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A problem with these "fluorescent tube" LEDs is that the tube itself acts as an antenna and radiates. Unless the switching power supply is very well made, which is not very common,? its pulses are very steep and not controlled and so they produce interference that is radiated and conducted. The conducted one can be stopped with the ferrites at the input but the radiated one is quite difficult to eliminate, you need to filter the power supply output to the LEDS. The solution could be to change the power supply (not always possible) or changing the whole fixture.

Regards,

Ignacio EB4APL


El 23/06/2021 a las 1:23, JonI via groups.io escribió:

Tony's revamping of the HF to LF SDR, and its arrival today, caused me to further track down interference since it was worse on LF.? I've managed to find and eliminate almost all such sources now with one exception:? I run an LED "fluorescent" light in the kitchen.? It's a small unit with obvious switching power supply within. Unfortunately, it causes interference around 4 Mhz.? A trick I tried with my cordless phone base, also causing interference, and that trick was wrapping the power supply wires through a couple of ferrite cores, is not working with the LED fluorescent.? It continues to cause a buzz in HF.? It's a safety hazard to one of the occupants living here not to have the light plugged in 24/7, so I would appreciate any suggestions you might have.

Thanks!

Jon

Tony's revamping of the HF to LF SDR, and its arrival today, caused me to further track down interference since it was worse on LF.? I've managed to find and eliminate almost all such sources now with one exception:? I run an LED "fluorescent" light in the kitchen.? It's a small unit with obvious switching power supply within. Unfortunately, it causes interference around 4 Mhz.? A trick I tried with my cordless phone base, also causing interference, and that trick was wrapping the power supply wires through a couple of ferrite cores, is not working with the LED fluorescent.? It continues to cause a buzz in HF.? It's a safety hazard to one of the occupants living here not to have the light plugged in 24/7, so I would appreciate any suggestions you might have.

Thanks!

Jon

Maybe I never noticed this before, but during my tuning around with the SDR, I notice an apparent communication mode and I'd like to find out what it's called.? I hear it on the lower part of the bands, not up where voice is.? If I listen to it on USB, for example, it is a series of closely spaced tones and they almost have a musical quality.? It must be communication because one series will stop and then another will start, but the tones will be slightly different.? Can someone tell me what this is called?? Thanks!

Olivia possibly. If you do a search, there is a website that will help you ID various modes. Also Ham Radio Deluxe will auto detect most digital modes.

On Jun 21, 2021, at 10:21 AM, JonI via groups.io <ji425bt@...> wrote:


Maybe I never noticed this before, but during my tuning around with the SDR, I notice an apparent communication mode and I'd like to find out what it's called. I hear it on the lower part of the bands, not up where voice is. If I listen to it on USB, for example, it is a series of closely spaced tones and they almost have a musical quality. It must be communication because one series will stop and then another will start, but the tones will be slightly different. Can someone tell me what this is called? Thanks!

On Jun 21, 2021, at 10:21 AM, JonI via groups.io <ji425bt@...> wrote:


Maybe I never noticed this before, but during my tuning around with the SDR, I notice an apparent communication mode and I'd like to find out what it's called. I hear it on the lower part of the bands, not up where voice is. If I listen to it on USB, for example, it is a series of closely spaced tones and they almost have a musical quality. It must be communication because one series will stop and then another will start, but the tones will be slightly different. Can someone tell me what this is called? Thanks!

On 19/06/2021 12:40, JonI via groups.io wrote:

As you know, made the 9:1 unun yesterday for the random wire and it is performing fabulously well!

Jon

do you mean a turns ratio of 9:1 or an impedance ratio of 9:1 i.e. a turns ratio of 3:1?

73
Nick

Jon

To be honest, I don't see any significant difference between the two plots. Through 30 MHz generally, and certainly below 10 MHz, the absolute strength of the received signal has no importance whatsoever for reception quality. What determines the received signal readability is the signal to noise ratio.

A preamp, in most cases, makes no difference either. A preamp increases the signal and the noise together and does nothing to improve signal to noise. It may, in fact, reduce signal to noise because it is one more gain stage that is susceptible to overload and intermodulation.

If the noise level in your receiver increases when you attach the antenna then there is nothing your can do at the receive side to improve signal to noise.

If you feel better about it then by all means use it. Just understand that relative signal level in and of itself is immaterial. The only thing that matters is signal to noise.

WA8TOD

I guess I do not understand the rationale for a 9:1 unun. The implication is that the random wire has an impedance of 450 ohms. There probably IS a frequency at which the wire has an impedance of 450 ohms but to hit that frequency by chance would be highly improbable and it certainly would not present that impedance over a range of frequencies.

A random wire has two very predictable impedances: nominally 50 ohms at frequencies where the length of the wire is an odd multiple of a quarter wave and nominally 2600 ohms where the wire is an odd multiple of a half wave. At all frequencies in between the wire represents a random impedance between a few ohms and 2600 ohms.

The fairy tale that a 9:1 or a 49:1 balun that makes a random wire into an efficient broadband antenna is simply wrong.

I know, I know...... your SWR bridge says you have a 2:1 or better VSWR over a broad range of frequencies. The reason for that is the 9:1 balun is relatively efficient at the frequency, if there is one, where the wire represents a 450 ohm load. But the balun is wildly inefficient at all other frequencies where it is badly mismatch and the majority of your transmit power on those frequencies is turned into heat in the balun. The reason your SWR bridge shows a low number is it is measuring reflected power and any loss between the transmitter and the load represents a double loss, once for the outbound power and a second time for the reflected or return power. Your SWR bridge sees low reflected power because it is mostly lost in the balun. In most cases less than 50 percent of your power actually gets to the wire and in many cases it is less than 10%.

The principle is exactly the same for the famous EFHW antenna fed by a 49:1 transformer. This antenna is an excellent, efficient radiator at the frequency where the wire represents EXACTLY an odd multiple of a half wave. At that frequency the wire presents a nominal 2600-3000 ohm load to the transformer. The transformer efficiently converts that impedance to something close to 50 ohms (2600/50=52 ohms) and you will get a low VSWR and an efficient antenna.

At all other frequencies the transformer sees a horrible mismatch because the wire presents nothing close to the necessary 2600 ohms. So the transformer delivers whatever power the mismatched wire will take and converts the rest to heat. Reflected power is low because it suffers a double loss in the transformer. So your VSWR bridge tells you your magic transformer has violated the laws of physics and turned a random wire into a constant impedance load across a broad range of frequencies. It is lying and there is no such magic transformer. And you are getting very little power to the wire on the vast majority of frequencies.

I realize this is heresy to the "EFHW" advocates. "I make contacts on different bands all over the world with my EFHW". Well, if you start out with 100 watts and you end up with 10 watts or less at the antenna you have suffered a 10 dB loss, and you will on most frequencies where you use such a contraption, then 10 watts can make contacts all over the world. I regularly make contacts into Australia and New Zealand on 100 milliwatts. But those who think it is a magically efficient broadband antenna are just fooling themselves. Or, more accurately, are being misled by their SWR meter into thinking that is what they have.

WA8TOD

OK - now it works a little. I indulged in a Startech USB audio card - the kind about the size of a pack of cigarettes, bristling with buttons & connectors, and definitely having a stereo line input. I was able to do the calibration of the LO and also the phase and amplitude of the two baseband signals.

Now I can hear my tinySA set at -60dBm. And it receives WWV. Weakly. And I have heard a few CW signals.
No SSB yet...

I figured out how to enable transmit from HDSDR - after many warnings about how I shouldn't do it without a ham
license :).

Haven't succeeded in making any RF though.... Probably something to do with the setup of the sound card.

As you know, made the 9:1 unun yesterday for the random wire and it is performing fabulously well!? Gave the wire new life.? Now the big question is how to weatherproof it as it will be outside all the time? The way I made it was placing the toroid into a homemade box.? The box I made yesterday from pieces of copper clad circuit board.? I tack soldered the sides but, as I made the whole thing on the spur of the moment, there is much uneveness of sides and I didn't want to use my roll of solder on all of the seams.? I was thinking of following up with something like outdoor silicone.? I also have liquid electrical tape handy, but it would be more awkward to fill the gaps than with the silicone/ caulking gun.
Your thoughts welcome and thanks in advance.
Jon