EMRFD Message Archive 2090

Message Date From Subject
2090 2008-09-20 01:34:56 brainerd@wildblue... UHF-SDR Transceiver
I have finished a preliminary schematic for my UHF-SDR. It will use the Si570(LVDS or
PECL) to feed a pair of 4 GHZ PECL flip-flops to generate I and Q LO signals for a pair of
Minicircuits DBM's. It will cover from 1.8 MHz to 700 MHz(except a few holes the Si570
doesn't cover) with a power output of 100+ mW. Line in and Line out connections to a PC
sound card are utilized as in the Softrocks. A 1.7dB noise figure receive pre-amp is also
included. If interested please look over the schematic and the operaton document and pass
on any comments or concerns. I have not yet started the PCB layout. I like to try and get the
schematic as right as possible first.
The UHF-SDR documention is available from my "Under Development" page or directly at

Dave - WB6DHW
2094 2008-09-20 04:39:12 Eduardo Alonso Re: UHF-SDR Transceiver
Hello Dave,
Very nice ideas, but a little exotic parts used here.
I will study it...
73 Eduardo
2095 2008-09-20 10:53:17 Gary Johnson Re: UHF-SDR Transceiver

Looks do-able. Nice that you found a DBM with differential ports so you get a decent
drive level match with PECL drive. I think you'll want to study possible back-termination
mismatch between the mixer and the SY10EP52, since Zout on the PECL stuff is less than
50 ohms. That could result in all those complex and unpredictable re-mixing problems.
Also, the fast edges and ringing from that logic family will try to couple, mix, and radiate,
wayy up over 10 GHz. There's some tips on ECL-related matching in Howard Johnson's
books, though matching in a logic system isn't always so important as it is in a high-
performance RF converter. Micrel has SPICE models for their parts, but I always have to
call the app engineer and get him to email them to me. It's worth calling anyway, because
they have unpublished app notes for many of their parts and errata for datasheets that
doesn't seem to get into revisions.

Should T1 be a 3 dB hybrid? That gives you some isolation.

2096 2008-09-20 11:35:12 brainerd@wildblue... Re: UHF-SDR Transceiver
On 20 Sep 2008 at 13:39, Eduardo Alonso wrote:

> Hello Dave,
> Very nice ideas, but a little exotic parts used here.
> I will study it...
> 73 Eduardo
The PECL flip flops are available from DigiKey(I haven't checked Farnell or others). I also
got free samples from the Micrel site. The mixers are Minicircuits and can be oredered on-
line. The RF switches and the HMC482 mmic are from Hittite and they have on-line ordering.
The receive pre-amp is available from Digi-Key.

Dave - WB6DHW