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Re: PA transistor Heatsinking of a uBITX
#ubitx
I switched to the RF16HHF1 output transistors and this allowed me to directly bolt them to the heat sink.? I used one large heat sink for the two of them. This heat sink is bolted to the box I put it in.? I was lucky in one sense in that the box was just the right size to have the display out the front and the board just fit to the back of the box.
While not as nice looking as many of the others, you can see what I did here:? One pix is with the original transistors and one is with the larger heat sink.
Mine is near the end under my call of KU4PT
On Sat, Jun 9, 2018 at 8:06 AM, Peter LB0K <lb0k@...> wrote: I can see the insulation argument to why these are installed hanging on to the IRF510s but this puts a large mechanical load on the transistor legs and increases the risks of damage, especially if one tried to use the uBITX as a portable, even as a SOTA rig.
?
One could fit a larger common heatsink that was fixed to the chassis/casing or PCB and one would then have to include rectangular insulating washers between the transistors and the heatsink.
These changes would increase the parallel drain(s) capacitance to ground, etc. etc.
?
I envisage these positive results:-
-?????? better mechanical strength
-?????? a more robust construction
-?????? easier to provide controlled cooling of the heatsink.
?
?
What sort of negative results should/could one expect from these measures?
?And how to fix'em?
?I envisage these negative results:-
-?????? a slight increase of weight
?
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Re: PA transistor Heatsinking of a uBITX
#ubitx
Peter,
Aside from logistics (a plastic case, rear of cabinet too far from board, etc.) there is no downside. I do this on most of my BITX's, whenever possible, and it is the superior choice. No need for a heat-sink other than the metal case itself. It hardly gets warm at all at maximum power. Much more robust mounting. Lighter weight. Just use standard TO-220 mounting hardware including the insulators, a little heat-sink compound if you use a mica insulator. Cooler than the supplied heat-sinks by far.
73, Don
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Re: The new uBITX boards are here
My Yaesu HF rig is jealous.? Since I received my uBITX v3, I have been spending all of my ham radio time with it instead of my main rig - it's so much fun.? Thank you Ashhar for such a great product at an affordable price!
So much fun that I have ordered the v4 board.? I tried to make some of the mods to my v3 but I don't have the tools to work with surface mount devices (and I damaged my board trying to remove a capacitor - some creative soldering got it back working again).
Questions:
1) Is the mounting hole pattern for the v4 board the same as the v3?
2) Were the Raduino and analog connectors moved?
I ask about the board hole pattern and the connectors because I bought one of the 'amateurradiokits.in' enclosures to house my uBITX.
3) Is there a test point where an S-meter signal could be obtained?? So I can use this feature in KD8CEC's firmware.
Thanks,
John
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Re: Another uBITX in a wooden box
On Saturday, June 9, 2018, 9:21:57 AM EDT, Lee <mr.olson@...> wrote:
Very nice.? I wood use a radio like that. -- Lee - N9LO? "I Void Warranties"
?
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Re: Another uBITX in a wooden box
Very nice.? I wood use a radio like that. -- Lee - N9LO? "I Void Warranties"
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Another uBITX in a wooden box
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Perhaps these practical BPF hints could be of value
Ulf SM0CGL
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Re: RF power chain mods and improvements..
Attached is my driver it goes between
VR1 and the outputs of T10 you need to remove C84 and T10 and
insert this circuit. I am using the AMP signal to reduce the
overall power output when driving a linear amp which needs 5W not
10W. U7 is a current driver, I chose it because I have a number of
them, I probably could select something better, or use an emitter
follower but it should do the job at 0 cost for me. The same with
the T13-1 transformer, I have them. The opamp was selected for its
speed slew rate voltage and current drive capability. C45 is there
because U7 needs a minimum load capacitance for stability. I will
see if I need to add something there later. TX is the switched 12
volts that is there in transmit only.
I am working on a PCB with this being one part of a daughter board
for the uBitx. I would be interested in any feedback. I am not
suggesting that this is a cost effective way of improving the
uBitx for production. I will post the entire schematic in a few
days.
Howard
On 6/8/2018 11:50 PM, Jerry Gaffke via Groups.Io wrote:
toggle quoted message
Show quoted text
And if you really
wanted an MMIC for the pre-driver,
here's a cheap one capable of 18dBm.? $0.55 each if you get a
reel.
? ??
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Re: RF power chain mods and improvements..
The MMIC has a absolute maximum voltage
of 4.5 VDC. Assuming you use a transformer (actually you must to
get the drive level you need for the output stage) you an only use
a +2 volt supply for the device for a 4 v p-p swing. So you need
at least? 1:2 step up transformer so the driver needs to source
more current to drive it. I am completing the design of a driver
that is flat to 30 MHz and will post it soon. It uses a current
driver and a dual opamp replacing everything from VR1 to T10.
Howard
On 6/8/2018 11:50 PM, Jerry Gaffke via Groups.Io wrote:
toggle quoted message
Show quoted text
And if you really
wanted an MMIC for the pre-driver,
here's a cheap one capable of 18dBm.? $0.55 each if you get a
reel.
? ??
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PA transistor Heatsinking of a uBITX
#ubitx
I can see the insulation argument to why these are installed hanging on to the IRF510s but this puts a large mechanical load on the transistor legs and increases the risks of damage, especially if one tried to use the uBITX as a portable, even as a SOTA rig.
?
One could fit a larger common heatsink that was fixed to the chassis/casing or PCB and one would then have to include rectangular insulating washers between the transistors and the heatsink.
These changes would increase the parallel drain(s) capacitance to ground, etc. etc.
?
I envisage these positive results:-
-?????? better mechanical strength
-?????? a more robust construction
-?????? easier to provide controlled cooling of the heatsink.
?
?
What sort of negative results should/could one expect from these measures?
?And how to fix'em?
?I envisage these negative results:-
-?????? a slight increase of weight
?
?
?
?Peter
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I would like to add my kudos to Kees for the neat board and micro smd parts. ?Glad I have magnified loupes and can still see them yet. ?Well done my friend. ?A sneeze and they will be history. ?Use a raised edge cookie sheet. ?Also, no cats allowed. ?They stick to paws........?
Also, if you ordered two of each they will come in separate envelopes on different days. ?Two kits to an envelope.
Dave K8WPE
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On Jun 8, 2018, at 4:17 PM, Mark M < junquemaile@...> wrote: Let me add my thanks as well. I received the kits yesterday and am quite impressed. I was expecting only a set of parts so was pleased to also get the schematic, etc...even a little piece of double-sticky foam tape. Now to see if I can assemble them...those surface mount parts are really tiny.
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Here is a filter designed with SVCFilt (at least a 20 years old ARRL programme) under Windows95 (hihi). Capacitors can be any ceramic (usually are rated at 50v) and inductors may be built with or without a toroid.
Il 09/giu/2018 08:31, "iz oos" < and2oosiz2@...> ha scritto: Many tuners are rudimentary highpass filters, especially at 28mhz, the spur may be far away to be attenuated somehow. Also a monoband may further attenuate that spur. To keep it as simple as possible I would use an external high pass filter. Just plug and play.
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Many tuners are rudimentary highpass filters, especially at 28mhz, the spur may be far away to be attenuated somehow. Also a monoband may further attenuate that spur. To keep it as simple as possible I would use an external high pass filter. Just plug and play.
Il 09/giu/2018 01:06, "Arv Evans" < arvid.evans@...> ha scritto: Once you now what the probable frequency of spurs it is relatively easy to monitor
them with another receiver.? Even something as simple as the Pixie circuit will work
if you provide stability and accuracy with a DDS or Si5351 as its local oscillator.?
Well shielded auxiliary receiving devices can be calibrated by inserting a step
attenuator in the antenna input and measuring audio beat note level of the output.?
This could be the basis of a poor-man's spectrum analyzer.?
Arv
_._
Wow!...All the feedback here has exceeded my expectations.
Alyson,? I'm truly impressed that you were able to "Dumb" this down to an understandable level.? I've learned quite a few things in this thread that have been pestering me for a long time.
I'll consider trying a filter,? but not until I figure out how to monitor for the spurs. What's the point unless I can confirm that it's working, right?!? But I won't pester you all with that right now.? I'm sure the answer to that is somewhere on the board.
I'll keep watching for a consensus on the issue.
Thanks to everyone!
Maybe some other noobs will benefit? from this as well.
David
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Re: pcb for modifications ver3 to ver4
Sprint layout file uploaded to file folder GL
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Re: RF power chain mods and improvements..
Allison, thanks for the heads up on EB63 design. I will avoid it and think about something similar to the Hardrock-50. It is a modern design and the parts are inexpensive. I will probably build the amp just to cover 40 and 20. Low pass filters at the input to the amp and 3 section LPFs on the output should be sufficient. An attenuator for each band on the input would take care of the difference in output levels of the uBitx.
Out of curiosity I will look at the uBitx output with the DSA-815 sometime this weekend.
Ray
AB7HE
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These are inverse exponential responses, it won't be symmetrical.
But the pot should help move it toward vaguely similar rise and fall rates.
The integrator mentioned in post 50445 is capable of creating a very nice trapezoid.
We had a discussion on this going in the AT-Sprint group over a decade ago:
? ??
where we found a way to make the rise and fall slopes of the trapezoid equal,
and also how to make the slopes constant when the power supply voltage varied.
Way overkill, most of us should just stick with the cap and resistor.
?
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Show quoted text
On Fri, Jun 8, 2018 at 09:17 pm, Jerry Gaffke wrote:
If you want the rising and falling edges to be symetrical,
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Cool that all it took was a larger C1, that's a good result. From the scope traces, the rising edge is much faster than the falling edge. This is because the CW-KEY line from the nano is rising exponentially from 0v to a 5v asymptote it is travelling very quickly through that first fraction of a volt where the mixer becomes unbalanced. On the trailing edge, CW-KEY is starts travelling quickly as it makes its way exponentially down from 5v, slowing as it asymptotically approaches 0v. If you want the rising and falling edges to be symetrical, try adding a 1k pot across C1, this forms a voltage divider with R104 so you can adjust the maximum CW-KEY voltage that gets presented to C1. Adjust the pot for symmetry in your scope display, then measure the pot and replace it with a fixed resistor. resistor across C1.? ?First suggested in post?? /g/BITX20/message/50445?
On Fri, Jun 8, 2018 at 08:48 pm, Allan Mason wrote:
All that was required was to increase the value of C1 from 0.1uf to 1uf.
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Re: RF power chain mods and improvements..
And if you really wanted an MMIC for the pre-driver,
here's a cheap one capable of 18dBm.? $0.55 each if you get a reel.
? ??
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This email is for?those interested in using the transceiver for CW.?
Being mainly a CW operator, I was concerned about?the?V3 board uBitx transmit CW wave shape?being very hard with an almost square waveshape?and as expected, key clicks could be heard on?either side of the signal. A look at the circuit diagram and a little tinkering today vastly improved the situation.
All that was required was to increase the value of C1 from 0.1uf to 1uf. Attached are some CRO photos of the end result showing the leading edge and trailing edge of the transmitter output with a 1uf connected across C1. The other photo?shows where a short wire was soldered to the hot side of C1 for the tests.? In reality?the wave shape?is now a little soft on the trailing edge, so 0.047 or 0.68uf may be sufficient for some people.?? More work could possibly be done with the CW keying RC network to the?1st balanced mixer, however?this one component?simple fix will suit my needs.
The tests were contucted using the internal keyer set to 25wpm. The CRO connection point was at the antenna BNC connector with a 50ohm dummy load.
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Don, ND6T
Lee
David Wilcox K8WPE
Allan Mason
