30 March 2017

Challenges of the HB100 10 GHz module

As listed in the previous post, the HB100 10 GHz sensor module poses some challenges when repurposed as an RTX. Let's list them, and possible workarounds.

1) The RF power is in the order of 10 mW (10-12 dBm).
On 10 GHz it is easy to assemble and use a high gain antenna. Some people report that an IKEA lamp has the perfect shape. Just remember that higher gain means narrower beamwidth.

2) Frequency stability was not a design goal for the original destination of use.
Frequency instability can be tamed with proper thermal insulation of the module. The more the merrier. In any case all narrow band modes are out of question. WFM is the way to go.

3) Receiver is direct conversion.
This one, combined with #2, is a bit harder to tackle. You can't do CW or SSB. You can't do FSK. The solution proposed by a U.S. HAM is to work full-duplex. Transmitters are on different frequencies. The received signal is then at an Intermediate Frequency equal to TXQRG difference. If the difference is about 88-108 MHz, you know which WideFM receiver can be used! Actually an RTLSDR dongle receiver allows more frequency agility and flexibility, thus allowing to operate I.F. outside the crowded FMBC band.

There are other reports that HB100 is sensitive to microphonics (mechanical vibrations are picked up and turned into electrical/RF signals). Not hard to keep under control, either.

29 March 2017

Easy way to 10 GHz

I read it on hackaday, then again on G3XBM's blog: there is an easy way to play with 10 GHz. And (very) cheap too!! The idea is to repurpose something originally meant to be used as something else. Like the RTLSDR TV dongles, the 74HC240 buffer and many more in this wonderful hobby.

The HB100 is a microwave sensor module designed to be used as motion and speed (doppler) detector. It operates on 10.525 GHz and can be retuned below 10.500 GHz into the 3 cm HAM band (Italian bandplan) with a screwdriver. It can be frequency modulated through the power supply (I guess you get some AM too). It features both the transmitter and the receiver, (patch) antennas included.

How much? Less than 3 EUROs including shipping. That's three espresso coffees standing in an Italian bar. Or three of the cheapest burgers in the "M" restaurant (their own definition, not mine).

Drawbacks (A.K.A. "challenges"):
1) The RF power is in the order of 10 mW (10-12 dBm).
2) Frequency stability was not a design goal for the original destination of use
3) Receiver is direct conversion

I have ordered 2 pairs and a spare one. I am curious how far the unmodified version will go.

By the way, I have spotted a similar radar device operating on 5.8 GHz and others on 24 GHz (InnoSent IPM165). Maybe ... ?

27 March 2017

UDN6118A VFD driver IC

I haven't tried it myself yet, but the (obsolete, discontinued) UDN6118A IC is an 8-line driver specifically designed for driving vacuum fluorescent displays. With two chips of these, up to 8x "7-segment + decimal-point" displays can be controlled through multiplexing.

Apparently UDN6128A and XO-951 are suitable replacements.

These IC's don't seem to be cheap either, but they do simplify wiring.