There is no external antenna input on the PL-380. The DSP chip needs an inductor for AM/LW and a whip/wire for SW. The details are in the documentation at Silicone Labs website.
---In ultralightdx@..., <kugellager@...> wrote:
I don't think he is talking about directly soldering wires to the PL-380 antenna inputs. I think he is trying to match his 50 ohm coax to the input impedence of the antenna input using a torid matching transformer.
For example, I have a Rycom 1307A-GR which I use for my non-ultralight LW DX. Its RF input impedence is not the typical 50 ohm input but is a 3000+ ohm input. To match my 75 ohm RG6 Quad shield coax to the 3000 ohm input of the radio I need a matching transformer that gives me aobout a 40:1 RF ratio. For this I use a FT140 type J toroid with 38T:6T giving me about a 40:1 RF ratio.
This isolates the coax from the radio but still matches the two different impedences allowing for maximum signal transfer from the coax to the radio.
I think this is what Hans wants to do.
So the question is: What is the input impedence of the PL-380 antenna input? It seems like since it is a variable matching circuit there must be some ideal middle value impedence he can use to match the coax to the radio.
I would actually like to do this as well so that I do not have to lug around a fragile ferrite rod loopstick to inductively couple an external antenna as I do now. Internal antenna has been removed..
John
];')
---In ultralightdx@..., <hans.ostnell@...> wrote:
You're absolutely right, Rick. The best results I've achieved with the Quantum loop + PL-380 combo is when the Quantum is inductively coupled to the 7.5" loopstick on the modified PL-380, by means of the Quantum coupler. This works excellent.
Hans
Vardo isl. Arctic Norway
---In ultralightdx@..., <n3ikq@...> wrote:
I'm not sure I understand exactly what you are doing but be VERY careful if you are connecting an external signal directly to the solder pads where the loop wires go. Go to Silicone Labs website and download the documentation for the Silicon Labs si4734 chip. You will notice that the loopstick forms a resonant circuit with varicaps embedded in the chip. To tune the radio the DSP changes the capacitor value effectively resonating the tank circuit to the desired frequency. In other words, the radio has its own internal tuned loop circuit. Attaching any high level signal in place of a loopstick seems dangerous. Additionally, there are many ESD warnings to the possibility of zapping the chip at the antenna input unless an external capacitor is used for protection when bringing in external signals. Indirectly coupling a signal into the original or supercharged loopstick seems to be the best and safest way as far as I can tell. Rick
---In ultralightdx@..., <hans.ostnell@...> wrote:
Group,
Anyone who could suggest a matching transformer to use when connecting the 50 Ohm output from my Quantum QX-loop directly to the PL-380?
What I'm doing now is to switch between the 7.5" loopstick and the QX-loop. The QX works pretty good together with the 380, actually, but I can see that I'm not taking full advantage of the QX sensibililty (i.e I loose gain from the loop when connecting it diretly to the ferrite input on the PL-380). This is most likely due to the impedance mismatch between the QX output and the ferrite input on the 380.
Yes, It works fine tocouple the QX inductive via the 7.5" loopstick, but I would like to experiment a bit with disconnecting the 7.5" loopstick from the system.
