The 30m grabber has had several antennas tried on it. The magloop, which was OK, but it was insensitive due to its small size (1m) and was difficult to get up high due to its weight. A 8.2m vertical worked really well, but that was in use by other transceivers regularly. So now I'm going to try a small active antenna to see if the S/N ratio is good enough, the sensitivity is good enough and see how bad the usual problems with intermod and strong stations are with wideband amplifiers.
This design was proposed by IW4BLG here http://www.vlf.it/poggi4/stealthantenna.html
I didn't have all the fancy RF transistors, so I used S9018 RF transistors. I had to modify the final stage as the collector current was too high for the S9018 transistor. This was easy, just replace the emitter resistor with 470 ohm. At this time I had forgotten to alter the collector current in the first stage... this was because I misread a resistor as 910R instead of 10R, which satisfied me for current flow, but the mistake was noticed later by which point I had forgotten about the current. I put the correct resistor in and luckily, the current is within limits and it appears to be working OK. Signals are a down a bit however, so my modifications may have affected the performance.
The copper clad board was held in place by two ring connectors which had been snipped and bent into shape so they lay flat on the board and could be soldered.
In addition to the antenna plate, a short whip was added. The copper was saturated in SMT flux in an effort to keep away corrosion and oxidation from water. The PVC pipe enclosure was meant to be water tight, but I'm not convinced it is, or will remain so. (After rain I checked the pipe, water had collected in the bottom. I added a drain hole)
The antenna was placed near the end of one of my wire antennas, hanging off it and winched up meters high. Really it should be hanging further down a bit. I haven't tried high power on the wire antenna yet...
Whoops, acidentally transmitted into it by a rig being accidentally switched into TX when plugging it in, haha. This killed the coax driving transistor, and on top I also questioned whether the JFET was working properly. So I went back to basics with design suggested by PA0RDT for the Mini-Whip. http://www.radiopassioni.it/pdf/pa0rdt-Mini-Whip.PDF
I kept the coax driving transistor layout the same as before, S9018 with 470R emitter resistor. Then put the bias network and J310 JFET circuit as suggested by PA0RDT. I also replaced the straight whip with a longer, coiled 'whip'. (The following photo is with the coiled whip, but before replacing a significant amount of the RF circuit.
This is working better now, noise and signal levels are comparable on 80m, between my HF wire antenna and the active antenna. Slightly less S/N ratio on the active antenna but nothing hugely significant. It's now connected to the 30m grabber.
Here is a comparison of the grabber performance between the PA0DRT active antenna, G7FEK horizontal wire and 8.2m vertical antennas with all gain settings the same. The first 10 minutes is the active antenna, the next 4 minutes the wire and the next 4 minutes the vertical. Hmmm, now which has the best S/N ratio??
Here is the circuit diagram, courtesy of A4 and Pen and bad lighting. A tube is out in the shack.