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uBITX - Sensible mods
#ubitx
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Nigel G4ZAL
Having ordered a uBITX and await it's delivery sometime in the new year, I'm wondering what our most learned would consider 'sensible' mod(s) to enhance the uBITX, or should I just use it 'as is' ?
In the first instance, I will get it up and running as supplied before undertaking any mods so as to establish a base line to work from. This will be my first bitx kit and having trawled some of the posts here, I'm left a little confused as all the bitx posts are in one place and not only for the new uBITX. There's nothing much on t'internet yet either for the uBITX, so maybe this post could be useful to me and others? Nigel - G4ZAL |
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Hi Nigel.
You will be amazed at it performance. Hang in there as 2018 is but days away. If you check the uBitx page under "hacks" you will see three posts from me. One covers how to add a linear amplifier control that is interfaced?to the PTT --this works for SSB only as CW uses a different method for TR. Using two external amps I can compete with the Kalifornia Killowatts out here in the left coast using the uBitx as the exciter. The second involves using a fast blow fuse in the line cord since there is no foldback current protection on the IRF510's. This is most useful when loading the uBitx into an antenna tuner (non-auto tune). Third, in my build I remote mounted the LCD to the front panel using 4 inch long MF jumpers (you will need 16 of them). These are available from All Electronics. While you are at it ditch the "seasick" green background LCD and install a cool blue LCD with white lettering. Much Better! I have posted two you tube videos (search under N6QW) and you will see the build and the blue/white LCD. If you plan to use a metal case and want to cut a clean hole, use masking tape to outline the hole and that protects the case from misplaced file marks and gives the outline of the perfect hole. Have operated the uBitx stock (no amps) on 40/20M and it does a FB job barefoot. I too had some difficulty initially getting it to work on SSB. You must use the supplied microphone button and VU2ESE used the convention of the tip being the microphone input. All my mic bodies are wired with the Tip = PTT, Ring = Microphone and Sleeve = Ground. Once I changed those two items we had fire in the wire. 73's Pete N6QW |
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On Wed, Dec 27, 2017 at 08:45 pm, <N6QWHAM@...> wrote:
The second involves using a fast blow fuse in the line cord since there is no foldback current protection on the IRF510's. This is most useful when loading the uBitx into an antenna tuner (non-auto tune).Wait, what?? Haha, I thought all that fuss was about making sure the power supply wasn't plugged in the wrong way!? Do I need to pay closer attention to this? |
开云体育Hi Arvo,
?
I literally “tripped over” this issue. I was attempting to load up my 3/2
wavelength 20 Meter dipole on 75 meters using a manual auto tuner. Although the
uBitx came supplied with a power plug, my? Bitx40 kit had a power plug and
in line fuse holder. In my desire to quickly get the uBitx on the air –I simply
used the power cord from the Bitx40. I don’t often operate 75 Meters so while in
the CW mode (key down) I attempted to tune the antenna tuner. It was taking some
time when all of a sudden the rig went dead off.
?
We all know that sinking feeling of just having smoked the rig. So the
first thing I do is to check the fuse – and sure enough it was blown. I then did
a bit of thinking about why the fuse would blow. It was not having the wiring
reversed but that I exceeded the current rating of the fuse (2 amp). So then I
looked at the uBitx power amp circuitry. This is not a failure of the design but
purely that in many rigs there is an internal SWR sensing circuit and when it
exceeds some value such as 3:1 there is circuitry to reduce the drive (and power
output of the final stage and less current draw).
?
A new fuse confirmed the rig was not smoked and tuning into a dummy load
confirmed the finals were OK. So by using the power cord from the Bitx40
actually saved the day (and the finals)? and thus the suggestion of
installing an in line fast blow fuse to protect the finals when there is high
SWR which would lead to a higher than normal current draw. Depending on how you
operate and your individual rig, a 2 amp fuse may give you nuisance tripping so
you may have to upsize to a 2.5 amp fuse. The fuse also works with the reverse
voltage protection.
?
Yes closer attention is recommended.
?
73’蝉
Pete N6QW
? Sent: Thursday, December 28, 2017 7:04 AM
Subject: Re: [BITX20] uBITX - Sensible mods #ubitx ?
On
Wed, Dec 27, 2017 at 08:45 pm, <N6QWHAM@...> wrote: The second involves using a fast blow fuse in the line cord since there is no foldback current protection on the IRF510's. This is most useful when loading the uBitx into an antenna tuner (non-auto tune).Wait, what?? Haha, I thought all that fuss was about making sure the power supply wasn't plugged in the wrong way!? Do I need to pay closer attention to this? |
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Holy smokes!
I'm a bit too new at this to "know that sinking feeling of just having smoked the rig." Also, there was a thread about the BITX40 that suggested it was pretty much bulletproof to high SWRs. /g/BITX20/topic/6065942 So I was not thinking about excessive SWR potential for damaging the ?BITX. I am now. Thanks for the explanation! |
开云体育Hi Arvo,
?
Actually I hate to post to these reflectors as you will get a variety of
responses that say well that never happened to me!
?
I can only share that the fuse went up in smoke and that my assessment was
high current draw. So a fuse and fuse holder despite what the radio illuminati
will tell you is cheap insurance when “bullet proof” is not good enough.?
But it was something that I used accidently and the current draw did
exceed? 2 amps and my conclusion was high SWR. I am keeping that power cord
and fuse in my installation.
?
So you decide.
?
Pete N6QW
? Sent: Thursday, December 28, 2017 7:52 AM
Subject: Re: [BITX20] uBITX - Sensible mods #ubitx ?
Holy
smokes! I'm a bit too new at this to "know that sinking feeling of just having smoked the rig." Also, there was a thread about the BITX40 that suggested it was pretty much bulletproof to high SWRs. /g/BITX20/topic/6065942 So I was not thinking about excessive SWR potential for damaging the ?BITX. I am now. Thanks for the explanation! |
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Vince Vielhaber
According to the Tune-up instructions, the uB idles in SSB at 700ma. The B40 drew an amp in SSB with a loud HALLOW. It's not inconceivable that the uB would draw 2A or maybe more in CW.
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Vince. On 12/28/2017 11:05 AM, N6QWHAM@... wrote:
Hi Arvo, --
Michigan VHF Corp. |
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Keep in mind the fuse blew because I was Key Down in the CW mode trying to tune an antenna tuner with an antenna that was presenting an high SWR! The current draw exceeded 2 amps.
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Under normal conditions with a tuned antenna and normal CW keying very likely the draw would be a lot less than 2 amps and the fuse would not blow. It is the aberrant condition when you have the uBitx "key down" for long periods of time (in excess of say 30 seconds) and the SWR is off the chart that the fuse will provide some protection to the finals. That is the essence of what was being said and the reason for the fuse protection. Pete N6QW -----Original Message-----
From: Vince Vielhaber Sent: Thursday, December 28, 2017 8:10 AM To: [email protected] Subject: Re: [BITX20] uBITX - Sensible mods #ubitx According to the Tune-up instructions, the uB idles in SSB at 700ma. The B40 drew an amp in SSB with a loud HALLOW. It's not inconceivable that the uB would draw 2A or maybe more in CW. Vince. On 12/28/2017 11:05 AM, N6QWHAM@... wrote: Hi Arvo,-- Michigan VHF Corp. |
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The IRF510's are good to 100v from drain to source, which is pretty good.
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In that old thread, Allison is quoted as saying heat is what mostly kills those IRF510's if the design of the amplifier is solid.? (An example of poor design is driving the gates with too high an impedance, allowing Vgs to exceed its max rating due to capacitance between gate and drain.)? Allison has?had little trouble when occasionally driving badly mismatched loads even when using a 28v supply. Yes, the IRF510's can blow if a mismatched load causes excessive current draw. But the failure mechanism will likely be due to the IRF510 die getting too hot. A fuse on the IRF510 supply and a good heatsink is probably sufficient protection. I'd occasionally check the IRF510 tabs to see if they are getting uncomfortably hot? when first operating continuously in some digital mode at high power, for example. Jerry On Thu, Dec 28, 2017 at 07:52 am, Arvo KD9HLC wrote: Also, there was a thread about the BITX40 that suggested it was pretty much bulletproof to high SWRs. |
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Rahul Srivastava
Over the years I have seen the love hate relationship with IRF510, it has been used and abused in CB, KPA100 amps of Elecraft right down to Ubitx. Everyone grumbles about the high gate capacitance ... well FETs are akin to valve how about using them in in grounded gate configuration the gate capacitance goes to ground understandably the over all gain would be slightly low something akin to 10 dbs per stage but on other hand it will work with some good gain upto higher freq range. A? thought 73 Rahul VU3WJM? |
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Vince Vielhaber
Go here:
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You can get both 2 and 4 line displays. No relationship to the company, just a recurring customer. Vince. On 12/28/2017 03:10 PM, Arvo KD9HLC via Groups.Io wrote:
On Wed, Dec 27, 2017 at 08:45 pm, <N6QWHAM@...> wrote: --
Michigan VHF Corp. |
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M Garza
Would grounded gate work for SSB? Marco - KG5PRT? On Dec 28, 2017 2:54 PM, "Rahul Srivastava via Groups.Io" <vu3wjm=[email protected]> wrote:
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Marco KG5PRT and Rahul VU3WJM Grounded Gate with a pair of IRF510's in push-pull configuration is interesting.? I may have to try it sometime.? In tube technology the grid is placed between cathode and plate but in MOSFETs the gate varies apparent resistance between source and drain.? I don't clearly understand the subtle differences.? Grounded gate operation is routinely used with J-FETs as small signal amplifiers, but I could not find any on-line examples of similar operation with power MOSFETs. Is there a particular reason that apparently nobody uses power MOSFETs in common- gate configuration? Arv? K7HKL On Thu, Dec 28, 2017 at 2:54 PM, M Garza <mgarza896@...> wrote:
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A "grounded gate" of what, Marco?
Not of the IRF510 or any other MOSFET. The current through the device is determined by the gate voltage. with a gate at 0v, the current through the device is virtually 100% cut off. There is no way to get a signal through it. The gate voltage should be about 3v for signal transfer. However, it inherently has a high gate capacitance which has to be compensated for at the frequency of interest. That high capacitance comes from the bigger than averabe size of the die, which is really designed a lot of current flow in a short period of time (usecs). Operating it linearly means that we are trying to make it pass a relatively small amount of current (~1-2A) over a relatively long period of time. The die heats up because of the current flow, and that has to be controlled. So there are two problems: we must make a reasonable impedance match to the gate to allow signal transfer, and we must control the inevitable heat generation from that. Heat-sinks control the latter. What would you do about the former, i.e., how would you match the driver transistor to the gate with high capacitance at 40m (or whatever band you choose)? There is one other problem. The MOSFETS are inherently prone to oscillation because of internal feedback. Often, it is VHF oscillation and is more or less invisible to the operator. That must also be controlled. That is both a drive and a layout problem. john AD5YE |
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John? AD5YE I understand that some people take "Grounded Grid" and "Grounded Gate" literally, but the Grid or gate could be at ground for RF but not for DC bias.? That is common in several Ground Grid amplifier designs.? The capacitance issues are something I don't totally understand. Arv? K7HKL On Thu, Dec 28, 2017 at 4:06 PM, John Backo <jabac@...> wrote: A "grounded gate" of what, Marco? |
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Gordon Gibby
开云体育?In grounded grid (or gate) configuration, I believe all you may expect is basically VOLTAGE GAIN.? ?if yoiu have a 50 ohm input impedance and you are feeding the cathode (or source) then your driving RF current is the same as the drain / plate current ---
the gain coming from the drain/gate being at much higher voltage than the input.? Essentially a higher impedance.
With a tube amplifier, that plate dc voltage might be 2000 volts or more ---- rather impressive voltage gain is possible under those circumstances.? ?
Of course with a MOSFET you are probably more like 100 volts max....or less....so maybe the possible power level in one device is lower and not sure about the possible gain?? ?
Gordon
From: [email protected] <[email protected]> on behalf of Arv Evans <arvid.evans@...>
Sent: Thursday, December 28, 2017 6:00 PM To: [email protected] Subject: Re: [BITX20] uBITX - Sensible mods ?
Marco KG5PRT and Rahul VU3WJM
Grounded Gate with a pair of IRF510's in push-pull configuration is interesting.? I may
have to try it sometime.? In tube technology the grid is placed between cathode and plate
but in MOSFETs the gate varies apparent resistance between source and drain.?
I don't clearly understand the subtle differences.?
Grounded gate operation is routinely used with J-FETs as small signal amplifiers, but I
could not find any on-line examples of similar operation with power MOSFETs.
Is there a particular reason that apparently nobody uses power MOSFETs in common-
gate configuration?
Arv? K7HKL
On Thu, Dec 28, 2017 at 2:54 PM, M Garza
<mgarza896@...> wrote:
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Gordon Gibby
开云体育?Another person asked about SSB --- yes, grounded grid (and gate) should be usable for SSB.? ? Nothing changes about the linearity (or lack of) in the device --- just the input impedance presented to the exciter changes.
gordon
From: [email protected] <[email protected]> on behalf of Gordon Gibby <ggibby@...>
Sent: Thursday, December 28, 2017 6:22 PM To: [email protected] Subject: Re: [BITX20] uBITX - Sensible mods ?
?In grounded grid (or gate) configuration, I believe all you may expect is basically VOLTAGE GAIN.? ?if yoiu have a 50 ohm input impedance and you are feeding the cathode (or source) then your driving RF current is the same as the drain / plate current ---
the gain coming from the drain/gate being at much higher voltage than the input.? Essentially a higher impedance.
With a tube amplifier, that plate dc voltage might be 2000 volts or more ---- rather impressive voltage gain is possible under those circumstances.? ?
Of course with a MOSFET you are probably more like 100 volts max....or less....so maybe the possible power level in one device is lower and not sure about the possible gain?? ?
Gordon
From: [email protected] <[email protected]> on behalf of Arv Evans <arvid.evans@...>
Sent: Thursday, December 28, 2017 6:00 PM To: [email protected] Subject: Re: [BITX20] uBITX - Sensible mods ?
Marco KG5PRT and Rahul VU3WJM
Grounded Gate with a pair of IRF510's in push-pull configuration is interesting.? I may
have to try it sometime.? In tube technology the grid is placed between cathode and plate
but in MOSFETs the gate varies apparent resistance between source and drain.?
I don't clearly understand the subtle differences.?
Grounded gate operation is routinely used with J-FETs as small signal amplifiers, but I
could not find any on-line examples of similar operation with power MOSFETs.
Is there a particular reason that apparently nobody uses power MOSFETs in common-
gate configuration?
Arv? K7HKL
On Thu, Dec 28, 2017 at 2:54 PM, M Garza
<mgarza896@...> wrote:
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Arvo W0VRA
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