I'm trying to figure out if I have various types of radio overload correctly defined, or what certain types are.
I've heard/seen references to "front-end overload". As I understand it, that would be when your receiver begins to desense/block (i.e. a station is not heard that would be heard if the strong signal wasn't on the air, even if no audio from the strong signal is detectable), or a station is being heard on frequencies it doesn't belong.
As I understand it, examples of the 2nd category would be a station showing up 900 kHz below its assigned frequency (on a radio with a single conversion 450 kHz IF), a harmonic (for example 760 showing up on 1520), an intermod mix (several years ago in my dad's mid 70s pickup that radio heard 600 and 1130 mixed on 530), or modulation splatter or IBOC hash spilling over onto the adjacents (for example tuning to 1180 or 1160 and hearing splatter from a station on 1170). Am I understanding that correctly?
However, when I tune to the offending stations' actual frequencies, the audio, in most cases, is clean, unless the signal is extremely strong.
I had always (or previously) thought that "overload" meant the station was actually distorting / compressing / clipping /etc, on its own frequency.
So, apparently just having splatter, blocking/desense, intermod, harmonics, IF images, etc, is called "front-end overload".
This 36-second clip is what I've thought overload was...760 KFMB - Tecsun PL-606, adding Select-A-Tenna & groundwire (on utility pole) partway through
The signal is relatively clean for about the first 20 seconds or so, after which I slowly move the PL-606 closer to the inductively coupled dual antennas over the next several seconds, until the PL-606 is resting on the Select-A-Tenna (which in turn is being held up to the utility pole's grounding wire) for the final several seconds or so. BTW I'm about 7.3 miles southeast of their 50kW transmitter.
So what would be the term for describing that type of overload, if "front-end" is for the less severe type? I'd like to be able to refer to one or the other (or other types of overload) using a couple words, without having to take an entire paragraph to describe what I mean.
Also sometime several months ago I had the Tecsun PL-380 (same DSP chip, smaller antenna so not quite as sensitive) and Select-A-Tenna outside the antenna farm for 5kW 910 KECR and 50kW 1170 KCBQ, doing the same experiment.
Normally, with those DSP radios (PL-380 and PL-606), when you first turn the radio on, or access certain functions, the audio is usually muted briefly (anywhere from maybe a second when changing a function (although just tuning up/down on the same band only mutes for a small fraction of a second, if that) to several seconds when turning the radio on or off).
However, when I had the PL-380 and SAT up to the groundwire with the SAT tuned to 1170, I could hear distorted audio from 1170 KCBQ at ALL times, from the instant I hit the power button to turn the radio on (bypassing the usual several second delay), through changing bands/functions/etc, even to turning the radio off (the audio wouldn't disappear until the display had changed to showing the clock, AFTER it said "Off")!Here's an audio clip.
The signal was so strong at that location
that its harmonics were showing up
near the FM band
, and was even overloading a crystal set
that otherwise only had a small ferrite bar
for an antenna.
That happened at a signal strength well above that at which the previous overload demo clip was exceeded. (With that previous one, a stronger signal would have less audio come through until it eventually would sound like an unmodulated carrier.)
What's happening when I have that more severe example of overload?
(Also sometime I'll want help figuring out how to calculate the gain I'm getting from those big wires that seem to be acting as antennas, but I'll save that for another topic some other time.)