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Message |
    
Flush
Junior Member
Username: Flush
Post Number: 20
Registered: 11-2006
| | Posted on Thursday, February 15, 2007 - 12:13 pm: | 
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Is there a way to remove the background noise on the receive of distant stations? I have a noise canceling ext speaker that does "ok" however some kind of added noise blocker would be nice.
I did the diode ears mod on the 949 and cant realy tell the differance(have a 949 & 959)
The galaxy noise filter or GNF is useless as it just muffles and changes the tone to make the distant stations even more unreadable. I get best results with the tone on med or low and the NB/ANL switched on. With a preamp it only amplifies the static.
Can this radio be made to receive or do I need to go to the piggy bank again  ?
Aloha |
Caledonia
Member
Username: Caledonia
Post Number: 55
Registered: 8-2005
| | Posted on Thursday, February 15, 2007 - 2:43 pm: |
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An audio filter would do what you are wanting. I think MFJ makes one that is reasonable.
Bruce would be the guy to ask. |
Flush
Junior Member
Username: Flush
Post Number: 21
Registered: 11-2006
| | Posted on Thursday, February 15, 2007 - 4:16 pm: |
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Any more info on this filter? Is it a circuit that is installed on rx side? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2393
Registered: 9-2004
| | Posted on Thursday, February 15, 2007 - 4:57 pm: |
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these are all good upgrades for your radios, and are highly recommended.
the one mod that will make the biggest difference, and if you do nothing else; do this mod, is the TR17 change to a 2SC2999 transistor. the stock one is a 2SC1674 and has a higher noise figure.
by replacing it you will increase your signal to noise ratio by about 6db.
seriously, you will notice the difference after doing this one mod. you must re-tune the receiver coils next to the TR afterwards.
you can get them on the auction site.
AGC (Automatic Gain Control) Improvement
Like the EPT690010Z, the automatic Gain Control response is controlled via resistor R42 (100K). If you find that your local buddies sound "garbled" on SSB, you can remedy this by changing R42 to anywhere between a 33K to a 56K resistor. All radios seem to respond differently depending on the value used. You may have to experiment with different values within this range. Like the EPT690010Z, you can make the AGC variable by installing a 100K potentiometer.
Power Amp Improvement (2SB754) - Q54
This is the best improvement you can make to this chassis. The stock device is a 2SB754, which is a 60-watt, 7A power amp device. This does fine for stock radios. However, in order to stabilize the voltage on the board after improving the RF output and boosting the modulation, the 2SB817 becomes the better choice. The 2SB817 is a 100-watt, 12A device which allows greater voltage stability for the entire radio as a whole. I ran my test DX959 with the stock device and noticed quite a bit of wobble and light dimming. After replacement, the radio responded with almost no blinking, zero wobble and a healthy increase in RF output as well as swing. Replacing this device also allows you to increase the input voltage to 14.5VDC, provided you also replace all the 10V caps in this section of the board to 16V ones.
AM AF Amplifier Improvement - Q55
This is another improvement, which has previously been published for the EPT690010Z. The stock AF Amplifier is the 2SA473. Replacing this with the 2SA1012-0 or the ECG153 will improve the clarity and volume of the modulation. It will also run much cooler which provides stability for the device. If you plan to use the DX959 or DX949 with the provided stock microphone, this upgrade is highly suggested for maximum AM modulation.
Receive Improvement - D30 & D31
The stock AM Detection diodes are 1N60P devices. These are adequate but can be greatly improved by replacing them with the 1N6263 or NTE583 Schottky devices. The replacement diodes allow greater copy of distant stations without allowing your local buddies to overdrive your radio. I have obtained a gain increase of approximately 3db on stations more than 20 Miles away. This modification is especially noticeable in mobile installations where you are forced to use an inferior antenna system (as compared to a base station setup).
Noise Blanker Improvement - D1 & D2
The Noise Blanker diodes can also be replaced with the 1N6263 or NTE583 Schottky devices. The improvement over the stock diodes can be rather dramatic, depending on how noisy the environment is around the operating location. Again, this modification is most noticeable in radios being used in mobile installations. |
Caledonia
Member
Username: Caledonia
Post Number: 56
Registered: 8-2005
| | Posted on Thursday, February 15, 2007 - 7:59 pm: |
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An audio filter is usually an external box that connects between the radio and an external speaker.
They have adjustment knobs that you fiddle with until everything is gone except the signal you are trying to copy.
One of our local ham club stations used to have one (they may still, it's been awhile since I was there) and it was very effective. |
Chad
Senior Member
Username: Chad
Post Number: 1282
Registered: 11-2004
| | Posted on Thursday, February 15, 2007 - 11:34 pm: |
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I did the "TR17" mod and the "noise blanker" mod on my 2547 and it helped a bunch.
And that's all I'm gonna say.... PAT!
Chad
CEF 433
HAM 212
not an ego thing, just keepin' the mods happy 
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Hotwire
Senior Member
Username: Hotwire
Post Number: 2180
Registered: 1-2005
| | Posted on Tuesday, February 20, 2007 - 8:27 am: |
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Flush, What is the source of the noise that is bugging you? Is it just normal background noise? Static from the atmosphere is normal. A radio with a good sensitive receiver is gonna do that. That distant station is just not strong enough to cover it up.
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
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Flush
Junior Member
Username: Flush
Post Number: 23
Registered: 11-2006
| | Posted on Tuesday, February 20, 2007 - 4:14 pm: |
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Yes it is that atmosphere static. If I set the tone on low and use a noise canceling ext speaker it helps but still have dificulty hearing. Sometimes it seems as if others are ghost talking but I can hear something talking back.. Have no problem w/ssb.
On a side note.. A few days ago we were picking up Japan like crazy. I was unable to make a contact due to the langauge. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2183
Registered: 1-2005
| | Posted on Monday, February 26, 2007 - 12:35 pm: |
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Flush, Is this a base or mobile setup? Are you using fresh coax with good connections. Living around the ocean it would not take long at all for a base antennas coax connections to corrode or just get all funky inside due to water and salt. Starts on the inside of the pl-259 and makes its way down the inside of the coax jacket. If your setup is mobile or base regardless of how new your coax is give it all a good inspection. Won't take long for salt water to do damage to copper and pl-259 connectors!
This could be causing your static or just making static worse.
Also if your radio is working well SSB should be less noisy.
Hope I could help.
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
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Hotwire
Senior Member
Username: Hotwire
Post Number: 2184
Registered: 1-2005
| | Posted on Monday, February 26, 2007 - 12:51 pm: |
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Most of the time very annoying cb problems are solved by the most simple solutions that we overlook every time.
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
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