We received quite a few questions concerning the equipment used at 7QNL.
Below some information and (of course!) pictures.
Note: click on images to enlarge (as of May 27th we have internet again : -)
Besides the FT-857 (not D, but with a(n unused) D inside) and the power supplies
(for the FT-857 a 200W SMPS, and the amplifier a 1200W 48V SMPS) almost
all equipment is home brew. Yes, I know, a FT-857 may not be the most optimal choice
but this is what I had. The 300Hz (CW) and 2.3 kHz (SSB) filters help ; -)
I modded my FT-857 inside as the modulation of these rigs needs some ‘improvement’.
Below my headset, made of a 3.50 Euro headphone (this is one of the best headphones I
ever bought (honestly!) and an electret mic capsule with earplug foams to suppress ‘plops’..
Keyer: K3NG NANO keyer (Winkey compatible (with some patches by myself)
Logging software: N1MM (this package had no problems with my callsign: 7QNL)
RTTY software: mmTTY (embedded in N1MM <- works perfect!)
For this trip I built the ‘7QNL amplifier’ as I could get a HF pallet for a very good price.
Inside is also the remote Beverage switch circuit (right knob).
Btw, casing is home brew. ‘V-meter’ is multi meter (Vdd, Pout, Pref etc).
Antennas: I changed plan because of available material (bamboo and dead pine tree poles <- they are straight and high!) and the fact that I took five coax cables:
2 x 33m Aircell 7 (tnx PI4RCG) and 3 x ~25m H155 (tnx PA7FA).
10, 15, and 20m VDA’s were built ‘on the fly’ after 4NEC2 modelling. As I mentioned elsewhere on this site: these flabbergasting simple antennas work very well, are built within no time, and their construction is rigid due to the triangles in the diamond structure (contrary to e.g. Moxons, although VDA’s own the ‘Moxon effect’).
Fltr: 20m VDA, 15m VDA, 40m deltaloop, 10m VDA.
Made with (dry!) bamboo and/or dead pine trees (20m & 40m).
40m pole is 17m long and has three ropes @12, 14, and 16.5m.
For 40m the 14m rope is used. The deltaloop is forced towards
200 Ohms and matching is done with a 4C6 core 4:1-balun.
I prepared some brackets with N-connectors and ‘handy holes’ for the antenna
Pictures of ‘handy hole’ brackets for the 10 and 30m VDA feedpoints.
Red ropes are pull reliefs.
Common mode chokes were used at each feedpoint. Each ferrite clamp is 2 μH.
For 28 MHz 6 μH makes an Xl of >1 kΩ, which is more than enough (20 x Zfeed).
E.g. on 40 and 30m five clamps were used, resulting in Xl’s of 450 and 625Ω respectively.
A view towards the operation position with open amplifier (to adjust the
Beverage switching voltages after rolling out the Beverages):
Africa’s Finest … 7QNL !
Note the stone on the paddle to prevent it from walking away while keying ; -)
The amplifier has a hardware sequencer (to be 101% safe).
RX-antennas: Initially I targeted for 4 x 160m Bevs, but this appeared too long.
Our QTH is on a hill and rolling out the Bevs in the bush was a problem.
Moreover.. one Beverage was running through a small village and the local people feared
the wire. After negotiating with the people a compromise came out: 80m wire lengths were the limit.
Close up of a Beverage feedpoint (‘common mode’ choke ferrite clamps were
added later). Transformer consists of 3 stacked BN-61-202 (I believe) binocular cores,
winding ratio 8:3:
Crocodile clamps are very effective in the Malawi field!
Earth pins are 1.5m long iron concrete rods, bought and cut at the local market.
Remote Beverage switching box (with LM3914).
Yes, RCA connectors (low weight, and.. besides it’s for <10 MHz ;- ).
Feeding cable is very thin Pope 75 Ohm coax (tnx PI4RCG!).
Inside the Beverage switch box is a W7IUV preamp with a 2N3866 @75 mA
to compensate cable (~90m) loss.
In Holland I was informed that ~1 km of galvanized 2mm diam wire was
arranged. To be utterly sure that this wire could be soldered (easily) I
took some ‘S39’ (yes, the original!) soldering fluid… and put it in
a nasal spray/drop container. In Malawi I attempted to write ‘S39’ on it: