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Sideband harmonics 7mhz away...wheres your test tone?
- Thread starter 357
- Start date
We're attacking a problem on two fronts, with only one known output.
One the radio, other? The Amp...
Output is a screen grab - showing spurs and then another with closer gapping harmonics...
Radio - we don't know - could be a customer wanting a tuneup to drive his box and there is the proof.
Amp? Already we see a input network taking in just about everything, spurs and all...
So I'm taking it in the perspective that from what I see on a scope, the only facts that fit; are a 7~8MHz spur like that is a radio that is badly in need of an alignment - or was intentionally tuned this way to boost figures.
So I know where we're all coming from on the aspects of "how did that get in there?" - only now we have a mouse in the house and Tom-Kat is working hard but still on the job of finding the elusive rodent.
I've seen amps take EVERYTHING the radio produces and barf's it right out the antenna for everyone to enjoy, including the ones that never wanted to hear it in the first place...
Sorry to be a bother...
One the radio, other? The Amp...
Output is a screen grab - showing spurs and then another with closer gapping harmonics...
Radio - we don't know - could be a customer wanting a tuneup to drive his box and there is the proof.
Amp? Already we see a input network taking in just about everything, spurs and all...
So I'm taking it in the perspective that from what I see on a scope, the only facts that fit; are a 7~8MHz spur like that is a radio that is badly in need of an alignment - or was intentionally tuned this way to boost figures.
So I know where we're all coming from on the aspects of "how did that get in there?" - only now we have a mouse in the house and Tom-Kat is working hard but still on the job of finding the elusive rodent.
I've seen amps take EVERYTHING the radio produces and barf's it right out the antenna for everyone to enjoy, including the ones that never wanted to hear it in the first place...
Sorry to be a bother...
Maybe not the 29, maybe another D-Rail radio or one of his Truck CB Sales radios. Quietly I admit to watching more than my share of his videos and I feel confident that all of his radios are “tuned” by one of those two people.
So if it’s actually the radio producing the issue at hand, then it’s one of them. I haven’t watched the video to see what radio he says is hooked to it, if he even does state which one.
Is it even possible for an amp to create such an issue, given that a purely clean radio would be hooked to it? I wouldn’t think so but I admit that I don’t know for sure, so you tell me.
Could it be his setup, for his equipment? I don’t know but I certainly wouldn’t think so. So doesn’t that put us back to the radio feeding the signal into the amp and to the test equipment?
So if it’s actually the radio producing the issue at hand, then it’s one of them. I haven’t watched the video to see what radio he says is hooked to it, if he even does state which one.
Is it even possible for an amp to create such an issue, given that a purely clean radio would be hooked to it? I wouldn’t think so but I admit that I don’t know for sure, so you tell me.
Could it be his setup, for his equipment? I don’t know but I certainly wouldn’t think so. So doesn’t that put us back to the radio feeding the signal into the amp and to the test equipment?
The video doesn't show nor give a clue - but thanks for getting back with me on this - because a CLEAN radio (read unmolested) when tested, should not produce that. (Only in the very beginning is it implied)
But a "tweaked" radio can - I've seen these results even on T-Stars - driven by dirty tuned radios. The radio is at fault - but the amp is getting the blame. Even a PC-122 can do these spurs, just not at 7~8MHz they follow the CF tuning trap crap - from a bad lattice because the TX mixer uses the "image" from the crystal filter as 1/2 the RF signal. That 10.690 - that LC mentioned. Same thing...
There are ways to get bad performance out of a Band Pass Filter sections and still "overproduce" (null effect) - most radios use two sections - but really need three to take out that "odd-N-th" harmonic - like shown in the scope snapshot. But due to the attenuation as well as total power dissipation - making up a 3-section L - there's not much left at the end for the Pre-driver to use for 440kHz of 40 channels spread. You can make the Mixer produce a little more power - but remember the outcome is what is being shown on the scope.
Remember what was once the "flagship" when Cobra sailed off to the Mainland of Malasia and produced their 148-F? Yeah, that P.O.S. - learned about the BPF response and their skirts the radio has while tracking down issues I had with the "SSB warble" - I learned a lot from that experience - but don't wish it on anyone else.
Emphasis mine.
Do you think they are clever enough to even try this?
That said, these amplifiers have the most RIDICULOUS construction methods I have ever seen. I am surprised they don't self-oscillate and explode.
Why in gods name would you work with RF and feel the need to create your own capacitors by sandwiching pieces of FR4 together?
Of course! they don't care or understand the electronics!
They have a physical issue like the transistors are not flush with the board so they build the board up with a second sliver of FR4 (they call a "pill strip") to create wonderful new capacitors all over the place.
I have to wonder if this is an artifact of this really crappy design and build system they have here.... and the amp is doing it.
LOL! Keep going - your doing fine!
(I've seen this stuff and caught h*ll for pointing it out - I'm already there with ya' I just don't want to bore everyone to death over the stuff I see - the "Creative Mind Labs " Network would be it's own satellite by now...)
(I've seen this stuff and caught h*ll for pointing it out - I'm already there with ya' I just don't want to bore everyone to death over the stuff I see - the "Creative Mind Labs " Network would be it's own satellite by now...)
Your are starting to sound like a certain someone that I was on Discord with last night.
The one that people think I am but we laugh at for being clueless
He was telling me just like you to go ahead and have all these amp assemblers taking little pieces out of me.
I think that between him and some of you that you are really having fun at my expense.
I am pretty new at this having been out of radio for a long time then getting back into it.
The one that people think I am but we laugh at for being clueless
He was telling me just like you to go ahead and have all these amp assemblers taking little pieces out of me.
I think that between him and some of you that you are really having fun at my expense.
I am pretty new at this having been out of radio for a long time then getting back into it.
If the radio is out of alignment by enough to pass the 7.8 MHz. IF, how is it still possible to produce equal spurs on each side that are about 14 MHz. apart? If the alignment is off to the high side, the upper spur should be stronger than the lower and vise versa. Bad alignment should favor one end of the bandpass or the other and not widen the bandwidth beyond 14 MHz. and perfectly equal on both sides.
For these results to happen in this stage, the tuned circuits following the mixer IC would almost have to be bypassed. That could happen if one of the caps in parallel with the inductor shorted or someone dropped a solder blob in the wrong place. Then the only attenuation these spurs would receive would be from the tuned circuits after the final transistor stage. To me this looks like the complete loss of a filter stage rather than one that is mistuned. Otherwise that balance on each side would be difficult to explain.
It's been a while since I've sat in front of a spectrum analyzer but I recall that these types of spurs can also pop up when you overdrive the analyzer. Step one was to start attenuating the input in 3db steps. If the spurs dropped out significantly more than the attenuation level, overdrive is likely occurring.
For these results to happen in this stage, the tuned circuits following the mixer IC would almost have to be bypassed. That could happen if one of the caps in parallel with the inductor shorted or someone dropped a solder blob in the wrong place. Then the only attenuation these spurs would receive would be from the tuned circuits after the final transistor stage. To me this looks like the complete loss of a filter stage rather than one that is mistuned. Otherwise that balance on each side would be difficult to explain.
It's been a while since I've sat in front of a spectrum analyzer but I recall that these types of spurs can also pop up when you overdrive the analyzer. Step one was to start attenuating the input in 3db steps. If the spurs dropped out significantly more than the attenuation level, overdrive is likely occurring.
I have one of these. If you even come close to overload the thing screeches and puts it up on the display.
He has something like -25dBm somewhere around 27.5Mhz plus 30dB of internal attenuation so it should be getting +5dBm.
It can do +30dBm but it will start screaming around 20 or so.
I don't think he is overdriving it. It may still be possible that he is but mine does not exhibit this sort of behavior.
I doubt that BBI gives a damn about what those smart people that use these things on a near daily basis on a forum say.
He is smarter. He assembles amps.
It's probably his amp
It is probably more likely that he doesn't care about harmonics at all, except for the fact that it makes his watt meter getting a higher reading regardless of its source. It's all good to him - apparently.I have one of these. If you even come close to overload the thing screeches and puts it up on the display.
He has something like -25dBm somewhere around 27.5Mhz plus 30dB of internal attenuation so it should be getting +5dBm.
It can do +30dBm but it will start screaming around 20 or so.
I don't think he is overdriving it. It may still be possible that he is but mine does not exhibit this sort of behavior.
I doubt that BBI gives a damn about what those smart people that use these things on a near daily basis on a forum say.
He is smarter. He assembles amps.
It's probably his amp
Captain Obvious here - signing out . . .
True.
MY first thought is that those other signals would not make much difference but now that I realize those are attenuated at the instrument by 30dB plus whatever external attenuation he has.. those signals could be several watts.
They are only -20dBm below the 27.5Mhz signal.
That's really not that much is it.... wow.
MY first thought is that those other signals would not make much difference but now that I realize those are attenuated at the instrument by 30dB plus whatever external attenuation he has.. those signals could be several watts.
They are only -20dBm below the 27.5Mhz signal.
That's really not that much is it.... wow.
I don't want to stir the pot here and compare one builder to another but I will say if you knew BBI, you would also know Luke does give a damn. While still in the learning process in some areas, his mind is not closed. His mind is open to technical discussion regarding things he understands and those he does not yet.
He proved this to me years ago when we had the same debate regarding single ended amplifiers versus push-pull that is taking place in another thread here. He took the time to build and measure the input and output power produced in both circuits. About a week later I received a phone call from him explaining that both the single transistor and the push-pull pair were producing nearly identical results. Don't judge the book by the cover.
He proved this to me years ago when we had the same debate regarding single ended amplifiers versus push-pull that is taking place in another thread here. He took the time to build and measure the input and output power produced in both circuits. About a week later I received a phone call from him explaining that both the single transistor and the push-pull pair were producing nearly identical results. Don't judge the book by the cover.