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Schottky Receive Mod on a Galaxy 949 - Questions!

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Schottky Receive Mod on a Galaxy 949 - Questions!

Post by jwr1221 » Sunday, 28 November 2010, 12:27 PM

Hi All,

After reading Defporn's list of modifications to my 949, I decided to go for it and do the receive and noise blanker mods... (Below)
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 ECG583 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 ECG583 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.
I have the diodes on order from DigiKey... (A whopping $4.88 including shipping!)

I have also seen on other threads that these mods are tied together with swapping out the receive gain transistors (as Carl points does in this thread: viewtopic.php?t=8493" onclick="window.open(this.href);return false;).

However, I have also seen threads on other forums that caution that after these mods, a lot of radios will suffer from bleed-over...

I didn't plan on changing out the transistors because I don't want to have any bleed-over; I was only planning on swapping the diodes to improve the noise filtering...

So who all has done this mod and what kind of results did you get??? For the "cents" per diode difference, if this mod gives an improvement, why wouldn't Galaxy change the diode spec? (in other words, Galaxy probably has a reason for NOT using these particular diodes... What is it?)

Thanks for the input!!!

-JWR


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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by unit 451 » Tuesday, 30 November 2010, 7:50 AM

jwr1221

Let us know how this mod works for you. I have a DX 949 I have considered doing this mod to as well, but just haven't taken the plung yet.

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by sparky17 » Tuesday, 30 November 2010, 12:02 PM

I have an antenna at the top of a tree, and another one mounted 3 feet off the ground. The galaxy with the mod is on the antenna 3 feet off the ground, and it can hear most of the 'weak' stations that the other radio can hear with the superior antenna..

I'm on a hill, so this is kinda cheating, but I think the galaxy has pretty dang good receive..

Unfortunately I had all the receive mods done to BOTH of my galaxies at the same time, so I can't do a comparison :( .. It's been a few years since I had it done.. I can't stand listening to the static on this galaxy if it's in the base or the mobile. There's always some harsh noise, so I always have to use the squelch.. (AGC maladjustment?).

I did all my 'noise cleanup' grounding in the base and mobile after I had the radios upgraded, so I really wonder what it would sound like without the mod and if I made it more unpleasant to listen to the static by doing this..

Lower noise transistors, schottky diodes, every receive mod I could find I had done by a competent tech with proper equipment.

In the mobile I always use squelch anyways because of traffic lights, so I suppose it doesn't matter.

I haven't noticed anything I would consider 'bleed over'. Unless you're talking about bleed over from other stations? Just the standard over-mod bleedover that I get on every radio.. Perhaps I pick up traffic light noise more.. I don't think the mods would cause your TX to bleed over more...

My results are inconclusive however on the mods. I had a ton of noise prior to doing them, I still had a ton of noise afterwards. I fixed my noise problems (fluorescent lighting and car stereo) after I had the mods, so I dunno. My radios haven't blown up yet and I don't think there's any 'miracle'.. Compared to all my other base radios however the galaxy blows them out of the water on receive..

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by jwr1221 » Tuesday, 30 November 2010, 13:24 PM

Thanks for the input guys!

However, I'm waffling on whether I want to do it or not... First off, I was NOT going to swap the transistor since that will expressly void my warranty, not only with Galaxy but also with Sparky's... Second, I think I already have a "good" installation with very little "noise" (all body components, engine, battery and exhaust are bonded to frame, installed a static drain at the back and had a buddy make me a custom corona ball for my wilson trucker 2000 antenna). In other words, if I'm not picking up a lot of static or background "crap", do I really need to lower the noise floor?

So is the mod really worth it if I don't do the transistor swap? Also, I understand that replacing the transistor in TR17 improves the AM detection... TR19 (which is where you put the transistor from TR17) is the SSB detection... So does this mod improve both, or does it mainly work for AM? (With the 949, I'm interested in both!)

The last thing I want to do is void my warranty if it's not worth it!

Your thoughts?

-JWR1221

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by sparky17 » Tuesday, 30 November 2010, 13:49 PM

It should increase the sensitivity... Instead of 0.5uV maybe it'll only take 0.25uV to receive something.. Galaxy is already as good or better than other 11m radios out there on sensitivity. I think I've seen some of those fancy 'export radios' at 2uV..


Transistors amplify junk, and they have an inherent 'noise floor' within them. From my understanding, the replacement transistor has a lower inherent 'noise floor'. (I think this is part of the reason why you always hear white noise when you turn a stereo up when nothings playing.. I think mosfets are better in this regard because it's semi-isolated).

There's a noiseblanker mod and a receive mod.. I think the noiseblanker mod is all around good.. The receive mod is good if you have low noise already in your area.. If you have 7lbs of noise in your area, and your receiver doubles its sensitivity, I don't think it would make much difference, the signal to noise ratio would more or less stay the same I would think...

Wish I could give you a clear answer.. I doubt you'll notice a difference unless you do a side by side comparison with a switch. I hardly notice antenna improvements, different radios, any mods, most alignments.. Subtle changes are hard to notice.. If there's a weak station you can just barely talk to, it'd be worth a shot to do the upgrade to try it and see.. If it's just loud local stations, then I wouldn't bother unless I or someone else could confidently do it without breaking stuff in the process..

You can listen to what mine sounds like.. The frequency response is also widened (~4khz instead of 2.5khz on receive).. Live receive at my home 20. First link is audio, second link is audio and video of meter.. (This is a 979, but the insides are exactly the same)

http://24.20.127.28:8070/stream.mp3" onclick="window.open(this.href);return false;

http://24.20.127.28" onclick="window.open(this.href);return false;


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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by jwr1221 » Tuesday, 30 November 2010, 14:40 PM

Sparky,

I'll check out your links tonight; I need to shut down my computer to hop on a plane (very noisy in the airport too!) I'm assuming that I'll hear your RX; any idea on the distances to the contacts?

Last night I was on a 2 hr highway road trip and was passing a truck stop and someone comes on 19 and advertises help with antenna setup, peak-n-tunes, etc... So I hopped on and asked him out of curiosity if he did receive mods and he said "no"... He said it didn't need to be done as long as the antenna system is optimized and the radio is properly aligned... Of course, there was a charge to have him evaluate the antenna system and recommend the best one for the given installation!!!

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by sparky17 » Tuesday, 30 November 2010, 16:57 PM

jwr1221 wrote:I'm assuming that I'll hear your RX; any idea on the distances to the contacts?
That antenna is 5 feet outside the window, 3 feet off the ground (but I'm on a hill). Depends on the transmitting station. Some of them are 50 miles away. The second treetop antenna is for talking, that lower one is just for internet listening.. It probably picks up more crap from the house too..

I dunno about the truck stop repair guys.. The two local ones have horrible reputations. Kinda hit and miss I suppose. I don't take my radios to anybody that doesn't have at least the equipment listed in the service manual to perform an alignment.. Antenna tuning doesn't need any fancy equipment tho..

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by Ronin » Wednesday, 01 December 2010, 21:39 PM

My 949 is used as one of my base radios so I can't honestly say what you will see performance-wise in a mobile installation. I made the receiver mod to the 949 about 4 years ago. I made the usual tests with the locals, checked the noise floor and performed the mod. After the mod, The NB would take out about 1/2 to 1 S-unit of noise and I saw a small increase of about 1/2 S-unit on all the stations that I ran tests with before the mod. This kit was the 4x ECG583 Schottky diodes and a 2sc2999 transistor to replace the 2sc1674L original in the RF Amp. I agree with Sparky17 in that the 949 has a harsh noise floor, boh before and after the mod. Only difference is that after the mod, the noise floor did drop a bit. I was never really sure how well the mod preformed since I did not have anyway to do an A-B comparison,...until about 2 weeks ago. A good friend loaned me his DX-2547 (same PCB as the 949), and I saw first hand the difference between my 949 and his 2547.

What you are trying to improve upon by changing the RF amp transistor is an improvement in the signal to noise ratio. In comparing the 949 to the stock 2547, the receive mod in the 949 definitely had a better signal to noise ratio when switching (using a coax switch) between the two radios listening to a station that was an S-3. The same received signal on the 949 sounded louder and clearer than the stock 2547 as well. So, after that test, I decided to do the receiver mod to my Uniden Pro 810e. The 810 is an excellent SSB radio, but was always a mediocre AM radio primarily due to the constant S-1 to S-2 noise level and any signal under about an S-4 or 5 would drag quite a bit of that noise floor in with it. I performed the receive mod on the uniden a few days ago, and WOW! What an improvement! My noise floor dropped completely and the test stations came up 1 S-unit with considerably less noise on the weak signals. The NB always worked very well in the 810 to begin with, so I really don't see or notice too much improvement there, but the receiver now is fantastic. The reason I mentioned the 810 is because instead of a generic 2sc2999 transistor, I used an NTE107 which is where I am certain the very low noise floor results have come from....(as I type this, I have a zero on the meter on the 810 and an S-1 and 1/4 on the 949). My next project will be to swap the mod'ed 2999 in the 949 for an NTE107 and see if the noise floor improves.

continued................

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by Ronin » Wednesday, 01 December 2010, 22:01 PM

continued.........

On the bleed-over, I am about 3/10th of a mile (and in direct sight) of a state highway and I do not get anymore bleedover than before the mod. I usually monitor Ch. 14 here locally, so it is only the occasional driver that is running a sizable amp that I might hear very briefly. I have 2 bases about a mile away from me that both run pretty hot and I can only hear them on the adjacent channel but no further. My antenna is an Imax at 33 feet and in the clear (I am at one of the higher locations in my town), so I doubt you will see any more bleedover than what you have now even in the mobile.

I would say do the mod. It is not a very complicated mod to do yourself and does not require any re-alignment. With doing it yourself, you could always remove the mod (keep the old parts) and return it to stock if it doesn't do as well as you hope in the mobile. I would also suggest using the NTE107 transistor since the improvement was much more dramatic and obvious when I did the mod to the Uniden 810 using the NTE107. The DX-949 (and other radios using this circuit board) have plenty of strong points (functions, controls, large meter, etc.), are excellent in the transmit area, and are pretty good radios receive-wise even stock. But the mod took the pretty good receiver and made it a very good receiver, at least in my opinion. Now I am hoping that changing the RF amp transistor to an NTE107 will make it an excellent receiver like it did with the Uniden 810.

Also, I would say that there is a slight improvement in the SSB on the 949 (again as compared to the stock 2547), but I am planning on doing what you had mentioned with changing the SSB detection transistor just out of curiousity. I actually do considerably more SSB than AM.... and I am happy with the 949's receive on SSB, but,... I have to find out for myself.

Good luck!

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by Ronin » Wednesday, 01 December 2010, 22:23 PM

Oh, to answer you question..........

"For the "cents" per diode difference, if this mod gives an improvement, why wouldn't Galaxy change the diode spec? (in other words, Galaxy probably has a reason for NOT using these particular diodes... What is it?)"

Good question. In reality, it probably has to do with saving money, not on one radio, but on all the radios that that utilize that particular PCB. And, more than likely, virtually every component is within spec, but probably not the highest quality. If you produced 10,000 PCB's and saved $2 on the AM detection and NB diodes alone, imagine how much you'd save on all the diodes...capacitors...transistors.....etc, etc.

Think of it this way....If you produced a radio with the highest quality components with the tightest tolerances and only bought from the best manufacturers,........ A. the radio would be very expensive (the DX-949 would probably cost $400, and B. your customer would probably never want or need to buy another radio ever again.... you'd put yourself out of business maybe! Lol!

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by jwr1221 » Thursday, 02 December 2010, 0:26 AM

Thanks Ronin!

I read in another thread on another forum that the NTE107 is hit-or-miss from a quality standpoint and that the Sanyo 2SC2999 is a better bet??? (cpcares.com has the Sanyo's for $0.34 each and the NTE's for $1.68 each - just based on this I'm more inclined to go with the NTE...)

Is the SSB transistor (at TR19) the same 2sc1674L? (I'm assuming it is not the same; otherwise, why would you replace it?) In the original instructions, they only say to replace TR17 with the 2999... Can you just assume that if the 2999 works in place of the 1674, and the 1674 works in place of whatever is in TR19, then the 2999 will work in TR19 as well? (Sort of an if A = B and B = C then A = C thing?)

-JWR1221

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by jwr1221 » Thursday, 02 December 2010, 0:32 AM

Here's what the other thread said about the NTE107:

**the nte107 can be either hit or miss, when nte bins there parts they have a few transistors that cross over to the nte107 part (including the stock piece) so there is a very good chance you will not be receiving an upgraded part. The 2sc2999 however is an upgraded part and you should find one before using the nte107 if possible.

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by Ronin » Friday, 03 December 2010, 7:08 AM

I am not sure what the quality control issues have been with the NTE107 and I hope they have been resolved since I still have several left for preforming the receiver mods. I do plan to swap the 2999 that is currently in the 949 for an NTE107 to see if there is any noticable difference, so I will let you know what my findings are after the swap.

The mods that I had done did not referrence putting the removed 1674L into the SSB detection circuit in the 949. From my findings with the original mod on the 949, it appears that the SSB imporved slightly, and the comparison I did between the 949 and the stock 2547 seemed to show that as well. The S meter on the 2547 was very 'tight' so S meter readings were not used. I mainly went by the quality of the received signal, and the edge went to the 949. The 949 is not my primary radiio in the shack, but I may make the swap in the SSB detector in the Uniden 810 to see what if any improvement occurs.

The SSB should improve somewhat simply by replacing the RF amp (TR17 in the 949) because the RF amp is the first stage of amplification for the incoming signal and because SSB is still technically an AM signal with the carrier removed (and of course the other side band). Some radios actually list a detection component for the SSB signal and some don't. The service manual that I have for the 949 does not depict a specific detection transistor for the SSB circuit but the Uniden I have does. the detection transistor in the 810 is a 1647L stock, so I will try an NTE107 in it's place. I may do some experimenting with that after the holidays and after I get caught up on a few other projects I have been working on. If you end up doing the mod, let us know of what you find.

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Re: Schottky Receive Mod on a Galaxy 949 - DID IT!

Post by jwr1221 » Tuesday, 28 December 2010, 15:39 PM

Well, I finally did it last week! I took my 949 to work and had a couple of our Electrical engineers help me swap the transistor and the 4 diodes... (They do this sort of stuff day in and day out plus they have top-of-the-line irons to do it with!) I was sweatin' when I pulled that warranty label off, but no risk, no reward right?

End result is that the receive does seem more sensitive, and the weird thing is when there is no interference (ie: dead channel or late at night), the radio is dead silent... Freaked me out the first few times... Unfortunately I don't have any "regular" local contacts to really quantify the difference, but it does seem to be quiter and more sensitive...

I ended up ordering a "receive kit" from "**NON-SPONSOR**" for $6.50 which included the 2SC2999 and the (4) diodes... Of course, just like all the other CB shops out there, he proceeded to trash every other shop out there... Funny thing is that in an e-mail to him he confirmed that on my radio the swaps would be on TR17, D1, D2, D30 and D31 (as specified on Defpom's site and many other posts on various forums). He includes specific instructions with the kit for the Galaxy 939 / 949/ 959 and the first sentence says "Replacement parts locations: TR17, D1 D2 D21 D22." Then further down in his instructions in step #2 he says "Remove diodes D4 and D6..." What would have happened if I followed his instructions? (of course I would have needed (6) diodes to do so!

Multiple contradictions in his own instructions and yet he trashes all the other shops?? (When he found out my radio was from Sparky's, he specifically pointed out that he had a "ton" of labels from Sparky's stapled to his bench from fixing crap that they had F*&$#ed up...) In the end, the parts seemed to be correct, but I wouldn't give him any more business...

Once I get my 257 back from Magnum then it's going back in my truck and the 949 will get the switches installed for the frequency mod and then will go in the wife's van... That way I'll have a nice radio with SSB in both rides!

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Re: Schottky Receive Mod on a Galaxy 949 - DID IT!

Post by Night Crawler » Tuesday, 28 December 2010, 16:41 PM

jwr1221 wrote: Funny thing is that in an e-mail to him he confirmed that on my radio the swaps would be on TR17, D1, D2, D30 and D31 (as specified on Defpom's site and many other posts on various forums).
Those are the parts that should be changed TR17 is the receive rf amplifier D1 and D2 are the noise blanker D30 and D31 are the AM detector.
jwr1221 wrote:He includes specific instructions with the kit for the Galaxy 939 / 949/ 959 and the first sentence says "Replacement parts locations: TR17, D1 D2 D21 D22." Then further down in his instructions in step #2 he says "Remove diodes D4 and D6..." What would have happened if I followed his instructions?
D21 and D22 are 1N4148 diodes in the RX mixer circuit D4 and D6 are the same type of diode used in the IF amplifier I don't see much of a reason for changing them.
If D4 and D6 are removed without being replaced with another diode no more receive.

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Re: Schottky Receive Mod on a Galaxy 949 - Questions!

Post by Ronin » Tuesday, 28 December 2010, 18:58 PM

Glad to hear that you gained some noticable improvement after the mod. Like I had mentioned in my earlier post, IMHO, the receiver mod takes a good receiver and makes it into a very good receiver.

I have recently bought a few 2sc2999E transistors which apparently is the latest production of that transistor series. Looking at the specs, it should have even slightly more amplification as well as a slightly lower NF (noise factor). Now if I can just get caught up with a few other radio and home projects I can swap the NTE107 for the 2sc2999E and see what improvement it makes.

BTW, not surprized what you ran into with the supplier of your receive kit. Seems that alot of them do that. I myself prefer to buy a new stock radio and make the mods, adjustments and alignment myself (since I am a bit anal about everything being done to my liking), but if you can't do that, I would suggest for anyone that they make their purchases from CBRT sponsors and mention that you heard of them on the forum.


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