A Novel Approach to a Multiband Transverter Design Jeff Kruth WA3ZKR Presented to the MUD 2010 Conference

Why a new transverter design? Are not the old ones good enough? Yes, but our nature is to experiment! New system level components offer greater flexibility (synthesizers!) Multiband operation is costly, yet desirable (Rovers, etc)! Some still like to homebrew….

Basis for Conventional Single Band TransverterApproach All communications is about filtering & noise rejection. Single band approaches minimize filter design/implementation difficulties. Clever use of hairpin/pipecap filter designs on FR-4 boards meet all requirement in a single band design. Can require significant real estate.

Local Oscillators: Problematic! LO is key component, used to be difficult, simpler with “building blocks”. Single LO Frequency – Easy to do w/ surplus PLO or Custom XO/Multiplier. Each band required a solution for the LO issue, many times not trivial to meet stability desired, etc.

Conventional RF Approach Basic RF Converter. No Amplifiers, therefore Bi-directional in signal path. Filters usually considered a necessity in RF & IF path for noise & image rejection. RF Filter IF Filter Narrowband Mixer & Associated LO

Typical M/W Amateur Transverter Features added for utility: IF Attenuator T/R Amplifiers IF Filter usually not needed, IF radio suffices Can remote LNA/PA, add line amp

Multi-Band Approaches Desirable to cover at least 2.3-10.368 GHz in one box (4 bands). Potential for significant size reduction. Front ends could be in box or remoted up tower. Use modern technologies to solve old problem! Cost savings is a possibility. Drawbacks include Higher complexity Single point failure, all bands off the air!

Multiband Issues Broadband mixer required, many types available 2-18 GHz, 1-15 Ghz, etc. Need Multiple LO’s, multipole switch. Multipole switch and multiple filters needed for RF side. Can be built up over time, but bulky, and LO’s may not be lockable to common reference.

Multi-band LO Requirements Previously a severe constraint! Prior schemes involved either PLO bricks or crystal multiplier schemes with different multiplication ratios. Availability of modern frequency agile synthesizers can change this! Currently L band .9-2 Ghz in sub-bands.

Multiband Design Improvements Use a synthesizer locked to a reference for stability issues. Use multipliers from old PLO blocks for LO multipliers for ease of implementation. Use a single electronically tunable filter for all band RF image reject task. Integrate a broadband amp and reversing switch for RF driver/line loss comp.

Multi-band Block Diagram Simple! LO’s can be added later YIG filter is fixed tuned SMA n-pole relays, cheap WJ, RHG, Add. Labs Anzac, M/A-COM Mxrs Multiplier Sections from old broken PLO’s

What’s this YIG filter thing? YIG tuned filters (YTF’s) key to M/W wideband receiver systems. Provide stable, easily tuned passband over multi-octave range. Made by wide variety of vendors! Real cheap at hamfests ($10-$100), if thrifty shopper! (I found 3 at M/W update) Need a “special” DC driver circuit? Not really!

More on YTF’s YIG material provides a magnetically tunable resonance at M/W frequencies. Magnetic field created by electromagnet in form of solenoidal pair. Current sets field hence frequency, so current source should be clean (low noise as possible) and stable (low DC drift). YIG sphere kept stable by small 24 VDC heater (150 mA)-not always needed. YIG magnet current typical 0-1A or less.

YTF’s, All Shapes & Sizes! Made by lots of folks for the last 50 years! Inside of all kinds of old M/W stuff! HP 8445A preselectors HP 8441 preselectors AILTech 707 SA RF Black boxes…..

Typical YTF Response YTF circuits inherently broadband. Yigs marked as octave typically broader Example is YTF used as 4-8 GHz, found to be 2-18 GHz.

Powering Up Your YIG! Many hams shy away as these seem too exotic. Driver circuit seems to be a stumbling block. Driver design sought that was very simple yet worked well. Decided on a cheap power OP amp!

YIG Driver Schematic Very simple circuit, needs good heatsink! Part is L165 5 terminal power op-amp. 5 watt low ohm stable R needed. Bi-polar supply, neg. is low current, DC-DC conv.

Datasheet for L165 Really nice power op-amp! Capable of 3 Amps! Less than 1A needed for us! Made by ST Micro- electronics.

Breadboard YIG Driver Obviously non-critical construction! Key was heatsinking both device and power resistor! Current can be sourced by either polarity supply by inverting drive voltage polarity.

Test Setup to Test Driver Simple to align, tune for peak output. Use power meter or crystal detector. DC voltage tuning approx. 0-3 V.

Filter Responses 2.3 & 3.45 GHz Simple, stable, easy to get filter shape!

Filter Responses 5.7 & 10.4 GHz Typical bandpass, approx 30 MHz wide

Converted Multipliers Bricks are cheap, esp. broken ones! Multipliers are simple, really don’t fail much. Old brick PLO is what dies. Simple to excise mult. Add SMA connector.

Performance of Multipliers Variety of bad bricks in Junque box. 3.3 & 5.6 were easy! Low drive requirements, high output power. 10 GHz from White box LO! (At last, its good for something…) +21 dBm drives from 1 GHz surplus amps.

Power In/Out for Multipliers 3312 MHz - +7 to +13 dBm out, 1104 in@ 15-20 dBm. 2 types for 5616 MHz: x4 & x5, x4 gave 9.5 dBm out for +20 in @ 1404, x5 gave +12 out for 1123.2 @+20 dBm. White box converted mult. X6, gave 10224 MHz @12.5 dBm for 1704 Mhz @20 dBm. No 2160 MHz Doubler tested, DBM?

The Guts of a 4 Bander Spread out on bench approx. 14 “ square Will pack up much smaller. Key is A32 synth. Can add multipliers as you develop them! Lock to a Rube? XO?

Final Thoughts! Presented to provoke experimentation with new (to us) approach. 2nd YTF could be used with untuned SRD Multiplier to make tunable LO as well. System would make a nice Noise Figure Meter front end for conferences….. Has potential to educate and provide utility! I recognize that this will not supplant traditional transverter approaches, merely complement them.

Questions? & Thank You for listening!