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Multiband QCX
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Hi Folks,
we want to experiment creating a multiband QCX. Which would be the best version to start from? I have seen that now you can change the QRG in 1 Mhz steps. Would that mean you can just move to another band and it would work more or less. What would need to be adjusted I found some hints on the forum but its so split up into different topics, that I got lost. Mabe it would be worthwile to get all that informtionin one topic. QSX would be nice but a multiband QCX would do for me. 73s Martin DK3UW |
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Likely the 80 or 40M version, however they are all the same save for the tuned circuits.
Starting point? would be T1 made untuned then the RX wors on many band limited by the LPF filter.? If broad cast breakthough is an issue then a highpass filter with a low frequency cutoff of 1.7mhz is needed.? Also 160M can be done but due to the handling of the Si5351 opposing sideband rejection is not very good. I'd limit RX to 80 through 10m? The TX is far harder, because to get efficiency out of the class E the fets it have to be? feeding into a tuned matching system?so really a LPF for each band d esired and also L4/C30 as a pair for each band. TX on 160 is doable, 10M may be very poor on power out.? ?To do all this a band switched output filter is a must (Its also used by the RX). Building several would likely be easier as 80M and 40 is rather poor during the day, 30M holds up ok at night, and 20M fades at night. 60M is also possible but CW only (USA). Allison -- Please reply on list so we can share. Off list email goes to trash, I had to due to scrapers. |
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Hi Martin,
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Now QCX have CAT control :) and you can use some external Arduino to change band(freq) and LPF (BPF) filters. Or you can use some manually tuned BPF similar to: T1 eliminated as in previous link (tnx Guido!). 73 es GL with your modifications, Andy ua9/9a3jh On 11/29/19 7:00 AM, John Kirby wrote:
Martain, |
¿ªÔÆÌåÓýHi,I build a 30m QCX. For multiband i use the TRX as IF stage. Adding one oscillator and mixer, pa and some filterung of course and the multiband is done. I know that this solution is not a ?change four parts¡° solution, but in my case with the 30m QCX version (10MHz) it seems to be a good idea. Best 73 Denis DL5SFC Von meinem iPhone gesendet Am 28.11.2019 um 22:45 schrieb Martin <m.sellschopp@...>:
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On Fri, Nov 29, 2019 at 01:00 PM, John Kirby wrote:
Martain, This post by VK3IL has some interesting insights into the challenge of multibanding the sodapop, a rig by KD1JV that has a similar PA architecture to the QCX. On the receive side this article has some interesting things to say about the tracking bandpass filter nature of a QSD front end. Ie equivalent to single pole filter with Q of 3500. And goes on to suggest that only low pass filtering may be required as the QSD IS sensitive to aliasing of the harmonics. https://www.google.com.au/url?sa=t&source=web&rct=j&url=https://wparc.us/presentations/SDR-2-19-2013/Tayloe_mixer_x3a.pdf&ved=2ahUKEwi33-fLvY7mAhVHAXIKHZQFBGwQFjABegQIBhAB&usg=AOvVaw1ku_aXA5nNAaGQQ_JfPOwn It does seem that multibanding with neighboring bands that are within the cutoff frequency of the low pass filter of the lowest band of operation eg 30m and 40m could be built without the bpf and using only the lpf for the lowest band could work with reasable PA efficiency and little impact on receive. Alternatively, if you wanted some filtering of the low end the bpf could be reconfigured as a hpf. 73? Simon VK3ELH |
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There are a few people who've tried to multband the QCX before, and it seems to be pretty easy.? In regards to the receive chain, T1 and the bandpass filter are the crux.? Some people have gotten around it by switching in more capacitance as needed to change the BPF peak (my favorite example of this is a varactor diode with a trimpot to really dial it in.)? Others have replaced the iron powder core with ferrite and a simple trifilar winding to maintain the balanced input but eliminate the BPF.? Still others have unbalanced the input entirely (like Guido PE1NNZ did: /g/QRPLabs/message/38064).? I seem to recall somebody else adding a socket to T1 so they could plug in different modules, but I'm afraid I can't find a reference.? Most approaches seem to work reasonably well and nobody has reported a significant degradation of performance so far.
Good luck! John VA7JBE |
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Hi,
the "Lima-SDR" of German OV Duisburg, L02, probably has a suitable multiband preselector (and optional preamp) for the RX. The Lima-SDR works quite similar to the QCX. Many documents of this RX are no longer available on the web, I'll post the schematic below. You can see the preselector here: https://www.dl1smf.de/de/node/2, first image, the lower section. OV U02 and DJ0ABR have improved the preselector and made a very good one, but 1.) the original preselector is probably good enough and 2.) the description seems no longer available on the web. There was also a TX, including a low pass filter, for Lima-SDR, but couldn't find the docs online anymore. (I have the complete RX-docs for I've built it, in German, but no TX-docs.) U02/DJOABR have an improved Low-Pass for Lima-SDR-TX, doc is here: https://www.helitron.de/dj0abr/ > "Lima SDR und FA SDR ausgebaut" > "TX-Tiefpass" Maybe, it is worth to take a look at the lowpass of KX2, saw it on the web recently. Maybe, you could even get PCBs for preselector and TX-Lowpass from DJ0ABR. As on how to handle the inductance at drain of the BSS170-Final stage, I don't know, could be difficult. I'm quite interested in your work of building a multiband QCX, so would be glad to hear about your ongoing work. Kind Regards, Axel, DF1ET |
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Hi Folks,
thanks for the many good hints. So the final concept is not yet clear and I am not the technical brain behind it. As a start I ordered a QCX 40 and BPFand LPF for 5 bands. As a first step I then will be busy competing the QCX without the obligation to wind toroids but there will be some waiting for the filters. Change band via CAT ? I have a laptop but now idea on what has to happen between the QCX and the laptop. I use Swisslog and N1MM as softwares. I thing easyest will be to use the 1 Mhz steps. Axel, any doc in German would be fine 73s Martin DK3UW |
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Two things easily broken on QCX:
TR switching so that QSK is not as good. RX overload capability.? Too much preselector gain below 20m is a problem, for 17/15/12/10M it may be desirable but with care.? I'd suggest maybe 10db or less below 20M. For most I've modified mine to have an untuned trifilar transformer at T1 and the performance is good this way.? Prefixed by a bandpass network would help?for difficult situations but I've not experienced that. The reason for not using a tuned circtui there is changing the tuning can markedly change the opposite sideband response. One item missed is sideband switching for over 10mhz.? As wired its LSB only.? ?One way is flip the LO phase (in menu). Allison -- Please reply on list so we can share. Off list email goes to trash, I had to due to scrapers. |
"untuned trifilar transformer at T1 Robin HB9DEF did this about a year ago, it's basically the same winding you'd find on a normal T1 without the 3rd secondary (the one with lots of turns), and using a ferrite toroid instead of a T50-2 (Robin uses an FT37-43).? Here's the post: /g/QRPLabs/message/27786 Cheers, John VA7JBE |
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Hi Martin,
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I am not familial with Swisslog but with N1mm+ should be easy. Connect QCX to serial port, open n1mm+, go to config/config ports,.../hardware, choose your serial port, choose radio ts480, click set and set speed 9600, ok. If you don¡¯t see QCX freq in N1mm+ maybe have to restart n1mm+. In N1MM main window on left side click band and your rig have to change freq/band, or connect to dx cluster(telnet) and click on spot and rig will change freq, or click on bandmap and change freq,etc 73 GL, Andy ua9/9a3jh On 12/1/19 12:45 AM, Martin wrote:
Hi Folks, |
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