Wednesday, February 10, 2010

BF981 VHF preamp

Not happy with the airband receiver and with some free time I decided to change the frontend mixer from the NE602 to an SBL-1; without any preamp the SBL-1 is only goo to listen to local FM boadcast stations or shortwave transmitters (the VFO Si570 kit can cover this large spectrum).

Decided to try an BF981 VHF preamp to put in place. Has I found out it's not easy to make the tuned circuits, I already had the same problem on the preamp for the NE602 mixer. Anyhow it's not complete since I drained almost completely the solar charged battery. Luckily it was only that, I tough I had blown ed the Si570 VFO kit since the display suddenly stopped working, only realized what happened after removing from the front panel and checking his voltage regulator.

The battery is getting each time less charger, I think it's due to winter covered weather and also for testing, I put the TM-D700 receiver on so I can check visually the transmissions, not the most practical way of testing preamps/receivers but there are no beacons on the airband with enough power to use as reference.

I am using ideas from the following schematics:

Anyhow at VHF things are not easy so will continue to learn a little more and make more tries in the following days... eventualy I will manage to make the latest greatest preamp.... :)

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