Improved Short Wave Loop Antennas for Qodosen DX-286 Portable Radio

[@englishrupe01]

Many thanks for the video. It is extremely informative. You have done done some great work there.

[@emctd9551]

I have done some more work with radio antenna improvements: 1. I measured the signal strength in AM medium waves band 520-1710 KHz with a modified radio (large 7" antenna bar) compared to the original DX-286 radio with a small 4" one. The modified radio had 10 dB higher signal strength (lower frequencies,) and 20 dB higher signal strength (higher frequencies). Ferritre bar size does matter! 2. I investigated why a large external loop antenna for SW band had much lower receiving noise than the built-in one. The sensitivity of the larger loop must be higher; that is science (see the video), but the noise was a mystery. The reason was in the fact that the 5" long twisted pair leads, connecting the tuning variable capacitor to the loop antenna and RF amplifier terminals, were unshielded. I did it on purpose, trying to minimize the stray capacitance to extend the maximum tuning frequency of the antenna, but that increased the noise coming from the digital radio PCBs. To provide the needed shielding, I took the shield sleeve from D=6 mm RF cable and placed it around the twisted pair, connecting the shield at only one point at the ground terminal of the RF amplifier. The result was stunning! The induced noise dropped by 10 dB or more. Now at the unfolded upper position of the SW loop antenna, its receiving noise is only slightly above the noise from the external loop antenna, rising by about 8-9 dB when the built-in antenna is in the down, folded position. Further noise reduction of the built-in antenna is a rather difficult task, requiring the shielding of the radio PCBs, and may be simply impractical.

[@mcdeadsquirrel]

Thank you very much for this. It's innovative and seems to work!!! Thank you from Upstate NY !!

[@emctd9551]

Thank you for the kind words! When I lived in Boston, I used shielded loop antennas to receive at night the European SW stations. Here in Sarasota, FL, except for a couple of propaganda SW stations broadcasting from Cuba and a few religious ones, there are no stations. Sadly enough, but even the large loop antenna can not bring up the DX stations here, they are all buried in noise. Probably building real full-size SW directional antennas is the only way to improve the reception, but this is not what I want to do. In some other places, the modifications that I suggest could make day and night improvements.

[@mcdeadsquirrel]

@@emctd9551 Yes, we are all in the same boat these days...on many occasions, I, too, can rec those Cubano stations with their propaganda as well as the religious stations. I will spend a few mins listening to the religious stations only to improve my poor espanol, One would think that the old powerhouses, viz the BBC, and all of the tropical band stations would start up again. The station that I miss the most came out of VZ, Ecos de Torbes. They have/had the greatest library of classical guitar music that I have ever heard. They would play it all night long. If you have any contacts down that way, pls let me know. best regards, lmc

[@Grandassets]

I am in Binghamton :) I bought a MLA-30, I replaced the thin stainless wire with a 3/8s copper HVAC tube

[@englishrupe01]

@@Grandassets I have a similar much cheaper (15 bucks) AliX version called the AMLA 150 and was thinking of using some old copper brake pipe that i have laying around. Did yours work out well?