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858 ssb chassis RECEIVE MODS NEEDED !!

unit_399

EL CAPO
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Jun 17, 2008
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ALEJANDRIA, COLOMBIA SA
HELP ! HELP ! HELP !!!
As most of you know, I live in Colombia (S America). I've been CBin' for a long time, and I LIVE to talk skip. Cycle 24 is heating up, and since I am one of the few ENGLISH SPEAKING statons coming out of S. America I get a TON of responses whenever I keyup "CQ - DX ". The problem is that when the skip is "in" there is so much noise, hetrodynes, ect., that pulling anyone out of the hash and trash is practically impossible. When the skip is "in" my noise level is usually around 7 to 9 pounds !!!

What I'm looking for are mods for the 858 ssb chassis that will improve the receive. Especially the NOISE BLANKER CIRCUIT. I run a Realistic TRC-457 base. I have a 2:1 / 1:2 compander and a frequency equalizer hooked up after the volume control, and this has helped a LOT. The radio itself has a lot of mods on the transmit side but none on the receive.

I have heard people talk about using a "discriminator" to help pull weak signals out of the "mud". What is this ???????

Whatever you suggest. I will have to build it myself, so make it easy.

Thank's for the help.
 
Last edited:

there is a resistor in the ANL circuit that you can up the value on and really improve the way the ANL works.

it is R43, and it is a 680K ohm resistor.
try replacing it with a 1 Meg ohm resistor.

some people have used a 1.5M or even a 2M resistor, but i found that it started reducing receiver sensitivity and i liked the 1M ohm resistor best.

do this mod first and then check the radio, you will most likely find that it is very quiet with the ANL on, and might even make you think your receive is crippled.
you should still get an S-5 on a station that used to hit you at an S-5. etc...

you can also replace TR5 with a 2SC2999 transistor.

it is a 2SC1730 stock.

i have not done this mod myself, but i suggested it to a friend and he really thought it was a good improvement.

i think the diodes to try replacing with the schottky diodes (1N6263) are D10,11,15, and 16.

check the schematic on that one.

i think there is also a VR in this radio that can be turned up to increase receiver gain, but if its turned up too far, it generates a lot of noise.

i cant remember which one it is, but you might try checking that.

those mods and a good receive alignment are where i would start.

i would not mess with turning the NB coils in this radio unless you have all the right equip to measure them.
they will kill the receiver if improperly adjusted.

also remember that your radio is very old and the electrolytic caps might be drying out thereby creating more noise in the receive.

good luck and please post your results.
later,
LC
 
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I have done the Shottky diode/2SC2999E mod to a couple of my radios and it is an excellent mod. I liked it so much I bought 60/2SC2999E's to keep around so I can put them in all of my radios and have some left over for modifying friends radios as well. That receive kit can be founf on eBay, and there are a couple of guys that sell them. I think 'wildcat2488' -a member on this site- sells these kits as well. That is where I bought my first kit from. The Shottky diodes are a little hard to find - which is the best brand/model available for this mod - but I know 'wildcat2488' has them in his kit. It's only $4-6/US shipping incl...

I would check out all of loosecannon's suggestions, as I believe they are very good ones. You should be able to get everything like you want it with all of those tips!
 
ive tried the mods in the first PDF, and i didnt notice any difference with the transistor changes.

broadbanding L4 is a good idea if you have extra freqs in the radio.

in the second PDF, going to 2.2M ohms was too much for me, find out for yourself the value you like.

good luck in your modding,
LC
 
Loose Cannon -

Per your suggestions I spent the last 2 evenings replacing all 55 of the electrolytics in my radio, and completely realigned it. WOW !! Much lower noise and receive was a lot better. Transmit side picked up a bit too. The VR5 AM TX adjust was way off and readjusting brought the receive signals way up. Tried the 2SC2999 transistor, but didn't see much improvement. I'm going to go into Medellin this weekend and get the Shottky diodes and give them a try. The radio is already broadbanded, so didn't have to do that one.

Thanks. This was a big help. I owe you one.

Also muchas gratias to Rob and Buttfuzz.

- 399
 
not a problem 399.

glad i could help.

have you tried the R43 change yet?

this was the thing that made the biggest difference in my receive noise level in my 139xlr.

hope to make a contact someday, what freq do you call on?
LC
 
rec kit for washington 858

I did this to mine and it worked,

How to perform the 2sc2999 and Schottky diode swap for increased receive gain and less noise.

Cobra 138XLR,139XLR,Washington 858 Chip and TRC 458
D-10 change to a ecg583
D-11 change to a ecg583
D-15 change to a ecg583
D-16 change to a ecg583
TR-5 change to a 2SC2999

I also installed one of this 621 pre amps, they work also pretty good...
 
?

How did you make out.. that recieve mod is only for the first stage rec.. not the front end.. I have put it into my washington / my galaxy 959 my texas ranger 696f base, and my general grant, all worked pretty good..
 

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