Re: "Reception 2"

blueray777 <bluestarborn-/[email protected]> wrote:
Most of the frequencies that were listed as active were in the 
123.ooo mhz up to 330.000 mhz. The web page I downloaded the info 
from said to monitor these freq's in the AM band. But the little bit 
of reception I got was in Wideband. I tried all the bands, only WFM
worked. I scrolled through the squelch settings and open worked best, 
but it sounded faint and with static. But sometimes a clear
signal would come through with strength at 10 on the meter but it was 
like I said before, muffled. You could see it come in over the other 
transmission. If I set the squelch in Auto the faint signal would not 
come in, but the other would be showing signal stregnth at 10. And 
you could tell someone was talking because their wasnt any static, 
just muffled. I dont know any other way to discribe it. 
               

 

The "muffled" comms that you heard make sense if you were monitoring in WFM mode. I have accidentally switched to this mode while monitoring aircraft comms in the past, and that is exactly the reception I got - muffled, but readable signals - on the same frequency. Switching back to AM made comms sound normal again, and this should be the mode you use for just about any normal aircraft comms in the bands described on the webpage you mentioned.

I could buy the plausible explanation of the possibility of encrypted or similar radios causing your problem except for two important points: your friend with the "brand X" scanner that picked up things fine, and the fact that you were at an airshow. Airshows, especially at military bases, are are massively coordinated and rely on compatibility between ground controllers, Base Ops, maintenance and fire/rescue crews, etc. Even if they had special use radios aboard, they would be avoided during performance ops to make sure there were no miscommunications with any of those agencies. And again, I doubt the "brand x" radio had the internal setup required to monitor any "special" comms, anyway.

There are 2 more likely possibilities:

A) Your radio is defective. Take it to an airport and see if you get the same results in a place where they definitely use standard AM transmissions. Your radio's sensitivity in AM mode may have been degraded by static discharge, or the CPU may be damaged and failing to switch modes to AM even though the display says it has.

B) You were a victim of carrier blanking or front-end overload. This is a phenomenon associated with AM transmissions, where a signal loses most or all of it's strength (as received) when there is a strong carrier signal on a nearby frequency, overloading the receiver. In other words, someone with an AM Aircraft radio may have been transmitting a solid carrier signal nearby - perhaps testing the radio at a nearby hanger, re-broadcasting comms as an "open mic" for remote listening, who knows. This type of interference is easily demonstrated with a CB radio (if you have one) - have someone transmit nearby your radio on channel 10, while trying to hear a weaker station a mile away on channel 15. The more distant station will appear much weaker or even completely unreadable while the transmitter on ch10 is operating. Also, the fact that you could hear some comms in WFM may point to this situation, as the overloading carrier signal would cause no interference in that mode and you 
 would only be subject to the decreased sensitivity associated with listening to an AM transmission in WFM mode. It is still puzzling why this didn't affect your friend's "brand X" radio if this happened, but there are possibilities here too. If his radio had better adjacent channel rejection than your R2, or your R2 had a much higher sensitivity level than his radio, it would make it possible for his radio to be less affected by an off-frequency strong signal than yours. Another less likely possibility here is that you were the victim of a strong overload signal that was a harmonic generated by your IF stages in the radio. The "brand X" radio may have had different IF stage frequencies and was not affected in the aircraft bands by the same signal. If you were indeed suffering from "front end overload", it is actually possible you might have heard more transmissions by turning your attenuator ON.


If your R2 seems to pick up aircraft comms at the local airport with no problem, I'd say you may have been the victim of some kind of interference. Of course, there are other possibilities, however remote, as well. Key thing to determine is if your R2 will still pick up normal Aircraft comms - if not, you have your answer already - a damaged radio. If it does work ok, you'll probably never solve what did happen - at least not without a room full of test equipment.



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