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On Sun, Sep 23, 2018 at 09:53 AM, KM4TRT wrote:

) I get about 90 mv @ 45 MHZ just before the crystal filter with the amount of hash you'd expect to see after a mixer
4) Nothing out of the crystal filter. or out of the second amp.
Yes I did check voltages on all the concerned transistors
Can I use any of the cheap bandpass filters from Ebay as long as they are +/- 7.5 Khz pass

The second amp is at ~12mhz.? if the LO to the second mixer is not correct then nothing works.
The second LO is in either 33 or 57 mhz (check the docs).

The chain from antenna in is 14.0mhz upconverted to 44.985ish mhz and then down converted to 12mhz.
If any of the oscillators are wrong you miss the 45mhz pass band or the 12mhz filter pass band
(11.995 to about 12mhz) you get nothing as in deaf.

Those 45mhz filters are not likely to fail, bad joints are possible. Any? 45mhz filter should work 7.5 or the
wider 15Khz.? ?

I'd insure that the calibration went well and the 3 digital oscillators are indeed where they should be.
IF they are not its? going to be a deaf rock.

Allison

Henning,

Just one more part of the picture but less an issue for lower power.
I call that saturation thought its something different.? To many I call that the
hockey stick region as it really bends sharply.

The problem is at 12V you get distortion under about 2V and hit the wall at 12V.
To get power you want to vary current to the load without hitting either?you need
a minimum of about 2A into not 50 ohms but about 10-12ohms?to do that.

I look at the uBitx and the 1:1 output transformer just cannot do that.
IT is also why besides all other problems the IMD goes bad at about 2W.
Lower the load or raise the voltage(to about 24V) and at least 80m
things improve greatly.

Whats interesting is others have seen and applied this with good result.
As I have three such examples.

Allison

After hooking up my new Nextion screen and making several great contacts, I was trying to optimize the frequency calibration and? hit the PPT switch a few times with the antenna switch in the wrong position.
I get no signal on receive or transmit.
I believe I tracked the problem down to the 45 MHz bandpass filter because:
1) I injected a 14.725 signal at 100mv at the antenna.
2) I tracked it through the first filter and the the first mixer and amp( on the scope) and
3) I get about 90 mv @ 45 MHZ just before the crystal filter with the amount of hash you'd expect to see after a mixer
4) Nothing out of the crystal filter. or out of the second amp.
Yes I did check voltages on all the concerned transistors
Can I use any of the cheap bandpass filters from Ebay as long as they are +/- 7.5 Khz pass

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR0.TRC0.A0.H0.X45+mhz+bandpass+filter.TRS1&_nkw=45+mhz+bandpass+filter&_sacat=0

I looked up the WTL filters and don't see the Z 7? thats stamped on mine.
The WTL spec sheet has a 2 pole or 4 pole 45/3OT or a 2 pole of 4 pole 45/fundamental.
http://www.wtlcrystals.com/UploadFiles/31.jpg
Anyone familiar? with this?
Thanks-Andy KM4TRT

开云体育

Allison,

one more point: for the load always stay off the "knee" i.e. the so called ohmic range. Above this point the MOSFET acts like a voltage controlled (control voltage is the gate to source voltage) current source.

Example: for VGS = 5 V stay awav from the range of VDS = 0 to about 1 V. As easily be seen the "knee" gets worse for higher drain currents.

A similar condition happens for the RD16HFF1, having a larger ohmic region--? and in addition a limited maximum drain source voltage. The IRF 510 can do better as it can be operated at higher drain -source voltages.

The result: as the maximum drain -source voltage swing for the RF signal is limited the maximum output power can be only achieved through the output transformer and its transformation value.

There is a good explanation of this relationship in the proceedings of the "UKW-Tagung Weinheim" a few years ago by the author Prof. Dr Jochen Jirmann DB1NV.

? Henning Weddig

DK5LV?

Right now we are in a low time of sunspots which is part of the Solar Flux equation that effects our Ionosphere and allows the upper HF bands to work (20 through 10 meters) Until the Solar Cycle starts to raise again, 20 and up will be spotty in whether it's open or not.

Hello, I upgraded to the KD8CEC firmware last night and I really like it. I see that there is also the uBitx Manager software.?

Im guessing that I can backup my existing settings with this software? ?I’ve been trying to get everything dialed in as far as the BFO and the calibration settings go and occasionally I really get things whacked out. It would be nice if the manager software allows me to back things up and then restore it to a good point should I mess things up.?

Is that that one of the uses of the Manager Software? ?Also, do I use the Manager software with the radio powered up with the 12v power supply or only by having the USB cable attached like when you program the radio?

Thanks,

Curt

Perfect!? Thanks Allison!? I'm doin it!

Daniel,

I'm a bit of a noob, but I have been playing with with various transceivers in receive mode for a few years.? For what it's worth, I can tell you that regardless of the unit, your going to need more antenna to get decent reception.? Even if it's just taped to the ceiling where you live.? Up in a tree is better.? If it's for receiving only, you can use any cheap wire of any size.? Short antenna and bad band conditions = no reception.

Do this and I think you'll be pleased.

Air core has one liability that is mutual coupling.

So if you use air core the parts must be oriented so they will not couple
That means one in each plane of X, Y and Z.? Supporting the Z might be?
annoying (coil spirals away from the board).

Air core want to be no less than 1 coil diameter from any metallic surface
or wall. The rule of thumb for good Q is three coil diameters.

That and they will be bulky.? Wire size for 10W is anything you can
make mechanically stiff for self supporting and at least #28 for wound
on former.? Heavier gauge wire is handy for that.

For this close wound is likely ok.? Note higher Q may impact filter characteristics.
?
Allison

I'd like to build a few lpfs for my ubitx.? Can I use air core inductors?? I've got plenty of magnet wire and there are lots of inductor calculator online.

If this is doable,? Is close wound ok?? Also, what effect would wire size have?

Thanks in advance.

Tim,
IMD can be caused by two things, saturation at high power and
cross-over distortion near idle conditions.

You missed one.? Anytime the output is not a uniform multiple of the input.
Or what is know ans non linear behavior.

Good example the HFE of 3904 at 10ma is 100, at 100ma its 40.? So is the?
waveform causes it to swing from 10 to 100ma the gain supplied is varying.
The base current required to get 10ma and 100 ma is not ten times higher
it is more like 25 times higher and the change is varying for intermediate
currents.??

For power MOSfets this is pronounced at low gate voltages as first we have
threshold where below that there is no conduction. as we go up from that point
the curve is markedly curved then straightens and at some high current bends
again.

For information look at the Ids VS Vds for Vgs curves.? From that graph we can get a
load line that reflects input voltage.? Old tube hands likely the curves looking like?
many power tubes.? ?It is on the page upper right corner.? Do not let pulsed be a bother
as in some cases those curves represent power well above what the device can do
sustained.? Needless to say its hard to run the drain to zero volts and remain linear.?
It also indicates a Gm of about 1S? IE 1Vgs change causes a 1A Drain current change.

Allison

Hey everyone! I have a uBitx for few days and I can say that it's awesome! it's my first and only HF transceiver. Yesterday I listened all across 10m to 80m with just few meters of copper wire as an antenna. I can say that was... radio silence almost all over except for the 40m band. Now that I can see 40m band as a quite crowded place, I'm wondering... is there any advantage of having a Bitx40 comparing to uBitx? Is the reception or the transmission of the smaller brother somehow better comparing to the other one, giving the fact that Bitx40 is focused for 40m band only? Because now I'm wondering maybe uBitx wasn't the right choice for me and I should opt out for Bitx40. If we speak only about 40m band, can we say that Bitx40 is better than uBitx or not ? Thanks, and I strongly appreciate any kind of information and comment.

Jim,

Its not only if you do not meet "x" your problems start earlier.
Its the difference between ON and "well sorta on" the latter being conducting but not hard..
For commutating mixers (DBMs and other ) just sorta conducting is not on or off and
non-linearity is then the problem.

In the end not enough means exactly that.

Allison

IMD can be caused by two things, saturation at high power and
cross-over distortion near idle conditions.

I suspect the high standing current prevents cross-over distortion
which is why you get better IMD performance.

tim ab0wr

On Sun, 23 Sep 2018 14:53:53 +0400
"Ashhar Farhan" <farhanbox@...> wrote:

Allison,
Modelling confirmed to me that fewer active devices (and hence higher
gain per stage), the better is the IMD. From an IMD perspective,
higher gain with high standing current results in better IMD.
That's why it makes sense to use a VHF power device as
driver/pre-driver block. I did a low distortion (less than - 40dbc
IMD) linear chain a few years ago. At 12v, It had to be an RD16HHF1
device biases for close to class A. At 1A of current, it gave 4 watts
of power. The details are on the emrfd group's file section.
- f

Thanks folks!? I found some good pages on filters to study up on.? Doesn't look too bad.? Think I'll go ahead and build them for the experience points :)

Farhan,

I am very aware that fewer devices are desired for better IMD.? ?The key is using
competent devices at attainable gains.? There are two problems with 3904s in that
role, gain compression at higher operating currents and a distinct problem with
delivering the desired gain at higher frequencies.? ?If they cannot produce the
needed gain any feedback required for?supporting input and output impedance
will be unpredictable producing a cascade of performance degradation.? Its not
what you may have built in some prior time as we have many tested that do not.? ?
Its about how to do it at some production level.

First is we do not ask a device to push above it weight class.? 2n3904 is not going
to deliver more than 12DB power gain at 3-30mhz and less than 1db gain flatness.
The power it can produce is not device dissipation its gain at currents higher than?
its peak current gain (about 10mA for HFE peak and HFE is well down at 100mA).
This shows well of a curve tracer.? We would deire for linear use a prt that has a
more or less flat current gain in the operating range.

By measurement we have insufficient drive and gain at frequencies approaching 8mhz.
As a result of those factors the IMD measured is seriously poor above 2W even on bands
where more power can be delivered.? The key here is power with acceptable IMD from
3 to 30mhz not 3 to maybe 10mhz.? ?We cannot do that with devices that incapable of
that for those first three stages.?

Note this is not an IRF510 issue as the driver has failed to deliver adequate drive and
the prior stages requires overdrive to function at all.? That does not help IMD or spurs.

Also bias of 1A for?RD16HHF is not class A above about 3 to maybe 4W and wanders
into AB1 above that power.? ?A pair of IRF510s at 12V can achieve that at about
250ma though at higher voltages can easily surpass that.? In general the RD16HHF is
about $4.50 more expensive to get maybe 3db better IMD at 12V if everything
around it supports that.? To do that prior stages have to built to do that.? The IK4AUY
amp (IRF510 pp driving IRF510PP) supports the ability of the part to perform.

In either case loading a IRF510 or RD15HHF to 50 ohms Drain to Drain is far too high
a load resistance for more than a few watts.? Reason is MOSFETs are voltage driven
current sources.? ?If you want power from them the load current must swing in the
linear current region without exceeding the available voltage.? So with 50 ohms and
not more voltage say 12V peak 2.88W is about it and we are driving devices to
saturation.? ?We need s a load line what can support a Drain current in the 1-2A region.
for that was need to get to 12.5ohms for a 10W amp without saturating or voltage clipping.
At that point we are running near 1A Peak current and likely with 200-500ma of bias we
are in the linear region for a push pull amp.? Combined with a reasonable feedback for
flatter gain vs frequency the IRF and RD are in the same region.? ?But this will be true
only if the drivers and prior stages are not suspect.

Allison