Well, pushing the limits on the irf510 mosfets, they caved on me. So, digging through my junk I found four irfp260's and soldered them in as an effort to get back on the air. So far, it seems to work, but I noticed the current draw is much lower and a bit more heat is created, however, I have pretty get distance on wspr and about the same reports on ft8.

Does anyone know if there are any changes that should be made to the ubitx to get it to work better (with more output) using these mosfets? The obvious answer is to order some more irf510's from jameco and put them in, and quit limping the radio along on these other mosfets...but..ya know, spare parts bin and all.
--
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N5WLF, Greggory (or my nickname, Ghericoan)
General Class, Digital Radio Hobbyist

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Some of these clones seem to blow for no particular reason.
I think we primarily must limit the supply voltage, not so much the current under load.

Though they are really good at dealing with variations in supply voltage.
The series resistor in the 12v supply could be a solution for a good (non WX)?TDA2822
if you are worried about exceeding the max power dissipation spec at high volume
and low load impedance.

开云体育

The DPAK package is perfect.?

Quiescent current into the TDA2822 is around 6ma, peaks can be 1 Amp.
Though?100ma might be sufficient for moderate speaker volumes.
You would need two resistors for a voltage divider, and maybe waste 500 ma through them
to keep the voltage moderately well regulated.

Good spot for an LM7805.

Regarding Joe's suggestion of using the Raduino's LM7805 to power the TDA2822:

One objection I would have is the extra wire, needs to be dealt with every time?
I unplug the Raduino.? Though not a big deal.
A spare LM7805 on the bottom of the main board is more convenient.

A 25 ohm 1/2 watt resistor in series with the 12v Vin lead of the Raduino's LM7805?
should solve the problem with extra heat.? And/or a heatsink on that LM7805.
Add caps to ground on both ends of the resistor to kill any tuning clicks.
I would think those caps could be fairly small, but some here report success using
electrolytic caps of several hundred uF's.? I haven't bothered, no clicks.

Adding that wire for a regulated 5v from the Raduino adds opportunities for
Nano clock noise to get into the receiver.? Keep it short, put a 0.01uF cap at each end.

Can't use the 78L05 that gives the IRF510's their gate bias,
because that regulator must be shut down during receive.

Jerry

Jerry,

I'm not sure everyone understands what foldback current limiting
is. Your message 40729 explains it well. In action it is like a fuse.
The power supply opens the power lead until the operator takes an
action.

It is not the same thing as current limiting.

I don't have any power supplies with foldback current limiting so for
me a fuse is the next best thing.

tim ab0wr

On Thu, 15 Mar 2018 16:46:37 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

True.? The standard current limiting supply I described is not
something to lean on to avoid driving the final too hard, that's not
what I was suggesting. If there's a current limit on the finals,
should be foldback current limiting:
/g/BITX20/message/40719

IRF510 and IRF512 both have a Vds max of 100v.
According to these guys, at least, not many IRF512 datasheets out there:
? ??
The IRF510 has a slightly lower forward on resistance, slightly higher max drain current.
So seems to be a win for the more common IRF510.

Though the IRF512 does have a slightly lower reverse voltage drop, I'll give it that.
Useful when using the FET as a freewheeling diode on a switching power supply,
but not of much interest to us until we reverse the PA-PWR supply leads.


BUZ20 has an input capacitance of 1500pf vs 180pf on the IRF510.
IRFZ10 has a gate capacitance of? 300pf,? Vds max of 60, though can handle more drain current.

There are reasons the $0.50 IRF510 (in hundreds, Vishay, from Mouser) is so popular for HF amps.
Does seem to take something more than a few 2n3904's to drive it properly at 30mhz.

Jerry

It might be worth looking for some auctions as well. I've never understood how I did anything with solder before my metcal sp-200 iron I've had for 20 yrs now. It's way more iron than I need and bought it originally to do surface mount components.? It's near instant heat through high-frequency and will adjust based off of thermal demand.??

I did a quick search at my local "toy store" here in town but I'm not sure where you're located so it might be more trouble than it's worth.... They do ebay auctions from their physical location and have quite often had soldering irons roll through. I'm not affiliated with them but do give them business whenever I can? - ?That's the same SP-200 model I have and they still have plenty of tips available on the market.? I'd definitely buy one again if the one I have dies.? Average used going price for them outright is around $100 USD. I can see if they'd let me test that one if you'd like since they're about 10 minutes from my house.

Look at the types of soldering you are going to do and match the capabilities of the iron to the work. The one above can go from SMTs to soldering a battery cable with the appropriate tips.? If you're just going to do the occasional soldering, get something with high ratings and enough power to handle what you'd anticipate if you pick up other projects.??

Drew - KB1JPW

True.? The standard current limiting supply I described is not something to lean on
to avoid driving the final too hard, that's not what I was suggesting.
If there's a current limit on the finals, should be foldback current limiting:?
? ??/g/BITX20/message/40719

A polyswitch does much the same thing very cheaply,
though the trip point is not quite so well defined.
? ??/g/BITX20/message/19867


I have an old bench supply I found at Goodwill, has voltage and max current adjust knobs.
Very useful when first powering up a new design.
Also useful for things like checking a zener or charging a battery, use it all the time.

Weird that none of the cheap switchers provide either flavor of current limit.
Ideally both, strap selectable.

Jerry

Could work, first time this was suggested.
An extra wire, the Raduino regulator would get hotter.
?

开云体育

Title. Fake news.?

--

Actually, the closest available MOSET to the IRF510
is the IRF512, which is the same device, only it is rated
for a drain voltage of 100v. It goes by other numbers as well.

There are many devices which are on a par with the IRF510.
such as the IRFZ10 and the BUZ20. Fairchild is a major
manufacturer. Try looking for MOSFETS with about the same
drain voltage or better, low R(ds) on, and relatively low gate
capacitance. It is the gate capacitance which makes the
real difference for a multi-band device. The IARF520 is ok;
it can be adapted; but there are others which are better.

Mind you, none of these include any RF devices. The real
reason they are used is because they can be adapted to RF,
and they are much cheaper than the RD16XXXX devices.

AFAIK, most of the RD05/15/16XXXX devices are still being
made, and the Hitachi devices are still readily available. That
may change tomorrow...

john
AD5YE

When you current limit the PA you are doing the same thing that happens
when you overdrive a linear amp and cause flat-topping, i.e. the PA is
driven out of its linear range.

That causes spurious products in your transmitted signal.

You would be better off fusing your PA so it can't pull too much
current. Then adjust your drive level so the fuse never blows.

tim ab0wr

On Wed, 14 Mar 2018 15:15:40 -0700
"Walter" <W9KJO@...> wrote:

On Wed, Mar 14, 2018 at 01:28 pm, Jerry Gaffke wrote:

Had never heard of Drok, they have lots of stuff up on Amazon.
Does your Drok allow you to set the max current anywhere from 0
Amps to say 5 Amps?
Sorely needed.

Lots of cheap switchers out there now, but none of them seem to deal
properly with current limiting.
Should be able to set both the regulated voltage and the max
current. If the load sucks too much current, the voltage drops
until the current comes within the set limit.

Any of those switchers could do this for the price of an op-amp and
a pot, maybe an extra $1.

Jerry, KE7ER
?

On Wed, Mar 14, 2018 at 12:47 pm, Walter wrote:

A little more expensive model put out by droke even has a current
limiting feature.

Well, I had not thought about the current limit.

I installed one for the PA voltage that does not have the current
limit feature.? I will change it out to the current limit model and
use the voltage only for the board supply.

Now I just need to figure out how to adjust the current limit.? I
think a resister network to draw current while I adjust it to the
desired current level.? That would be a great safety feature.

Anyone have an idea about what the max safe current for the PA buss
would be??

--
73, W9KJO
Walter

开云体育

Jerry has the group discussed pulling 5v from somewhere else like use the 5v that powers the Raduino? Maybe temporarily until they can get a regulator and or new WX chip??

Jerry,

A lucid and easy to follow explanation! Thank you!

tim ab0wr

On Wed, 14 Mar 2018 10:59:28 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

Here's a current and more complete summary of what's going on with
the uBitx. For the few who really really want to know.
Not many, judging from the response to post 44278.

Actual frequencies used in the original uBitx code are to have clk0
(bfo) fixed at 11996500 hz, maybe 500hz below the 12mhz filter's 2000
hz wide 3dB passband. Oscillator clk1 (second local oscillator) is
fixed at 56995000 hz for USB and 32995000 hz for LSB. You can find
those three numbers in file ubitx_20.ino at lines 166, 163, 164
respectively. I'm looking at the version dated Dec 6, 2017:
??

The vfo is used to select the operating frequency Fop according to
these formulas. For USB:? ? Fop? = vfo - (clk1-bfo)? ? ? ?so? ? vfo =
Fop + (clk1-bfo)? ? ? ?where clk1 is around 45mhz+12mhz For LSB:
Fop? = vfo - (clk1+bfo)? ? ? ?so? ? vfo = Fop + (clk1+bfo)? ? ? where
clk1 is around 45mhz-12mhz

To receive a 7.2mhz LSB signal (where 7.2mhz is the frequency of the
suppressed carrier), the VFO gets set to
?7200000+(32995000+11996500) = 52191500 hz. That formula gives an
exact result, not an approximation.

Regarding USB vs LSB:
The BFO corresponds to the carrier frequency of the station being
received or transmitted. The 12mhz filter is always above the BFO, so
within the 12mhz IF it allows through only the upper sideband. The
VFO is always above the 45mhz first intermediate frequency, and so
always inverts the sidebands: A carrier at 7200000 would get
translated to vfo-Fop = 52191500 - 7200000 = 44991500 hz A lower
sideband at 7198500 would get translated to 52191500 - 7198500 =
44993000 hz

In this example we assume the lower sideband is generated from a
single audio tone into the mike of 1500 hz. I have chosen 1500 hz
because it will land in the middle of the 12mhz filter's
passband,?assuming the filter has a 3 dB passband that's 2000 hz wide
and the BFO is 500 hz below that passband. The actual range of
frequencies passed will be 500 to 2500 hz. Those assumptions of 2000
hz and 500 hz might be off by a couple hundred hz.

Likewise, a high side clk1 of 56995000 hz? for USB always flips the
sidebands when translating to 12mhz, however the low side clk1 of
32995000 hz we use to receive the 7.2mhz LSB signal does not: Our
7.2mhz carrier:? ? 44991500 - 32995000 =? 11996500 hz? ? (exactly
equal to our BFO frequency) Our 7.2mhz lower sideband:? 44993000 -
32995000 = 11998000 hz? (in the middle of the crystal filter passband)

That's how the original uBitx code works.
I believe there is a problem because where an LSB signal hits the
45mhz filter will be 4khz removed from where a USB signal hits it,
resulting in a different audio quality between the two. A solution to
this is found in post 44278, review the previous posts in that thread
to see why. Even with the fix, there will be differences in the audio
unless the 45mhz filter response is flat across the 2000 hz at the
center.

Jerry, KE7ER

On Wed, Mar 14, 2018 at 09:07 am, Michael Shreeve wrote:

Thankyou Jerry for trying and fairly successfully explaining what
Ashhar is doing by using the ACTUAL frequencies used in the uBITX.

I used to watch my grandfather repair tube TV’s with this one.

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