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Swap my 17m QCX Mini for a 20m or 40m one?
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Martin Peters
Has anyone got a 20 of 40m QCX Mini they'd like to swap for my 17m metre version?
I built mine a few months ago but the drift on WSPR was too high. So I ordered the TCXO, which I fitted today. Zero drift! However, on 18MHz I'm limited to the end fed wire and the RF in the shack blows my speaker off the shelf and locks up the PC. So I think I'll have to use the full-size 40m loop and let the feeder carry the RF outside! Hence the 40 or 20m request. Mine is as-new, measured 3watts out on a 13.8v supply. UK-only, please. Thanks - Martin, G4EFE |
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Martin DK3UW
There should be ways of getting the RF out of the shack. What kind of transformer do you use at the end of the wire ? Is there a choke on the Coax ?
If your end fed wire is a half wave long with a 49:1 transformer and a choke at 0,05 wavelength from there on the coax, you should not have any HF in the shack. I have no QCX to offer but why give up on a rig, when the antenna is the problem ? 73's Martin DK3UW |
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Bryan Curl
On Tue, Nov 22, 2022 at 09:19 AM, Martin DK3UW wrote:
There should be ways of getting the RF out of the shack. What kind of transformer do you use at the end of the wire ? Is there a choke on the Coax ?Martin is correct. I have a par endfedz for 20. I had rf fritzing out and locking up the display on my qcx+ . I made a 1/2 wave feedline and put a 1:1 unun choke there. Then another length to the rig. No more rf. I also broke into the box at the antenna and found a tuned circuit, not a 49:1 balun. This was tuned to 14350 so i added a small chunk of rg316 across the cap and trimmed it using my nanovna until the circuit was resonant at 14050. Final length if the stub was about 1". This greatly improved swr after adjusting the wire element length for 14050. -- regards, Bryan, N0LUF |
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John Kirby
Martin
I agree 1st) the antenna **length** 2nd) the feed line **length** can push rf back into shack May I suggest a solution for end fed wire that can and will solve either and/or both reguardless of length of either verses operating freq "THE >L< NETWORK REVISITED" drop down on this page to my call >>>https://www.qsl.net/ve3mcf/elecraft_reflect/Antenna_Random_Wire.txt<<< If coax fed then a transformer is required I use a 1:4 between coax and 132ft long wire More on The L Network with respect to my configuration Figure 6.4.1 only ..a.. and ..b.. >>>https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Microwave_and_RF_Design_III_-_Networks_(Steer)/06%3A_Chapter_6/6.4%3A_The_L_Matching_Network<<< Ports on the MFJ 16010 can be swapped (input/output) for both examples in Figure 6.4.1 ..a.. and ..b.. I have a couple QCX willing to swap de other side of the 'pond' Both modified for several bands You can do same by swapping out the LP-Filter >>> https://www.qrp-labs.com/lpfkit.html<<< 72 73 John N3AAZ |
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On Tue, Nov 22, 2022 at 04:19 AM, Martin DK3UW wrote:
There should be ways of getting the RF out of the shack.A quarter-wave counterpoise comes to mind. 73, Don N2VGU |
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alvey street
take about 14 feet of wire. spread it around or run it straight out of the shack. Connect one end tothe gropund point / chassis/ co-ax outer near the rig. That should choke off any RF in the shack.
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Martin Peters
Thanks, everybody, for your input, and advice re reducing the RF in the shack. This is something I'll need to address in the near future (good job I'm exclusively QRP or things could get hairy!).
In the meantime, someone off-list suggested I should re-work the QCX for another band, which is exactly what I'll be doing (for 20m). Thanks again and 73 - Martin, G4EFE |
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Martin, As an old timer in these issues I would recommend getting the RFI out of the shack first as it will cause problems no matter what rig or band you use. I still have an old Heathkit RF indicator and just move it around the shack and adjacent rooms in my house to detect stray RF. All or 99% of your RV should be going out your coax to the antenna. The QRP Guys have (had) a digital RF detector that works also. Some of the older SWR bridges have a short antenna wire sticking out of the box for that purpose too. Clean up the shack floating RF first and then there will be fewer problems in the future. Dave K8WPE David J. Wilcox’s iPad On Nov 22, 2022, at 2:55 PM, Martin Peters via groups.io <martin.peters@...> wrote:
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