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Author Topic:  (Read 4516 times)
EHAMFUN
Member

Posts: 3




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« on: August 08, 2002, 04:32:46 PM »

This is my problem. If some station broadcasting at 8.125 Mhz, (one of the intermediate freq.) I hear them in all bands and all freq. I turn the main dial and this signal stay on background all times. I don't have poor reception but this signal in clear freq. it's about 1-2 units. I'm trying everything with no luck. Reset, full reset, hard reset. Any comment or suggestion appreciates.
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N2MG
Administrator

Posts: 10046



« Reply #1 on: August 08, 2002, 06:42:54 PM »

Have you tried any front-end attenuation? Sounds like a close-by transmitter overloading something - and the problem may not be in the radio...
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KG6AMW
Member

Posts: 628




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« Reply #2 on: August 09, 2002, 07:21:00 AM »

Really hard to tell for many of us who have no training in electronics repair. Selectivity is one issue, but the fact that it occurs at 8.215Mhz tells me you have perhaps a leakage problem in the second coversion stage that gets carried throughout the bands.  Sounds like a trip to the service department is in order.  
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K5DVW
Member

Posts: 2193




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« Reply #3 on: August 09, 2002, 07:32:14 AM »

Since you mention this is on your IF frequency, unfortuantely you may be stuck with it depending on where the 8 Mhz transmitter is located and how strong it is.  

Sounds like a case of leakage into your IF stage. It depends on where the leakage path is as to how to fix it. If it's thru the antenna connector, you might get lucky with a front end notch filter at 8Mhz. I think this would be the case if the 8 Mhz transmitter is far away from you.

If it's coming into the radio's IF stage, unless you mess around with the sheilding inside the radio or relocate the radio where the signal isnt as strong, you're not likely to fix the problem. This would be the case if the 8 Mhz transmitter is somewhere real close to you.
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K3YD
Member

Posts: 55




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« Reply #4 on: August 09, 2002, 12:20:40 PM »

I'd try a tuned notch filter on the back of the radio.  If that helps, but doesn't eliminate the problem, I'd add a tuned coax stub.  Between those 2 you should get about 90 dB of attenuation.  Good grounding of the radio may be essential, or may contribute to the problem--try it both ways.
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EHAMFUN
Member

Posts: 3




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« Reply #5 on: August 09, 2002, 12:32:17 PM »

Thank you all for response. It's not hard to explain how I discover that problem. I try with little more details. I search the freq. starts from 40 meters band (7.045,00). IPO ON and ATT -6 db. The propagation it is low and I hearing something like station out of freq. together with the usual receiver noise S 2-3. I'm trying to tune on this station on LSB, with up and down tuning but no luck. I try next on USB with same results. This is strange, I think on this time. Any way I try all possible position of receiver. IPO, ATT, also the two different preamplifiers of FT-920. I give something up us a bad job after few minutes because nothing happened. I don't manage to clear this broadcasting. Next I go to 20 meters band. Oh my god.  IT'S SIX OF ONE AND HALF A DOZEN OF THE OTHER. Every freq to tune the same things happened. After lot checks I fund that happened up to 4 mhz and low to 21 mhz. In all that area and in every steep I was hearing that out of tune (demodulation) station. I spend lot of time to thought about this and at final I think to check that 8. 215 MHz intermediate freq. BINGO MAMA! There it's a something like Arabs station to talk on USB bring here in Greece S 6 to 7. I put the one vfo there and with other I search up and down. When this station talks I have all that reflections. When stop to transmits stops that reflection. To top it all today I receive from INRAD one 1.8 crystal filter. I open the case of FT-920 and I change the OEM with this new one. After those changes I still have the radio upside down I turn it on and I'm think to check one more time for this problem because I have front of me all that choke coils and resistors trimmers. If I touch it for some extra grounding I think may be have some positive results. I forget to write on 8.215 MHz the receiver has a whistling. I turn the vfo on 8.215 Mhz and start with a cable to connect one by one the metal cases of coils with chassis. Accidentally I touch a small coaxial cable and my GOSH !!!! the level of the whistling going 80% down. That's it. That coaxial have on the ends, in solder position, not well ground. The metal ends perhaps have some copper corrosion. If I move it a few centimeters the noise come high and low. I fix it with extra soldering and I make a hard test. I transmit with another radio on 8.215 MHz USB on dummy load 100 Watts side by side the radios and before that mode with power gain to zero on my second radio (FT-890) I have S3-4 on FT-920 in all bands idols, now with full power 100 watts and open thru all attenuators on FT-920 just I hear with volume to full more down of whisper a idol. I think my problem solved. Thanks to N2MG, KG6AMW, K5DVW for response with usefully infos and all those reads this article. Thanks on last time before post to K3WD for that also usefully info.

Best 73
Chris    
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