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I just ordered a QDX kit

Pierre FK8IH
 

I just ordered a QDX hi-Bands kit this morning.
After having used several stations in the past (a vacuum tube home made 60 years ago, 40 years ago a Yaesu FT-707 then more recently a FT-897D) now my main station is a Hermes Lite 2 SDR XCVR with an AlexLoop antenna. Wonderful, I enjoy the discovery of SDR radio and the results in QRP with FT8!
Well, after having widely studied the last QRP sets proposals I eventually found the QDX concept awesome.
I plan to use my QDX with my Alexloop, a LiFePo4 battery and a CrowPi-L Elecrow computer (based on a RaspBerry 4B 8Gbit RAM) CrowPi-L - Elecrow
This will make a very portable station, everything holding in the Alexloop backpack. 
The soldering iron is just waiting for the delivery by FedEx.
73 - Pierre - FK8IH
William Smith
 

Not sure about the Alex loop, but magnetic loop antennas tend to have a very narrow notch of low VSWR, so you might want to add an antenna analyzer, as the QDX does not handle poor VSWR at all well.

William Smith
ComputerSmiths Consulting, Inc.
w_smith@...

On Mar 31, 2023, at 12:23 AM, Pierre FK8IH <jb.gallauziaux@...> wrote:

Alexloop
Brad McDowell
 

Agree with the SWR concerns using the QDX with an Alex loop.  A high swr on the loop will blow the finals in a heartbeat.  Ask me how I know.

Brad, AB4BA
Donald S Brant Jr
 

You might consider adding a bridge-type VSWR/power meter to your kit.  The 6dB loss of the bridge will keep the VSWR seen by the radio to under 2:1 with any antenna load, protecting the finals while you are tuning the loop.  I use a QRP-O-Meter, but there are others.  https://www.tindie.com/products/NM0S_qrp/qrpometer/
After tuning, switch out the bridge and transmit at full power.  
73, Don N2VGU
stone_ridge_road
 


Using the QDX with a small loop antenna is a bad idea, as other QDX users can attest.

73,
Dave  AB7E


On 3/30/2023 3:26 PM, Pierre FK8IH wrote:

I plan to use my QDX with my Alexloop, a LiFePo4 battery and a CrowPi-L Elecrow computer (based on a RaspBerry 4B 8Gbit RAM) CrowPi-L - Elecrow

This will make a very portable station, everything holding in the Alexloop backpack. 
The soldering iron is just waiting for the delivery by FedEx.

73 - Pierre - FK8IH
Pierre FK8IH
 

Thanks to all. I already have a QRP Guys Led tuning indicator, which in the Tune position limits the SWR seen by the XCVR to less than 2:1 but divides the power output by 4. In the Operate position there is no loss. Well I can tune my AlexLoop in the Tune position then shift to operate.
LED Tuning Indicator Page - QRPGuys
73 - Pierre - FK8IH
stone_ridge_road
 



Make certain that the proximity of your body doesn't shift the tuning when you switch to your operating position.

73,
Dave   AB7E


On 3/31/2023 3:44 PM, Pierre FK8IH wrote:

Thanks to all. I already have a QRP Guys Led tuning indicator, which in the Tune position limits the SWR seen by the XCVR to less than 2:1 but divides the power output by 4. In the Operate position there is no loss. Well I can tune my AlexLoop in the Tune position then shift to operate.
LED Tuning Indicator Page - QRPGuys
73 - Pierre - FK8IH
_._,_._,_
Pierre FK8IH
 

Thanks Dave, I'm aware of that. The fact to put my hand on the control knob and remove it will alter the tuning. I'm thinking to make a long isolated adaptator. Anyway I love the Alexloop and I got excellent results on FT8 with my Hermes Lite 2 and SparkSDR software. I want to try it with my QDX whan I will get it ready.
73 - Pierre - FK8IH
stone_ridge_road
 

Sounds like a good plan!  Hope it all works out well for you.

73,
Dave   AB7E

On 3/31/2023 9:10 PM, Pierre FK8IH wrote:
Thanks Dave, I'm aware of that. The fact to put my hand on the control knob and remove it will alter the tuning. I'm thinking to make a long isolated adaptator. Anyway I love the Alexloop and I got excellent results on FT8 with my Hermes Lite 2 and SparkSDR software. I want to try it with my QDX whan I will get it ready.
73 - Pierre - FK8IH
Pierre FK8IH
 

Dave, I use also a UnUnantenna of QRP Guys with a Phoenix MTM transmatch of Kanga products.
QRPGuys 40m-10m UnUnTenna - QRPGuys and MTM-ATU (KIT or Fully built) The QRP Transmatch ATU (kanga-products.co.uk)
The transmatch shows also a SWR <= 2.0 in Tune and can be bypassed when the Un antenna is tuned. Well, but the AlexLoop is still my prefered one and since QDX works on only in a very narrow band with FT8 or JS8 it should be nicely fit,... but I shall watch the SWR!!!
73 - Pierre - FK8IH
Pierre FK8IH
 

Thanks to all. Well I'm very much aware now of the SWR issue with the QDX. I did not think so much to SWR with the Hermes Lite 2 as its Power Amplifier uses AFT05MS003N LDMOS and they accept a SWR<=65:1 and I actually faced such high SWR without damage when tuning my AlexLoop!
73 - Pierre - FK8IH
Pierre FK8IH
 

I'm ordering a NanoVNA in order to always thune my antenna precisely on the frequency I will use before plugging the QDX in it and transmitting. By the way my QDX- HB has arrived in the island and should be delivered by Fedex next week. I am in a hurry to get my soldering iron out of the toolbox.
73 - Pierre - FK8IH
pgramsey@...
 

Be sure you have a good magnifier. I don't think it's possible to build one of these without one. You'll need it to identify those tiny parts and to check the solder joints, especially to verify that there are no solder bridges.
Pierre FK8IH
 

Thanks to all for your comments. My kit arrived yesterday and I have everything now to start building following your comments : tiny tip soldering iron, tiny solder, magnifier. I'm still waiting for the delivery of a NanoVNA-F I ordered a few days ago.
When the QDX is ready I'll use it with my UnUn antenna (QRPGuys) and Phoenix transmatch after testing the SWR with the NanoVNA. I plan also to use my AlexLoop, which is very efficient, but only after setting it perfectly with the NanoVNA (I have seen with my Hermes Lite 2 SWR reaching more than 50:1 when setting the Alexloop but the HL2 power amplifier accepts up to 65:1, yes I saw it without damage!).

73 - Pierre - FK8IH

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