Have a look at?
I¡¯ve built 7 and they work very well. Coax input and outputs are grounded through the coil. I¡¯ve printed 45-60mm diam toroids and also have used a T130-0 you can get quite a good L value.?
I¡¯ve converted a few people to them. I only use Airwound toroids so no losses in iron powder.?
?I¡¯ve used in my travels quite a bit and all but one use polyvaricons as caps.?
73
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On 29 Apr 2023, at 13:11, mux_folder2001 <canthony15@...> wrote:
?
I have only had my HB for about a month and I have blown a couple of PAs due to matching issues. That aside, this QDX is FANTASTIC! The design is remarkable and well executed. I love the electronic aspects of the hobby so I always end up fiddling with things
but I would be proud of this design if it were mine. Just amazing what was done for the price. This thing makes me happy! I have ordered another for the low bands.
Tony
AD0VC
Dave et Al,
I have used the first prototype High Band since I designed the filters last year. I used at the home QTH and then took it to QRP Labs HQ for assessment and ultimate implementation. I have used that and another HB almost continuously. I¡¯ve operated with
it portable in Prague, Rome and Istanbul with various wire antennas out hotel windows on fishing rods and wires on lead sinkers slingshotted into local trees. I used to use a small 12V PS with a variable buck down and meters but now, due to noise reduction
measures, I run all my QDXes and RaspberryPIs on Lithiums, 2 in series that start at 8.4V and I usually change them and recharge when somewhere at 7.3V. RasPis I use a 30,000mAH power bank.?
The one thing I am very careful about is antenna matching. I used to use LC matches with plastic printed spherical variometers as the variable L. I now use FRI-matches with 3D printed large toroids. I also have a switch that puts a LED swr bridge in line
and a switched LED current monitor antenna wire.?
The first and original HB QDX is still going strong! It was built for 9V but usually operates at an average of 7.8V.?
Careful management of the antenna match is the most critical to long QDX life!
73
Ross
6
On 29 Apr 2023, at 07:25, Hans Summers <hans.summers@...> wrote:
?
Hi Dave, all
The washer isn't the heatsink. The heatsink is the PCB. The washer and bolt are just the mechanical means of bolting the flat side of the transistors to the PCB.
As others have said... Thermal paste doesn't harm but doesn't make a lot of difference, either. Be careful too because some pastes are electrically conductive and that won't go well. Make sure you don't use that.
Personally I have found the QDX PA reliable and durable as have many others. A lot of failures have posthumously been attributed to sustained chronic SWR mismatch or acute mismatch during auto tuner use, supply spikes etc., over-voltage, including
from fully charged 12V-nominal batteries.
Remember also that on any forum such as this one, you will tend to hear far more frequently from people with a problem, than those without. You tend to get the mis-impression consisting of the proportion of people with problems, out of the collection
of people with problems. The actual proportion of people with problems, out of the total of all users, is a lot lot lower (and difficult to quantify).
73 Hans G0UPL
On Apr 29, 2023, at 8:45 AM, Dave Sergeant G3YMC <
dave@...> wrote:
Humour aside Razvan does have some valid points. I have not yet put my
QDX into transmit mode but already have concerns about the design of
its PA stage. The requirements for not exceeding 12V (in a 12V HB
version) or daring to transmit into anything other than the religious
50 ohm load is an indication that the design is maybe just a tad close
to the limits for comfort. It almost made me laugh when I attached the
little washer to the rounded side of the BF170s asking myself if I had
mounted them upside down. Surely you should put the heatsink on their
flat side I asked.
In the desire to make the thing as small and cheap as possible it seems
common sense has been overlooked. A couple of TO220 case devices on a
slighly bigger board and a bit more metal to heatsink them would have
made a far more robust PA and removed the need for all these
discussions on this reflector.
No criticism of Hans of course, the QDX is an incredible little rig,
but as an engineer in my professional life I would have not done it
that way.
73 Dave G3YMC
On 28 Apr 2023 at 15:15, DL2ARL wrote:
you could also sprinkle over the BS170s some Water out of the Holy
Fountain of Lourdes from
southwestern France. It would help as much as thermal paste, but it
will have the big advantage of
not doing no harm and cost less.
