversion spectrum analyser done in exactly this way, get a baseband I/Q pair, digitise with a 24 bit audio AD (Actually gets maybe 20 bits!), then into a PC.... A linear 20 bit input is good for 120db total power range and by doing fft and averaging before taking the log performance should be respectable. Most of the RBW and VBW stuff could be taken care of at baseband (and quite a lot of it in the PC in software). Direct conversion makes the tracking generator output really easy, and with a little careful modulation of the TG output could even make a decent vector network tool. Anyone for a 1 eurocard spec. an with tracking generator (DC to say 250Mhz or so), not my current project, but maybe the one after next? Regards, Dan.
6502	2011-07-22 10:02:00	Tim	Re: Tayloe detector with diodes
If you want a 90 degree phase shift across a broad bandwidth, a quadrature divider (aka "2 stage johns
6504	2011-07-22 10:59:49	Tamás Fábián	Re: Tayloe detector with diodes
Dan, thank you again for the info. As searching for a suitable DDS I found that there are certain types (e.g. AD9854) that have quadrature outputs. Great. :) On 22 July 2011 19:00, Dan Mills <dmills@exponent.myzen.co.uk> wrote: > ** > > > On Fri, 2011-07-22 at 16:45 +0200, Tam�s F�bi�n wrote: > > > > The easiest way to skin this cat is to use a pair of DDS chips fed from > > > a common clock and just program the phase control registers > differently, > > > no fast dividers needed. > > > > > > > Wow. Simple, but effective. :) I'm wondering if two Si570 -s could be > > configured as such. > > You could probably lock a Si571 to a Si570 in phase quadrature fairly > easily, an xor gate between the two outputs will if lowpassed produce a > tuning voltage for the 571 that will tend to Vcc/2 at 90 degrees. > The details are left as an exercise for the student. > > The nice thing about a DDS pair as opposed to the Si570 is that you can > supply an external clock that is common to both parts so with a little > interconnection to sync the two chips internal states to make the > IO_UPDATE happen synchronously (The chips have pins to do this), you can > trivially program any phase offset you like. > > I have to admit to having been contemplating a direct conversion > spectrum analyser done in exactly this way, get a baseband I/Q pair, > digitise with a 24 bit audio AD (Actually gets maybe 20 bits!), then > into a PC.... A linear 20 bit input is good for 120db total power range > and by doing fft and averaging before taking the log performance should > be respectable. > > Most of the RBW and VBW stuff could be taken care of at baseband (and > quite a lot of it in the PC in software). > > Direct conversion makes the tracking generator output really easy, and > with a little careful modulation of the TG output could even make a > decent vector network tool. > > Anyone for a 1 eurocard spec. an with tracking generator (DC to say > 250Mhz or so), not my current project, but maybe the one after next? > > Regards, Dan. > > > [Non-text portions of this message have been removed]
6505	2011-07-22 11:34:59	AD7ZU	Re: Tayloe detector with diodes
> - Is it hard to build a circuit that compares the phase of two signals > and generates an error signal that can be used to adjust a phase shift > network to achieve 90 degrees of phase shift in a broad range of > frequencies? AD8302 will provide relatively accurate phase and amplitude measurement between 2 inputs. There are several VNA designs that have used this part. The phase measurement appears to be most accurate at the 90 degree point. 8302 has a built in reference which could be used to calibrate the inputs here is the info: http://www.analog.com/static/imported-files/data_sheets/AD8302.pdf I have not used this part but ran across the info a few months ago. Randy AD7ZU
6506	2011-07-22 11:53:55	dave	Re: Tayloe detector with diodes
I can do 70 cm with my UHFSDR. But, it doesn't use a Tayloe mixer. It uses DBM's. For the divider, I use MC10EP52 LVPECL dividers. They are rated to 4 GHz and cost about $4 each. Dave - WB6DHW <http://wb6dhw.com>
6509	2011-07-22 19:25:33	Ashhar Farhan	Re: Tayloe detector with diodes
There are several approaches you could take. The easy one is to use a transverter to get to 2M from your HF rig. That's the classic way to go higher in spectrum. From 2m onwards, coax can provide a very decent way to introduce phase lag. I used it as the only option available to me (I was doing it blind, without any instrumentation). Around 19 inch of coax should work (trim until you no longer hear the beat). There are several options on the analog side. Diode mixers with hybrid couplers are described by rick in emrfd in precisely such an application. That's my personal preference : to go analog as far as I can. There's yet another way to produce 90 degrees phase across a wide range. Simply lock a vco to your frequency source. The PLL, by it's nature provides 90 degree phase difference. I say 'simply' because it will probably work even with injection locking or first order loops. - farhan VU2ESE On 7/22/11, Tamás Fábián <giganetom@gmail.com> wrote: > Dear Group, > > few months ago I successfully built an SDR transceiver (It's one of > YU1LM's). The hart of this receiver is of course a Tayloe detector > implemented with some sort of analogue switching IC and divide-by-two > ICs. > > The transceiver works from DC all the way to the high HF bands. The > big dream of mine is being able to work CW / SSB up to the 2 meters > band. > > As I figured out, the only limitation is the divide-by-two and the > switching ICs. I don't really understand why "almost everybody" (based > on the info that appears on various HAM radio web pages) trying to use > canned (slow) switches instead of brewing one from fast shottky > diodes. On the contrary, while very fast divide-by-two circuits are > also hard to find, they probably even harder to homebrew. > > So the problem is to implement a fast divide-by-two circuit, or a 90 > degree phase shifter that accurate and has a large frequency range. > > My questions are: > > - As I mentioned, I think it should not be particularly hard to > homebrew a fast switch. Am I right? > - Is there anybody who ever tried to (succeeded in?) building an SDR > with a Tayloe (or whatever) style mixer for VHF / UHF? (Singe I/Q > conversion, no downconversion before Tayloe stage) Was there exotic > hardware involved? > - Is it hard to build (or buy) a really fast (few GHz) divide by two > circuit? > - Is it hard to build a circuit that compares the phase of two signals > and generates an error signal that can be used to adjust a phase shift > network to achieve 90 degrees of phase shift in a broad range of > frequencies? > > Thank you in advance, > > HA5FTL > -- Sent from my mobile device
6511	2011-07-23 03:27:25	Tamás Fábián	Re: Tayloe detector with diodes
> > There's yet another way to produce 90 degrees phase across a wide > range. Simply lock a vco to your frequency source. The PLL, by it's > nature provides 90 degree phase difference. I say 'simply' because it > will probably work even with injection locking or first order loops. > Farhan, I _almost_ thought about this, but instead of a complete PLL a phase comparator and a tunable phase shift network probably would do the trick. [Non-text portions of this message have been removed]
6512	2011-07-23 03:31:36	Tamás Fábián	Re: Tayloe detector with diodes
Dave, that's fine, I'm not insisting on tayloe mixers that much. The UHFSDR looks great, basicly the same thing I'd like to achieve in function. ;) On 22 July 2011 20:53, dave <dave@wb6dhw.com> wrote: > ** > > > I can do 70 cm with my UHFSDR. But, it doesn't use a Tayloe mixer. It uses > DBM's. For the divider, I use MC10EP52 LVPECL dividers. They are rated to 4 > > GHz and cost about $4 each. > > Dave - WB6DHW > [Non-text portions of this message have been removed]