Small Magnetic Loops
Of course I am very much interested in Wellbrook’s products, but when I saw its price quoted by an importing agency in Japan, I wondered hmmmmm…, it is quite a bit of investment for me who just came back to this hoppy after 30 years. I then encountered a “Do-It-Yourself” loop antenna, which was developed by a Japanese DXer Mr. Atsuhisa Kageyama, that would cost around $100 or even less. He has developed several versions of active loop antenna systems called “Delta Loop” (“Delta” is simply coming from that the loop is typically set in triangular shape as a convenient way). His information site is here (in Japanese language).
The “Delta Loop” Series developed by Mr. Kageyama
- Delta Loop-7 (Tunable type)
- Delta Loop-9 and 10 (Non-tunable type)
- Delta Loop-X (Hybrid of tunable and non-tunable types)
For the Loop-7 and Loop-9/10, the project book is available in bookstores in Japan, that comes with printed circuit boards of the amplifier and controller. The rest of the system is totally hand-crafted.
The loop wire is typically a 1 meter-sided triangle that can be easily assembled using PVC tubes. The system is based on differential amplifier and the noise level is very low. I also modified it into a portable style using a twin telescopic rod so that I can bring in my trip.
I found that the tunable Delta Loop-7 also performs nicely with a loop wire set inside car, even though the all doors were closed (the non-tunable type was not the case). See this page. This is useful for a discreet listening such as in crowded local park or sea-side area. One drawback is that the car engine has to be turned off to avoid suffering from the noise.
MFJ-1899T Whip Antenna
This whip antenna is originally developed for a tiny ham radio equipment FT-817 (Yaesu). Tuning is adjusted by telescoping of whip and plugging of jumper wire to the coil. I always use this whip when I drive to a local park to enjoy noiseless DXing. No amplifier is necessary and it can be easily set up and taken down using a magnetic base to mount on the rooftop.
PA0RDT Mini-Whip Antenna
This is an extremely small antenna. Many references are available online such as this site. I tested this antenna in several occasions and found that the performance is very much depending on locations. It was very noisy in city, but it worked nicely in suburban area, and I even felt it was similar performance to small loop. The best situation for me to use this antenna is when I am driving. Surprisingly the engine noise from my car does not affect to this antenna (not sure if this can apply for all types of cars). I assembled it in a short PVC pipe and mounted on the rooftop of my minivan. This is another style of discreet listening, but a good thing is that I can easily find my car in a huge crowded parking lot because of this mark. I enjoy listening to Radio Nacional da Amazonia on 11780 kHz while I am driving in Japan!
The following video is when I compared the effect of engine noise between this antenna and Delta Loop-7 that was set in the car.