Re: {Collins} R-388 Spurious Response Problem



It sounds as if the signal is leaking into the first (tunable) IF, which tunes 2.5-1.5 MHz on some bands and 3.5-2.5 on others. (alternating between even and odd). If so, it would appear at 4.420, 6.420, etc. But I'm not quite sure what you mean by "center" of a band in this case.

Since there's no such thing as "infinite" feedthrough rejection, it may well be "normal", and if it still appears with all covers and shields in place, one fix would be a trap of some sort in the feedline. But first, if you're using coaxial feedline, make sure the shield is properly connected to the connector shell and is continuous throughout its length. Same with the line from the antenna tuner to the radio. Otherwise, the feedline acts like an antenna.

You don't say what kind of antenna you're using -- if you use, say, a 20 meter dipole, it'll knock the level away down, because antennas that are much smaller than 1/2 wave become very inefficient (and you want it to be inefficient at 1580 kHz).

I'd expect an antenna tuner to attenuate frequencies other than that for which it is tuned. This is definitely normal.

73
Bob

On 7/28/2010 4:31 PM, Richard Knoppow wrote:
I am getting a spur from a local broadcast station on all "even" bands with double conversion. The station is at 1580, it operates with 50KW and is only a couple of miles from here so the signal strength is enormous. I get a responce on all bands with even megahertz at the center of the band, it is in line with the 1580 position Band-2. I am trying to figure out what causes this and if its normal. The question is perhaps a bit premature because I have not done a complete alignment to the receiver, I am waiting until I can adjust the PTO range before doing that but might have a shot at it before hand if anyone thinks it would help. FWIW, the RX has a top and bottom cover but, since I've been working on it. I don't have the bottom screwed down. Another thing is that I am running the RX through an antenna tuner which is peaked at the moment on the 20 meter ham band and appears to attenuate BC stations when not tuned for low frequencies.
What goes, any ideas?


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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