You simply did not scroll down on the join/renew page to find the member lookup which is there¡ªI checked. And why post your problem on the tech list¡ªwith the caps button on?
Preston Douglas WJ2V
President QRPARCI
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dID WE NOT HAVE A MEMBER LOOKUP ON THE HOME PAGE?
yES, i FORGOT MY NUMBER. Did we take that function off the web?
Mike Baker K7DD
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Re: QRPGuys DSB Digital Transceiver
Then the approach I'd take is try it... IT might succeed far more than
expected.
Allison
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Re: QRPGuys DSB Digital Transceiver
Looking for something more durable and easier to heatsink. I never cared
for heatsinking TO-92 devices (not effective in cooling the die) and three
in parallel was never a favorite technique for me. This smells of value
engineering. I'd rather pay another couple of $$ on the kit and do it more
robust fashion than it is now.
Randy.ab9go@...
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Re: QRPGuys DSB Digital Transceiver
Why?
Unlikely to give more power as its gain is lower than BS170s,
If anything less power as you only can get so much from the
2n3904. It would be easier to heatsink and likely more durable.
The layout and mechanics of that mod might be a pain as well.
Allison
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Re: QRPGuys DSB Digital Transceiver
I was wondering about the use of an IRF-510 to replace the three BS170's.
Other rigs use this device successfully. What do you think?
I ordered the kit today.
Randy.ab9go@...
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On Fri, Oct 4, 2019, 12:23 PM Randy AB9GO <randy.ab9go@...> wrote: Good morning all,
I was thinking of buying one of these little devices and I had the same
questions in my mind about the DSB mode of operation.
The other thing I was questioning is the design of the final output stage.
I know it's been a tradition in ham radio to either parallel tubes or
transistors to get the wattage rating that you need, but in this case there
should be a single mosfet that can do the job is economically as three? In
addition I like to heatsink the output devices and this really doesn't lend
itself to effective heat sinking. Other than some gimmick add-ons for
TO-92's, were never really designed to be heat sinked. (I know that some
TO-92 devices produced with a small heatsink tab, but that's not what we
have here from the kit pictures.)
Does anyone out there have a suggestion for a sutible single output device
in a TO-220 form factor or similar?
Thank you,
Randy ab9go
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Thanks for that explanation Allison.
I'm not trying to fix a problem, I was just curious about the discrepancy in the resistor value, but it seems it's not critical and could just as well be a short circuit to ground.
Likewise it is now apparent that I can do away with the series capacitor!
73,
G3KSU
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The 80185 board I have has 10 ohms but since its at the center of the
balancing transformer it seems that its more or less odd to be a resistor
at all and direct to ground.
My Argonaut 505 uses a very similar circuit but that resistor is 3.3 ohms.
I don't understand your comment on DC short circuit. The caps C4 and C5
break the DC path for the finals. A tuned loop (TX) does not have any need
for DC break.
What problem are you trying to fix?
Allison
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Could some kind fellow-owner please check the value of R5 on the RF Power Amp Board (80185) in a TenTec 509?
The CIRCUIT indicates TEN Ohms but mine is color-coded & measures ONE Ohm.
No need to dismantle anything: It can be measured (near enough) across the ANT SKT & via the Low Pass Filter/SWR Bridge Board (80260), unless you have fitted a series capacitor to isolate the DC path presented by a Mag Loop Ant.
BTW, having said that, I ran the rig into a Mag Loop for about twenty years before I discovered it was looking into a DC near short-circuit!
And while I'm here, does your 'S' meter bang hard over when the key is pressed?
73,
Alan Williams
G3KSU
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Re: Idle current, QRPGuys DSB Digital Transceiver
Gang,
Looking at the figures I posted earlier for the 40m output, they looked high compared to some earlier figures, and I have been unable to match that output or to account for the discrepancy. A more recent measurement matches the 20m and 30m values but the revised 40m output to a 50 ohm load is 2.56W, using Steve's recommended setup procedure, with a 12.0v supply and transmit current of 590mA.
ken - wa4mnt
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--
William, K6WHP
"Cheer up, things could get worse..so I cheered up and, sure enough, things got worse!"
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Re: DSB transceiver heat sink
Not a thermal designer, but have considered best way to heatsink epoxy-molded parts
like TO-92 BS170...
On the one hand, the chip is bonded to the DRAIN pin, so some heat is efficiently
conducted out the drain leg...much less heat to GATE or SOURCE pins. It might
be helpful to solder a copper "flag" to each drain leg.
On the other hand, these chips have significant area. Couldn't find BS170 die area,
but the IRF510 chip area is 2.5x2.21mm. If anything, BS170 is smaller. A large-area
chip transfers significant heat to epoxy. So Chuck's heat-transfer via the flat side of
the TO-92 is a good plan.
Where 3 BS170's have their gates biased near threshold voltage, red flags start
waving in my mind. Some BS170 data sheets show threshold voltage range
from 0.8V to 3V while others show a smaller range (0.8V - 2V). If you blow one,
consider replacing all three, and hope they're all from the same batch so that
their gate threshold voltages are similar.
Another concern is that gate threshold V is temperature-dependent. Should one
of three be poorly heat-sink'd, does it not tend to hog when biased near threshold?
Using one IRF510 seems safer.
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Re: DSB transceiver heat sink
Its adequate until the battery drops to or below 11V and then the 7809 stops
regulating. The 7809 needs more than 2V across it or 11V input to regulate
acceptably. Of course then the only risk is a dirty signal as the PA goes
class C.
Allison
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Re: DSB transceiver heat sink
"...Setting the bias correctly is critical and using a stable bias
source (its unregulated) will have the device bias vary with battery/power supply
voltage.? A 5.1V zener across V1 variable resistor is not an unwise idea."
The bias source is provided by regulator U3 through L4. Is that not adequate?
73.......Steve Smith WB6TNL
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Re: DSB transceiver heat sink
If one is running the BS170 as something close to linear the power out will be
limited and heating is problematic. Since the to92 case and variants used have
poor heat transfer ability adding heatsinks tends to be less effective in increasing
power dissipation. Setting the bias correctly is critical and using a stable bias
source (its unregulated) will have the device bias vary with battery/power supply
voltage. A 5.1V zener across V1 variable resistor is not an unwise idea.
QCX has the advantage of class E finals so the power dissipated is low as they
are run as switches.
As to driving the IRF510 is one pays attention its fairly painless and a single
BS170 or 2N2222A would easily supply enough drive to get several watts.
The input capacitance of MOSFETS is mostly a red herring, it exists but
is only a factor for switch mode drives. That and I find they do well even
at low VHF.
Allison
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Re: DSB transceiver heat sink
Hi Chuck, all
In my opinion the BS170 is a great part. It is perfect for the QRP PA
stage. They are very low cost and just perfectly placed to make an optimal
QRP transmitter. By which I mean - if you go to higher power capability
then the gate capacitance goes up and it gets harder to drive. Parallel
three for the easiest no-fuss 5W you've ever made.
I use three BS170 in parallel on my 5W CW transceiver QCX kit
. No heatsinks are needed for ordinary CW
operation. In almost 3 years designing/using the QCX (since Feb 2017) I
haven't ever managed to blow a BS170. I've had various mismatches, shorts,
open, and of course good match or dummy loads normally. I don't know why
but these BS170s just keep going and going.
The IRF510 is another great part, for higher power. Again low cost and
easily available. I'm using a pair in my 10W Linear kit and in that
application they've shown themselves immune to any possible abuse,
continuous key-down indefinitely, 20W output, mismatches you name it. All
for under a $ for the pair, and with plenty of change.
Off topic here... but I've been running a pair of IRF510s push-pull
delivering well over 50W RF output all summer here on 40m CW; nearly 500
QSOs and again perfectly reliable.
Bear in mind too that there is a big difference between doing a one-off
homebrew project where cost is of no consequence; and a kit where cost is
absolutely critical.
73 Hans G0UPL,
BS170 and IRF510 lover!
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Re: DSB transceiver heat sink
On Sat, Oct 5, 2019 at 11:36 AM, JT Croteau wrote: From the 100219.pdf manual, the pictorial shows them vertical but the
instructions still say to mount them against the board Thanks, JT. Guess it's time to polish-up my ol' 'cheaters' :-P . Then Chuck's thermal tape might be the simplest solution. 73.......Steve Smith WB6TNL
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Re: DSB transceiver heat sink
Steve,
From the 100219.pdf manual, the pictorial shows them vertical but the
instructions still say to mount them against the board:
"Q3, Q4, Q6 ¨C These parts require some heat sinking. Therefore, these
parts get mounted with the flat side of the package pressed against
the large, tinned pad to the left of the board. A stiff piece of wire
can be used to hold the parts down against the pad by using the two
mounting holes on either side. A better method would be to use a piece
of aluminum, secured with 4-40 screws, using the mounting holes on
either side."
N1ESE
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On Sat, Oct 5, 2019 at 1:27 PM sigcom1 <sigcom@...> wrote:
chuck adams via groups.io
"The QRPGuys new DSB transceiver requires the 3xBS170 FETs
to have some heat sinking. Attached is photo of my solution."
Good idea. Does the production board still have the copper fill area next to the FETs
as in the photograph? The reason I ask is that the pictorial layout and the instructions
(man. 100219.pdf, pgs. 3, 4 & 5) has the FETs mounted vertical .
"So I'd recommend a 22V zener or higher at 1W rating across the PAs."
I too noticed the lack of a protection Zener. This bears some experimentation, IMO. I'm wondering how
the added capacitance from the Zener might affect amplifier linearity and change in impedance at
the Drain(s)?
73.......Steve Smith WB6TNL
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Re: DSB transceiver heat sink
chuck adams via groups.io "The QRPGuys new DSB transceiver requires the 3xBS170 FETs
to have some heat sinking. Attached is photo of my solution." Good idea. Does the production board still have the copper fill area next to the FETs as in the photograph? The reason I ask is that the pictorial layout and the instructions (man. 100219.pdf, pgs. 3, 4 & 5) has the FETs mounted vertical . "So I'd recommend a 22V zener or higher at 1W rating across the PAs."
I too noticed the lack of a protection Zener. This bears some experimentation, IMO. I'm wondering how the added capacitance from the Zener might affect amplifier linearity and change in impedance at the Drain(s)? 73.......Steve Smith WB6TNL
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DSB transceiver heat sink
The QRPGuys new DSB transceiver requires the 3xBS170 FETs
to have some heat sinking.
Attached is photo of my solution. I used some 7mm wide
heat sink tape that I bought off of ebay for cheap that
came in a 10m or larger length roll. I use it for heat
sinks that come without the tape for CPUs.
Allows heat sinking and allows replacement if ever needed.
I find it much easier than using wire and/or aluminum strips
with screws for hold downs.
I,too, dislike with a passion the use of 3xBS170 FETs for
finals. The first time you transmit without an antenna
connected, have a high SWR or have a short at the BNC or
later, you will blow the finals. I know that Steve Weber
loves to use these puppies because they are so cheap, but
it is such a hassle to replace them. The DSB xcvr as it
is now has no zener protection, but you could easily
solder a zener in place beneath the board.
Ken shows 4W out on 40m. That means a peak voltage of
20V. So I'd recommend a 22V zener or higher at 1W rating
across the PAs. You know the drill.
I think that someone may have mentioned the use of the
2.54mm headers like Diz used in the 5W for use on the
PAs and this will allow replacement without having to
get the soldering iron out.
Some one come up with a replacement transistor. You have
to have done it, none of the 'I think this will work' to
lead us off into the weeds. TIA.
FYI
chuck, k7qo, trouble maker
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Randy.AB9GO
