Tag Archives: S082-0959

YTO YTF Driver: 0..250 mA, 16 bits resolution

Quick update on the YTO/YTF driver board – with 16 bits of resolution. Assembly, is complete, and basic function has been checked – digital control test will follow tomorrow.
Current is settable from 0 to 250 mA, with 65535 counts of resolution – about 3.8 Microamps per LSB. All has been build to minimize noise, with heavy filtering on the supplies. The DAC is run from a dedicated 5 V supply, with a 2.5 V precision reference, 1 ppm/K, MAX6325ESA+.
The U to I converter is powered by 11.4 V – provided by a LM317 voltage regulator.
Switching element is an IRF730, operated as a series variable resistance in series with the coil.

YTO YTF driver 2x250 mA 16 bit

YTO YTF driver 2x250 mA 16 bit schematic

Looking at the BoM, the parts sum up to about USD 35 plus board, not bad – target is to stay below about $100 for the final assembled unit, which will be achievable, no issue. Main cost comes from the MAX reference, and the DACs (DAC8830), almost USD 22.

To come: bandwidth testing

Figuring out the details of the Avantek S082-0959 YIG filter

For a small job, I need to design a digitally-controlled YIG preselector (a high-performance bandpass filter), for the 12.4 to 18 GHz range. The application is related to a test rig, and only 4 units are needed – at low cost, and controllable by USB. The control will be easy enough, just a programmable current source and some parameters, but first, finding a suitable YIG is quite a challenge – either only single pieces are available surplus, or they are new, and prohibitively expensive.

Remembering some earlier work, I had a look at the S082-0959 – these were made by Avantek, and are available, scavenged from old spectrum analyzers, for about 200-300 USD each, and still have one spare around here. The S082-0959 is also known as YF85-0107, or HP 0960-0473 (pinout may vary).

To get started, first the basics need to be figured out. Tuning sensitivity, bandwidth roll-off (need at least 12 dB/octave; and >50 dB spurious).
The thing has two pairs of connections: heater (2 wires) and coil (2 wires, this sets the magentic field – the tuning, via current – not voltage – control).

Looking at some spectrum analyzer schematics – the heater needs about 28 V. And, in fact, it works well and heats up quickly, drawing about 80 mA at 28 V, less with strong coil current applied (more during heating-up).

YIG filter Avantek S082-0959

The test setup – two power supplies, a counter EIP 545A, a microwave source EIP 928, and a microwave receiver Micro-Tel 1295. Signal level was 0 dBm.
The coil supply has a 4.7 Ohm current sense resistor, I’m measuring the voltage drop to calculate the current.

For 10 GHz, the tuning current was found to be about 132 mA, about 75.8 MHz/mA sensitivity.

Measurement result of insertion loss vs. frequency –
s082-0959 yig insertion loss vs frequency at 132 mA
– note that the passband is not well captured, but 3 dB bandwidth has been measured, by manual tuning, about 25-30 MHz. Recordering accurate values is a bit troublesome, would need to phase-lock the microwave source and receiver.
There is a spurious signal, about 350 MHz above the center frequency. This I will need to investigagte further. Note that the measuement points are not arbitrarily selected, but the YIG was actually tuned for the minimum loss, and the maximum response of the spurious.

Calculating the roll-off (25 MHz assumed 3 dB bandwidth):
s082-0959 yig roll-off at 10 ghz

As you can see, when doubling the bandwidth (e.g., from 2x to 4x – don’t look to close to the center frequency), the signal is about 20 dB down. That’s close to 18 dB per octave.
Without going into theory, which can be found elsewhere, a one-stage YIG filter will give (ideally) about 6 dB per octave. So the S082-0595 is most likely a 3 stage (3 sphere) filter. Well, limited accuaracy – the YIG will be fully characterized, once things are more advanced.