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Spurs - BPF fix?
#ubitx
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There seems to be a consensus from all the many posts on spurs, (not harmonics)? that a BPF following the Mixer and into the PA driver stages is required.
From what i can glean, only the bands above 20M will require such filters.? As Allison has alluded to in a few posts, it's relatively easy to do on 10M as the spur is some distance away. Not so easy on the others. If this is the way to go, then we should come up with designs for such filters. Those that are skilled in this area can obviously contribute. If indeed it is practical then my thoughts are to mount a small pcb vertically in the area of the existing 30MHz LPF. For control of the filters, a simple method appears to be the use of the SN74CBT3253 multiplexer chip as used in mcHF BPF switching.?? To control the chip requires 2 bits and give 4 possible filters. (enough ?) ? To actually provide these two switch logic signals, my proposal is to use an I2C expander chip, the PCA9536D with suitable firmware changes.. The picture shows a PCB with 4 BPF on it just to show how it could be done. NOT ones for uBITX I should add. It's about 1" high and has smd parts on it.? The filters below 10M band though will require fairly hi-Q inductors i think for good performance. Tuning the filter could be an issue if you don't have an SA.? The filters may tend to be a bit lossy, so a buffer stage might be needed also. glenn - vk3pe vk3pe |
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Glen,
I tried this and it does work... Copy the output low pass filters as they work in the slot (currently filled with the 30mhz low pass) before the power amp.? I removed that filter and inserted the switched with relays(2 per filter) 4 filters 3 identical to the output filters as low pass and the 10M slot was a band pass Parallel, LC series LC, Parallel LC, configuration using toroids as wide band pass for 27.4 to 30 mhz. This worked well and the receiver worked better with less out of band spurs. The low pass can be with commercial coild like those from coilcraft and MLCC caps as they do not have to be tuned.? The band pass is wide enough that with decent parts? (out of the bin ceramic caps and toroids wound and check for inductance) it just worked without tuning.? ? Using SMT coild the size would be very small. However the relays are bulky and I didn't try diode switching. To control the added relays:? I'd already modded the TX-A/B/C down to two lines so TX-A was available I used that and a 4bit latch (74LS75) to grab data from the 4 LCD data lines when the LCD is not being updated.? The code mods were trivial and all in the?setTXFilters? routine. An easy 4 bits of output to control 4 relays. It also lowered the output of harmonics as well for CW for 80 and 40. Allison |
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Hi Glenn,
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Just a slight correction. Allison said it's the bands above 17 meters. You left that one out. I Made note of that because I use that band. I am using mine on the bands from 80 through 17 meters with external low pass filters to reduce harmonic content. Just until a fix that I like comes along. In addition I use my uBitx as a bench tool working on other radios. In signal generator mode the finals are disabled and no signals sent to the antenna. It's much nicer using the uBitx for this in place of a whopping big tube radio! 73, Bill KU8H On 08/10/2018 12:14 AM, Glenn wrote:
There seems to be a consensus from all the many posts on spurs, (not --
bark less - wag more |
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I assume this doesn't quite work for the spurs at 15m and above in SSB mode.
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A fix for that would involve adjusting mixer LO levels, getting consistent gain on the 45mhz IF, and cleaning up the gain distribution between mike and the first mixer at T2. And/or moving up from 45mhz to something beyond 70mhz. On Fri, Aug 10, 2018 at 07:25 AM, ajparent1/KB1GMX wrote:
Copy the output low pass filters as they work in the slot (currently filled with the |
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Well, the per-band BPF would work at 10m, but perhaps not on 15m and 12m
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where the spur is too close to the operating frequency. On Fri, Aug 10, 2018 at 07:48 AM, Jerry Gaffke wrote: I assume this doesn't quite work for the spurs at 15m and above in SSB mode. |
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Allison, your Argo 505 post reminded me that the 505 peaked both the RX and the TX-driver, but my 509 peaks only the RX. ?This may well explain why the 505 is so clean. ?So, instead of the 30 MHz LPF why not use a peaked filter tuned to the operating frequency, with a manual adjustment on the front panel, or maybe put a tunable filter in series with the LPF.
You are always several steps ahead of everyone, so perhaps you have already tried this? 73, Tom ?W1EAT |
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Allison Hmmm.......your post stimulated thoughts about possibly stripping, or just disconnecting, existing output filter components and adding a jack for each end of individual BPF as plug-in solutions until something better is devised.? Most could live with plug-in ham-band BPF as an interim solution.? Test points on the uBITX board might be the place to put the BPF jacks. T-37 toroid cores are inexpensive and are said to handle up to 10 watts.? Quality capacitors are inexpensive and readily available.? A full set of individual band filters should cost less than US$30...less if you only need a few bands. Problem with this idea is if you want to use the uBITX as a general coverage receiver, or want to transmit on non-ham frequencies, you would need filters for the frequency range involved. This does not fix the garbage-in problem with input to the IRF510s, but it does allow treating its symptoms.? Arv _._ On Fri, Aug 10, 2018 at 8:25 AM ajparent1/KB1GMX <kb1gmx@...> wrote: Glen, |
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Arv,
If you strip the filters as is and use them externally as an inline element they perform perfectly. The torids used are adequate to 10W, maybe more with a good SWR.? For those running more power or maxed out you need a bigger filter components. Like I proposed earlier in this one in? #56618... IF you take out the 30mhz (actually 33mhz) low pass that 9element one and replace it with three of the filters used at the output and one band pass for say 10m you will get 3-near 20mhz coverage with no issue RX and clean up the TX and 10M becomes usable. and the CW harmonics are lower as well. Its three low pass filters (no tune), and one wide bandpass for 10M. Allison |
开云体育All:
Have you considered changing the LPF L1 to L4 with a bandpass filter that is tuned for the operating band? That should help both harmonics and spurs and improve receive performance as well. Howard On 8/10/2018 1:31 PM, ajparent1/KB1GMX wrote: Arv,
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Tom,
Not an aha!? No one I am aware of those the ubtix approach for wide open as spurs are the primary issue.? The usual DC to daylight uses a mix of high pass, wide bandpass and low pass to contain the unwanted. Tentec was clever but not stupid.? Leaving out the pre-selection on TX was simpler as the band switch selects band pass filters so the user cannot tune the TX out of band.? HINT: it was done to insure CB was not possible without digging deeper inside.? The 505 it was a VFO tweak only.? For the 509 and others it was VFO change and retune (and add caps) to the band pass filter and also changing crystals. The difference is the 505 tunes both. its a mechanical nightmare but? works well if wear has not damaged it.? But you must dial up the preselector to even transmit and it can be out of band... oops!? It also means tune up before you can transmit at all. ?The 509/540 use band pass filters for TX and not low pass filters at that point and tunable pre-select for RX. They have to switch between the RX path and the TX path for all the 505, 509 and 540.? The TX filters are switched by the band switch.? A 509/540 really will not work for TX out of band because of that.? The tunable pre-selector on RX allows for things like out of ham band RX using the VFO images (in the users manual). Its actually very clean both ways. They were built to the common industry standard of the day that being? Carrier not less than -60dbc and harmonics and spurs not less than -60dbc.? The same idea can be applied for the uBitx either a tunable? pre-selector or wide band RX and a relay switching in the band pass filters for TX. For those of us around long enough in industry the -43dbc was to tighten low? spec stuff, home brew,? and loosened high end.? Only for ham gear.? It did however make it more uniform. Allison |
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On 15m and 17m, it would take a very fancy bandpass filter to take out the spur. The spur is too close to the operating freq. Example for 15m:? ?When operating at 21.45mhz, spur is at 45-21.45 = 23.55 mhz On Fri, Aug 10, 2018 at 10:46 AM, Howard Fidel wrote:
Have you considered changing the LPF L1 to L4 with a bandpass filter that is tuned for the operating band? That should help both harmonics and spurs and improve receive performance as well. |
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Jerry,
Not a fancy one, a well developed one without compromise.? its pretty much specific to 15M.? However we only have to knock it down not eliminate it. Since the worst I'd seen was -25dbc if we can achieve 20db of attenuation at 23.55mhz and up?we have a win.? Remember the spur goes down as the frequency goes up. For 12M the spur is at roughly 20mhz so a bandpass can work and not be complex one. A really good high pass will allow 12 and 10M. as the spurs for those are 20mhz and below. For 17M the spur is at 27mhz.? so a good low pass at 19mhz will do, that's the 20M filter. When its working. As I said at the outset more than a month ago.? its 20mhz and up for the spur. and the only reason it gets out is for 20mhz and up a low pass filter is lets everything below out, as it should.? The scheme for the radio works, mostly.? The identified cases are pretty much unique and well identified.? Also the amount of rejection needed is very manageable.? Its just a simple single 33mhz (actual design frequency as best I can tell) low pass cannot do anything for the spurs. So three low pass and one high pass gets up 80-17 a transmit only gap and 12-10 not bad at all.? With five filters we have 80 through 10.? How to integrate that is a different issue but a simple board with relays or (diodes) to select them is a viable solution.? ? ?At the same time it lowers the demands for the output filters which we know work except for board level issues do not perform as well as needed. The output only needs the existing four filters only with better switching (more relays).? Since we are power limited smaller relays can be used as they can be had in about half the size of the existing ones and small cost.? I say that as I see proposals for lots of filters and all when not needed. Do both and most of the big ugly issues are done. Allison |
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At 21Mhz I guess is very hard to take the spurs out unless via a tunable notch. Il 10/ago/2018 21:59, "Jerry Gaffke via Groups.Io" <jgaffke=[email protected]> ha scritto:
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开云体育Can we change CLK#1 to 66 MHz? Then the
spur should disappear? Or is it 66 MHz already?
On 8/10/2018 4:53 PM, iz oos wrote:
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why 66mhz?
CLK-0 is the bfo and clk-1 is the second conversion so its either roughly 45+12=57mhz or 45-12mhz=33mhz in round number the actual are about 15-20khz from those. IF clk-1 were 66 45-66=21mhz or maybe 111mhz either are not the first IF, no RX no TX.? We have? dual conversion with 45mhz fixed IF,? then down to? 12mhz , unlike the base Bitx(20/40/17) which is single conversion. The way we tune is CLK-2 is 45mhz higher than the desired frequency or 48 to 75mhz to cover 3 to 30mhz RX/TX.? So at 21mhz the CLK-2 is? 45+21=66mhz.? ? We can try...? If we use 45-21=24mhz for clk-2... except 24mhz will leak out, 21mhz, and 3mhz. (mix of 24 and 21 also others we do not want).? That would not work well at all Mixers are the Cuisinart (blender, chopper shredder) of RF.? You always get things you might not want. And often a headache. ;) Allison |
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Hi Jerry,
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The list is having trouble voting? Some of the well equipped techs have given 17 meters a pass. Now you say it is bad. Which is it? 73, Bill KU8H On 08/10/2018 03:59 PM, Jerry Gaffke via Groups.Io wrote:
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