[Philips210]

Hi

At long last, I'm now in a position to give an update on my loop aerial project.

I've completed the copper pipe loop aerial which I installed on the reverse side of one of my fence panels. It measures 1.5m x 1.0m.
In the aerial junction box, the paxolin tube that fits in the copper pipe was from a damaged luminance delay line from a RBM A823 colour TV. I stripped off the damaged windings and cut the tube to about 100mm in length. It fits perfectly inside the copper tube provided that any burrs are first removed from the copper pipes. As yet, I haven't tested this aerial but made a temporary aerial from some gash 2" x 1" timber. It's a frame of dimensions 1.0m x 0.8m. I wound some 6mm² mains cable around the frame and secured it with cable ties. The whole frame was then hung over a picture on a north facing wall in the lounge.

As you may recall, I built two amplifier boards, one using the Manhattan technique and the other a PCB from David's (G4EBT) design.
After a final inspection of the boards, I powered them up minus the loop aerial and monitored the supply current. The current drawn was around 90 to 100mA which seemed fine.
First off the 'Manhattan' board fitted with RCA 2N5109s. Excellent, it's working! and what lively performance on both MW and LW. Weak stations are brought to life and one thing that's really noticeable is the lack of interference that a long wire aerial suffers from.

Next, David's PCB to which I fitted turned pin sockets to try a variety of transistors. Thanks to David for going to the trouble of designing a PCB for this project which makes it somewhat easier to construct than the Manhattan technique. I first tried the Motorola 2N5109s. Excellent again, this board is working and marginally better performance than the RCA 2N5109s. I then swapped the transistors for 2N2219As, result poor performance so these won't be suitable. I then tried David's (Radio Wrangler) 4-247s (2N3866s) supplied by Graham (StationX) and the result was even better. I'm chuffed it's all working and I'm in the process of burying the 50 Ohm coax in some conduit under the garden path. Once everything is in place I'll be able to test the amps again with the outside copper pipe loop aerial.

Incidentally, the separate indoor junction box containing the choke, capacitor and LED + limit resistor I incorporated these components in a flush mount metal electrical box buried in the wall in a bedroom. A single blanking plate was marked out and drilled to take the BNC socket, 12V power socket and LED. So it's just a case of connecting a BNC lead from the wall plate to the radio and a 12V supply to the wall plate.

My initial tests were done on a Hacker Helmsman radio which has separate external aerial sockets for (1)MW/LW and (2)SW.

In my amplifier housing, which is mounted close to the loop aerial junction box, I've decided to do away with the BNC socket as it could be tricky to avoid the ingress of water. Instead, I fitted two cable glands located at the bottom of the box. One is for the coax cable back to the house, the other for the two single wires from the copper loop aerial. I used extra flexible wire for this to give reasonable durability. All four connections are by very small screw terminal connectors for ease of access and servicing. The amplifier housing has a rubber 'O' ring in the lid to provide a good seal against moisture. I've decided not to encapsulate the board but lacquer it instead. Fingers crossed, this should stand up to the weather. I used the same type of box on a water level indicator for a water butt that I built back in 2010 and it's bone dry inside.

Anyway, I'm extremely pleased with the results so far and I'll give a further update and some pics soon. I'm hoping to test the loop aerial on a Pye P93W/U radio. If I had a working comms receiver with an S meter I could provide more technically correct results. I could try monitoring the AGC line in the Hacker or the AVC line in the Pye, that's something to consider.

Regards
Symon