FC30-RT and FC30-BT Cheap Counters

[n5op]

I used to have an ancient B&K Frequency counter that I used to monitor the transmit frequency of my WRL Globe Champion 350. I've put a pickup loop below the chassis, in the output tank. It seems to work fine in that capacity. The old B&K has red LED digits, so I found a Chinese imprt counter, and FC30RT (R for red, B for blue). It's made for CB use, but spans 500 kHz to 50 MHz, and so I thought it should work well.

I found a mod recommended by W1VD that eliminates the preamp in the unit. Apparently, the preamp overloads easily generating harmonics and spurs. I found that the output voltage of my pickup loop is enough to cause these problems in my counter. "Great! That mod looks easy!" Sigh. It certainly would be if the unit I had were like the one used by W1VD. But his uses stuffed boards and mine is SMT. I think I found where the preamp is, but there are no part numbers and no schematic, so I can't be sure. 

I made a ~20 DB attenuator and put it at the input but that was too much, so I made it into made an ~10 dB attenuator. It's better, but the display still acts squirrely. This brings me to my question: does anyone else use one of these? How have you tamed the signal input so that the counter is solid? Also, does anyone know if there's a calibration procedure for this counter? I'd like to double check the calibration against a traceable 10 MHz source I have access to.

Kim N5OP

[N2DTS]

When I used to use a counter (I use the sdr-iq now) I just used a short antenna into the counter, it picked up enough signal from the TX antenna.

[Pete, WA2CWA]

The unit looks just like a Galaxy FC-347:
The manual: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CDoQFjAF&url=http%3A%2F%2Fwww.cbtricks.com%2Fradios%2Fgalaxy%2Ffc347%2Fgraphics%2Ffc347_om.pdf&ei=ohjPVJaWI8ylgwTjn4TYBw&usg=AFQjCNH4sCVyyRQ4-7-RmvHzDMozE9Egvg&cad=rja

[n5op]

Thanks! Yes, they are very similar and I think they're probably made by the same company, but the pictorial of the circuit board is different from what's in the counter I have.

Kim N5OP

[Opcom]

This is why I like the old ones with all separate ICs, no LSI. Every last thing is easy to get to. The problem with them now of course is some of the ICs are getting hard to find esp. in the DIP. However going back farther the display decoders can be made from gates, so all is not lost. The displays as well can be subbed. I've gotten surprisingly lazy and would probably just buy the modern POS model and throw it away when it breaks  Am I really lazy or just too busy with more important things than the level of technology in a commodity like a frequency counter?

[n5op]

Like me: far too busy with more important things!

Kim N5OP

[steve_qix]

I've got a number of FC30BT counters that I use in VFOs for class E rigs.  They work very well, at least in that application.  I think I'm putting a volt or two of RF into them.... have to look at the VFO schematic.  It's been a while since I've made a VFO.

[n5op]

I suspect that I have several volts and also suspect that the input impedance is quite high. I would like to find a manual for the thing along with some idea about how to make sure that the oscillator is running at the right frequency -- it seems to read high.

Kim N5OP

[Pete, WA2CWA]

If there is a product number on the main IC in the unit, maybe you can find the specification sheet. Sometimes on the spec sheet, they include a typical application circuit. Given the price, I find it hard to believe it's a overly complicated and sophisticated unique design.

[n5op]

Good points! I'll take a look. There are, maybe, two adjustments available on the board, so it can't be too complicated.

Kim N5OP