I put my new dx86v in the truck and started tuning around. Now that the skip is rolling hard i noticed the adjacent chanel rejection on this thing is horrible.the receiver is so noisy and i can almost hear the next chanel clearly if a big splatter station is keying down. I dont kniw if i got a dud or. If thats how they are. On ssb it does great, on am its awful. Its the worst rxvr i have heard on a cb radio.
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Galaxy dx86v ACR is awful
- Thread starter groundwire
- Start date
Shadetree Mechanic
Delaware Base Station 808
If a big splatter station is keying down on the next channel, then he is also keying on your channel and probably ten other channels as well. Not much a receiver can do.
I realize that. When i put my 148 and a couple others in line it was a world of difference. Put the galaxy back in, nope, yuk!
Would just need a stiff alignment and if that doesn't work then it's just the way it is. I ve seen some radio the rejection are just awful no matter what you do.
If you search the forum I think there are some mods that can be done to help with that.
Maybe one of the gurus will chime in.
Sorry I'm not much help.
If you search the forum I think there are some mods that can be done to help with that.
Maybe one of the gurus will chime in.
Sorry I'm not much help.
I gave it a full alignment out of the box. Im pretty sure it is what it is. No big deal really, just a cheapie export. Lol. I pulled out another new one i have from the box and its bad too on th rx. Oh well, into the spares bin they go
Well hey?
If you want to sell them...
But before you do, look under FL3 on the Foil side - Ranger does things that I simply cannot explain...
See if they "fudged" using a resistor - in this fashion - on the foil side - the above graphic is from a 2995 SMD (695011A) - your's is Discrete - just make sure FL3 is not shorting across - it's supposed to measure open to 200KΩ Setting - output side.
The output can vary from 5KΩ to a high as 175KΩ (they use a cap)
IF it' bounces or you check the lower scale on the input side and it shows less than 10K - something is amiss.
The SSB side isn't bothered so much, but the AM side might not be broad banded enough for many users of whom are not familiar with "narrow band" receivers. So they "fudge them" with resistance ACROSS to ground, lessening the filters' "Q" (Bandwidth product) which makes more signals appear across a wider portion of the tuning in AM and FM (The FM part needs deviation so this needs to be considered) the diode RF switches then take most of the brunt of the bandwidth noise for SSB - recovers part of that "Q" factor to retrieve selectivity.
If you want to sell them...
But before you do, look under FL3 on the Foil side - Ranger does things that I simply cannot explain...
See if they "fudged" using a resistor - in this fashion - on the foil side - the above graphic is from a 2995 SMD (695011A) - your's is Discrete - just make sure FL3 is not shorting across - it's supposed to measure open to 200KΩ Setting - output side.
The output can vary from 5KΩ to a high as 175KΩ (they use a cap)
IF it' bounces or you check the lower scale on the input side and it shows less than 10K - something is amiss.
The SSB side isn't bothered so much, but the AM side might not be broad banded enough for many users of whom are not familiar with "narrow band" receivers. So they "fudge them" with resistance ACROSS to ground, lessening the filters' "Q" (Bandwidth product) which makes more signals appear across a wider portion of the tuning in AM and FM (The FM part needs deviation so this needs to be considered) the diode RF switches then take most of the brunt of the bandwidth noise for SSB - recovers part of that "Q" factor to retrieve selectivity.
Shadetree Mechanic
Delaware Base Station 808
I just pulled mine out of the truck to take a peek. I didn't see any bodged resistor on the foil side.
I think I remember LesCom putting a different filter in one of these in one of his videos.
I think I remember LesCom putting a different filter in one of these in one of his videos.
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That is part of the "cleaning" - usually these things arrive with "dead ears" requiring that "scraping" to clear out those traces - pretty sensitive area ...if not blatant..
Not all their boards used "R325" - just some of the FL3's types that they were just a little too "tight" or narrow in bandwidth - so they "fudged in a value" to leak thru signal - most of the boards never had it - but that does not mean ALL of them...
Then RCI does a cute little trick with a cap or R325 - usually a 0.5pF (even measurable?) 105 - 1MΩ to "broaden" the bandwidth - its buried under FL3 - just so the users can find stations without having to twist the clarifier knob all over the place changing their "center Slot" to the frequency counter which was like some of the others, you chased everyone around. This is a similar effect to the HR2510's RIT knob while working an older Xtal set - never the two shall meet....
If you want better results, pull those parts and Just use a Foil Shield like what was used in an older CB set in the VCO section that were found on the foil side below the sensitive areas of the VCO. These work great for FL3 and the noise factor.
Not all their boards used "R325" - just some of the FL3's types that they were just a little too "tight" or narrow in bandwidth - so they "fudged in a value" to leak thru signal - most of the boards never had it - but that does not mean ALL of them...
Then RCI does a cute little trick with a cap or R325 - usually a 0.5pF (even measurable?) 105 - 1MΩ to "broaden" the bandwidth - its buried under FL3 - just so the users can find stations without having to twist the clarifier knob all over the place changing their "center Slot" to the frequency counter which was like some of the others, you chased everyone around. This is a similar effect to the HR2510's RIT knob while working an older Xtal set - never the two shall meet....
If you want better results, pull those parts and Just use a Foil Shield like what was used in an older CB set in the VCO section that were found on the foil side below the sensitive areas of the VCO. These work great for FL3 and the noise factor.
Doesn't have to be perfect...
Same can be done for the FL3 in a 69VHP or its Base equiv or the 86V - just needs some help in keeping the free air noise out of FL3 - so it can STAY shielded.
Yeah I got mine from Lescomm and I don't remember any RX issues like this on AM. Interesting topic though, now I'm following!
73's
73's
The filter section checks out good. Now im wondering if something is a little off in one of the frequency stages during alignment. I used the galaxy dx979 service manual and it seems to be spot on as far as the radio goes. Its tx/rx is dead on, mod 100% etc, it seems to have turned out very nicely exept for the whole rx bleedover issue. But, the galaxy dx98vhp service manual also seems correct as well. What radio/service manual is best to align the dx86v? Anybody know?
Andy, have a look at this thread about that filter.
DTB "IF Filter Mod" for RCI 29xx radios?
Looking at getting a 2950DX from DTB and noticed he offers a "IF Filter mod". The website describes it as: SSB IF filter modification for RCI 2950/70DX, and RCI6900 series single-sideband radios with surface-mount (smt) circuit boards. Reduces excessive sideband receiver noise associated...
73
Jeff
Fixed one bad link ...
These are (this sites' link back at that post) where those "tricks" listed; are...one, that they do, one main one being that the removal of the WHOLE trace - which is part of an image antenna issue.
(One radiated to the other generating a weak coupling which with the IF gain as is, generates this image and noise problem.) Can't sort out all of it when there is a presence of the original IF Image; what is undesired - interacting all along the strip.
But it also confirms other problems are within this section of filtering - so the IF shield used on the bottom can provide resolution.
The other "white noise" issue is Balancing both L13 and L14 - both need not to be "peaked" but reset to prevent the overrun or literal overloading of the IF presence causing the bandwidth of IF that is expected, then the IF to be removed - when these two are "summed" at that filter - TOO MUCH IF imaging occurs, where you are flooding the Filter with the IF arriving, and the PLL's IF together - SATURATES the result and the image pulled filtered out from that - is why the noise - an ALASING (Alias) issue from extraction of signal from a heterodyned signal that was too strong on the input - generating the distortion. Or in some circles - the reflection of unwanted artifacts. (Spurries - Band Pass Filter issues) When you think of band pass, think of this as a "skirt" issue and your "skirt" is showing up in the result.
This cannot bode well for all makes and models - and also can affect mods done to increase the Hi-Fi bandwidth - which is a lot like using High Octane in an Engine not designed for it. You get great performance for a short while - but it leaves you stranded and walking back to find chump change and a payphone - kind of moment - which could have been prevented if you retune to LESSER imaging levels - kind of kills receive - yes, but you get much of your bandwidth back from the retuning and realign so its IF processing is balanced and not as strong as it was when the radio arrived with this noise problem.
This is also why I look to resistive "padding" in both Series and Parallel in using such filtering schemes.
You already know of the 10K resistor - but you also can install a resistor in SERIES to the filter can, to provide broad level reduction and can alleviate the problem using resistive padding as a means to attenuate the signal which can offer not just better IMAGE-rejection but better selectivity.
You also have to keep your ducks in a row due to ground plane images and noise that occurs. So, the Foil Shield can also provide a level of shielding rejection of noise from common mode currents and excessive switching noise occurring - but makes an effort to preserve the IF signal trying to get processed.
Many feel this is not necessary but to me, performance and Signal to Noise can be improved by simply providing any and every means possible to correctly identify and correct and even augment the issues to clear up problems others thought they were doing the right thing about which in some circles is by doing less - simplicity is the better evil than to over process the signal.
These are (this sites' link back at that post) where those "tricks" listed; are...one, that they do, one main one being that the removal of the WHOLE trace - which is part of an image antenna issue.
(One radiated to the other generating a weak coupling which with the IF gain as is, generates this image and noise problem.) Can't sort out all of it when there is a presence of the original IF Image; what is undesired - interacting all along the strip.
But it also confirms other problems are within this section of filtering - so the IF shield used on the bottom can provide resolution.
The other "white noise" issue is Balancing both L13 and L14 - both need not to be "peaked" but reset to prevent the overrun or literal overloading of the IF presence causing the bandwidth of IF that is expected, then the IF to be removed - when these two are "summed" at that filter - TOO MUCH IF imaging occurs, where you are flooding the Filter with the IF arriving, and the PLL's IF together - SATURATES the result and the image pulled filtered out from that - is why the noise - an ALASING (Alias) issue from extraction of signal from a heterodyned signal that was too strong on the input - generating the distortion. Or in some circles - the reflection of unwanted artifacts. (Spurries - Band Pass Filter issues) When you think of band pass, think of this as a "skirt" issue and your "skirt" is showing up in the result.
This cannot bode well for all makes and models - and also can affect mods done to increase the Hi-Fi bandwidth - which is a lot like using High Octane in an Engine not designed for it. You get great performance for a short while - but it leaves you stranded and walking back to find chump change and a payphone - kind of moment - which could have been prevented if you retune to LESSER imaging levels - kind of kills receive - yes, but you get much of your bandwidth back from the retuning and realign so its IF processing is balanced and not as strong as it was when the radio arrived with this noise problem.
This is also why I look to resistive "padding" in both Series and Parallel in using such filtering schemes.
You already know of the 10K resistor - but you also can install a resistor in SERIES to the filter can, to provide broad level reduction and can alleviate the problem using resistive padding as a means to attenuate the signal which can offer not just better IMAGE-rejection but better selectivity.
You also have to keep your ducks in a row due to ground plane images and noise that occurs. So, the Foil Shield can also provide a level of shielding rejection of noise from common mode currents and excessive switching noise occurring - but makes an effort to preserve the IF signal trying to get processed.
Many feel this is not necessary but to me, performance and Signal to Noise can be improved by simply providing any and every means possible to correctly identify and correct and even augment the issues to clear up problems others thought they were doing the right thing about which in some circles is by doing less - simplicity is the better evil than to over process the signal.
I will sell them if someone wants to buy them. I hate em.
Is this what you were referring to?
In the DX979 (DX86v) and all other radios derived/redesigned from the original Cobra148GTL-DX Mark 2 (PB010AB with MC145106 PLL) (1982?) - the AM(FM) RX path does not go through FL3, it goes through FL2, either a 10.695 MHz monolithic crystal filter (narrower bandwidth, looks like a crystal with 3 legs, center leg is ground), or a ceramic 10.7 MHz filter (wider bandwidth, looks like a brown 3 legged chicklet).
SSB RX (and all TX) goes through FL3, the 10.695 MHz square can 4 pole filter marked with 10M4DS or 10M04D that may or may not have the hidden surprise resistor or capacitor underneath (to lower the Q, or widen the bandwidth). But, this filter has NO effect on the AM (or AM/FM) receive section. The 4DS or 04D part of the number refers to them being 4kc wide, or +- 2kc, hence the need to offset the carrier by 2.5kc from center slot, not being 10.4 MHz. When you pass a Carrier Balanced Double Sideband signal from the balanced modulator through this, offsetting by 2.5 kc puts the suppressed carrier 500hz outside of the passband, for better carrier suppression, and the unwanted sideband signal too (even further from the center slot of the filter). So, it will pass up to 4kc of audio, from 500hz to 4.5kc.
Note where the Noise Blanker output clamping transistor is tied into, it works (so/so) in SSB modes, but not so much for AM (or AM/FM).
The reason that the Cobra 148GTL has better rejection is because the receive for both AM and SSB paths go through FT2 (FL046), the 7.8 MHz Monolithic Crystal Filter (crystal with 3 legs as mentioned above). The RX signal then splits off after FT2 and L10, in AM mode, to feed one gate of the Dual Gate MOSFET 2nd Mixer, 3SK45B. This provides better signal isolation from the 1st IF (7.8 MHz) and the injection oscillator (7.345 MHz) to get the resultant 455kc 2nd IF (AM only).
In SSB modes, the receive path goes through the 2SK19 JFET, then to FL3 (FL067), the 6 pole Crystal filter assembly. (Note: a 6 pole filter is better/sharper than a 4 pole.)
Note where the Noise Blanker output clamping transistor is tied into on the C148, it is tied directly to the input of FT2, in all modes. Also, not capacitive coupled like in the Galaxy/Ranger radios. This means it has a direct effect on impulse noises, rather than indirect by capacitive coupling.
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