Mutura filters... Hummmmmm

[Shortwave2200]

Ok, Every one on this site knows about my Aircastle Radio.

What I did not know was that they have Mutura filters installed.

Now correct me if I am wrong but back in 1969 wasn't that for only the more expensive radio's?

This Aircastle back in 1969 was 89.99. So was it considered "Low" end?

Another question, is there any way to filter out splash from close AM BC stations on shortwave? A capacitor at the antenna connection? I do not want to cut the signal just the splash from BC signals.

 

[majoco]

IMHO Murata used to make ordinary IF transformer-type and magnostrictive filters before they got into ceramics - now they seem to only make ceramics - and they are reasonably cheap compared to a crystal filter. I have ceramic filters in an old Heathkit Mohican receiver and that was late 60's.

What you are hearing is called 'sideband splatter' - more properly 'adjacent channel interference. The IF bandwidth in your receiver is not narrow enough to just pick out the signal you want without letting through the adjacent stations' sideband. You could try tuning away from the unwanted signal a bit but that's not helpful if the station you want is the meat in the sandwich! You could buy better ceramic filters and replace your old ones but you could be stepping on a minefield. The most expedient solution - buy a better receiver!

 

[mitaux8030]

Another question, is there any way to filter out splash from close AM BC stations on shortwave? A capacitor at the antenna connection? I do not want to cut the signal just the splash from BC signals.

Does that mean you're having problems with AM BC stations in the 540 to 1710 kHz intruding on other stations in the shortwave bands >2 MHz? Quite a simple solution to that: build an antenna high pass filter, with a cut-off frequency of about 2 MHz. This article discusses the theory in good detail and offers a few circuits you can build yourself; figure 3 is a good, easy to build high pass filter that will do the job:
http://www.dxing.com/tnotes/tnote06.pdf
Pre-wound fixed value off-the-shelf inductors will work just fine, its not essential to use toroid cores and wind them yourself.

Or you can buy pre-made AM BCB high pass filters ready to go.

 

[ka3jjz]

The problem of AM stations breaking through on HF is not sideband splatter, but a case of overloading.

There are several manufacturers of high pass filters that will do the job. But this will attenuate all the MW frequencies above a certain limit. For example...

SWL Filters | PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

I see that Universal Radio is selling these now

BPF-1632 Shortwave Band Pass Filter

Receive Filters, FM Notch and High Pass models

Now whether that Aircastle can handle a coax fed antenna is something I don't know.

Mike

 

[majoco]

The OP didn't mention AM BC band breaking through into SW bands, he said

splash from close AM BC stations on shortwave?

Does he mean AM BC band breakthrough, or does he man 'close' as in location to his home. I took it to mean close as in frequency.

 

[Shortwave2200]

I meant there are stations transmitting close, AM Broadcast stations, breaking through into SW bands.

Almost every AM daytime station pins my needle at night I get distant stations when the ones around me reduce their power, then I do not get bleedover on SW.

I would like to make a filter and connect it to the local side of my local/distance switch so I can still retain an unfiltered DX.

I did get this with my DX 398 but not as bad and the eton e5 as well but again not as bad.

No the Aircastle cannot accept coax, it has a Motorola scanner plug as a external antenna jack for only shortwave.

 

[ka3jjz]

Hmm...you have a number of issues here, I think, and none of them promise to have a complete solution;

a. If the RF level is so high that it breaks through your radios like that, chances are that at least some of the problem has to do with the AM stations leaking through the plastic cases and blasting full bore into your front end

b. Another possibility is that the cord to the wall wart is being coupled, and causing it to act as an antenna for the AM stations signals. You could choke that off, I think but you're still dealing with plastic cases providing little or no shielding against the RF that's already in your environment.

You could alleviate this, I think, somewhat by using a loop antenna that you can rotate and null out the offending station. I'm wondering, though, that if the signals are that strong, even a loop might not help

Sorry I couldn't think of anything more...Mike

 

[Shortwave2200]

The Aircastle has no power transformer in it anymore, I removed it DE soldered it from the main board and physically removed the transformer, so ac coupling is not an issue.

BTW it's running on new batteries installed in it 3 months ago, I run it all day and into the night, it sips power.

but anyways.... I found out that there are a lot of radio stations nearby, I live in "The Valley" in AZ, mountains all around, 360 all around.....

Could that make a difference?

 

[ka3jjz]

If those stations are all a couple of miles from you it's pretty likely your local RF environs are saturated. So yes, it's possible that what you are experiencing is all that energy coming right through the case (plastic is invisible to RF) and overloading you

Under normal conditions I'd recommend taking a portable out away from that area, but with the triple digit heat you're having now, that might just be suicidal....but it would prove the theory

Mike

 

[mitaux8030]

Well, now that you've ruled out coupling of the offending signals via the mains, next thing to try is the high pass filter trick. You mentioned it had a Motorola scanner socket for shortwave - perfect! Just get one of the AM BCB high pass filters, and use a patch cord with a Motorola plug on it. Make sure any internal antenna is disconnected, so it can only use the external antenna input via the high pass filter - and I reckon 95% of your problems should disappear. I used to live less than a mile from a 5kW AM broadcast transmitter and a high pass filter cured absolutely all my strange mixing problems on HF.

 

[ka3jjz]

That would only be a partial solution, if his RF enviornment is as polluted as the OP suggests. All the signals from the stations in the area will go right through the plastic and rubber in the portable, and get right into the radio, whether the internal antenna is disconnected or not.

Don't get me wrong, it will very likely reduce the issue, but not completely eliminate it, which I'm sure the OP was hoping...Mike

 

[ratboy]

Practically every old transistor radio I junked or fixed had murata filters in it. They aren't a mark of quality, especially the tiny ones in a lot of old stuff. Good luck on the AMBC breakthrough.

 

[Boombox]

Maybe try an antenna tuner.

 

[ka3jjz]

Again, only a partial solution due to the construction of the radios themselves. If the OP has a very high level of RF from MW stations in his area, it will go right through the plastic and into the radio, regardless of what you put on the antenna input.

Will it help? Maybe - but it won't completely cure the problem...Mike