Date   
Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

Arv Evans
 

John

I occasionally visit Harry's web pages. 
We were both working in Saudi Arabia at the same time but I did not meet him.
I did not find the 10 watt amplifier but did find a few newer entries that were
interesting.

Thanks,

Arv
_._


On Mon, Jan 29, 2018 at 7:10 PM, John Backo <jabac@...> wrote:
For lots of ideas and circuits (including a 7805 push-pull amplifier!)
check out Harry's Homebrew Pages:

http://sm0vpo.altervista.org/index-1.htm

He includes a lot about RF amplifier design and circuits,
including a kind of JBOT mini-linear, and a 10W linear
amp.

It is a very interesting resource.

john
AD5YE




Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

Jerry Gaffke
 

If a fuse is too slow and a simple current limit makes the amp non-linear,
perhaps use foldback current limiting.
If the current ever exceeds perhaps 3 Amps, then shut down the power to the final,
turn on a red idiot light, and latch it up to that state until the operator resets the current limit.
The operator will soon figure out how high to set the mike gain.

This circuit could be entirely contained in the power supply,
no mod to the Bitx40 required to implement this option.
Perhaps combine it with a boost mode switcher to allow higher power operation
from a 12v battery.

I like K9ZC's notion of a hall effect sensor, as that sounds like it should not suffer
the 0.7 volt Vbe drop of Arv's sense resistor.  Lots of other ways to sense current
without introducing a significant voltage drop, some of them cheap.

Jerry



On Mon, Jan 29, 2018 at 05:31 pm, Arv Evans wrote:
his has been an interesting discussion, but still not sure which
might be the best way to insure a long and uneventful life for
MOSFET power amplifiers. 

Re: [SPAM] Re: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

John Backo
 

You are absolutely right, Jerry.

It was not my intent to diss the IRF MOSFETS.
What I am saying is that they are different beasts
and one has to understand that to make them work well.

And it can be done easily enough. Start with the NA5N critique
and the WA2EBY amplifier design article. Follow through
with the notes and comments of KB1GMX. Then one should
have a fair appreciation for what these devices can and cannot
do...and what to avoid.

There is an excellent design of a 300-600W amplifier using the IRF510
in multiples that was built some years ago by the German Radio Club
(among others). These are fantastic designs and worth much study.
Search for them on the web.

john
AD5YE

Re: uBITX Firmware (CEC) 0.30 released (Test version). #ubitx

Ian Lee
 

Philip

Thanks for this firmware. I am borrowing a little memory space left for the next concept and adding fun features.

Ian KD8CEC

2018-01-30 7:36 GMT+09:00 Philip <philip.g7jur@...>:

Hello Ian.
Many thanks for the updated firmware for the uBITX. Makes it much better to tune.
Philip G7JUR



--
Best 73
KD8CEC / Ph.D ian lee
kd8cec@...
www.hamskey.com (my blog)

Re: uBITX Firmware (CEC) 0.30 released (Test version). #ubitx

Ian Lee
 

Joel

You've looked at uBITX Manager. yes i added it at 0.31. for next concepts (with h/w modification)
but, You will soon be able to try out the other of the fun. alwayis info. scroll info.
Now I have added a very small funny feature.

Ian KD8CEC




2018-01-30 2:02 GMT+09:00 M Garza <mgarza896@...>:

Thank you to everyone.
I upgraded to v.31 and set for a straight key.  It is working again.

I see in the new manager an option for a S meter.  What is needed to get that to function?  I hope to have AGC added, tonight, so I could pull the voltage from that and use a 5v zener to prevent over voltage to a pin...

Thank you for all of your hard work and dedication to making this an even better radio!

Marco - KG5PRT 

On Jan 29, 2018 8:44 AM, "Joel Caulkins" <caulktel@...> wrote:
Ian,

I am running .030 also and it works very well. It would be very helpful if there was some documentation to detail the features and how to access them. Thank you for doing this as the uBITX is now more like a real transceiver. 73

Joel
N6ALT



--
Best 73
KD8CEC / Ph.D ian lee
kd8cec@...
www.hamskey.com (my blog)

Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

John Backo
 

For lots of ideas and circuits (including a 7805 push-pull amplifier!)
check out Harry's Homebrew Pages:

http://sm0vpo.altervista.org/index-1.htm

He includes a lot about RF amplifier design and circuits,
including a kind of JBOT mini-linear, and a 10W linear
amp.

It is a very interesting resource.

john
AD5YE

Re: uBITX Firmware (CEC) 0.30 released (Test version). #ubitx

Ian Lee
 

Thanks for information.

So far, what I wanted was a minimal real transceiver function.
Now, before I finish this concept (without h/w modification), I am going to put in one or two fun features (very small) today.

Ian KD8CEC



2018-01-29 23:44 GMT+09:00 Joel Caulkins <caulktel@...>:

Ian,

I am running .030 also and it works very well. It would be very helpful if there was some documentation to detail the features and how to access them. Thank you for doing this as the uBITX is now more like a real transceiver. 73

Joel
N6ALT



--
Best 73
KD8CEC / Ph.D ian lee
kd8cec@...
www.hamskey.com (my blog)

Re: Final schematics for Bitx 40 and uBix?

Jerry Gaffke
 

The schematics on hfsignals for the Bitx40 are final but not necessarily correct.

On the Bitx40, the two modulator diodes D15,D16 plus balancing pot R106 got replaced by a BAT54s dual schottky:
    https://groups.io/g/BITX20/message/33385

All those BC849's?  Have always been MMBT3904's.

L5 and C103 of the BFO are missing, the BFO is at just about the right frequency
if the crystals are matched without any adjustment.  Usually.

L4 in the VFO is not stuffed so the analog VFO doesn't oscillate,  the VFO comes instead from the si5351 PLL chip
on the Raduino through the Bitx40 connector labeled "DDS1" in the schematic.

T6-4 is tied to C142 and R144, U3-3 is tied only to the 12v rail labeled "TX", schematic does not show that clearly.

RV1-2 is not connected to U3, the schematic drawing is just a little tight there.

Otherwise, I think the schematics on hfsignals are correct, reflecting what is currently being shipped.
Nothing has changed in Bitx40v3 boards shipped since Dec of 2016.

But there are a few things that perhaps should change:

D7 and C130 should be across the coil of relay K1,  D8 and C164 are correctly across the coil of K2.

R141 is currently a 1/4 Watt 10 ohm resistor, should be 1/2 Watt as have been reports of it burning out.

The surface mount MMBT3904 at Q13 could be replaced with a through-hole version of the same part, the 2n3904,
as it must dissipate a fair bit of power during transmit.

Even with the radio off but hooked up to an antenna, a nearby QRO transmitter or electrical storm can blow Q13.
Best fix for the Bitx40 is to add a couple back-to-back 1n4148 diodes:
The back-to-back diode mod comes from Raj:   https://groups.io/g/BITX20/message/19105
Note that he suggested adding an incandescent lamp, which can be quite effective:
https://groups.io/g/BITX20/message/21901
Here's a few more notes about what can blow in that transmitter:
https://groups.io/g/BITX20/message/31352

Second harmonic suppression at 14mhz is close to good enough but marginally legal, best to add a 100pf cap across L6.
     http://bitxhacks.blogspot.com/2017/01/nd6ts-suppression-of-pesky-2nd-harmonic.html

Once you get all of that sorted out, you can search the forum for  cures to the ptt pops and carrier bursts and lack of agc
and sometimes insufficient mike gain.  Lots of different methods, I won't pick sides.
Might be worth a thread to hash out best practices to resolve these issues.

Once you have proven the radio to work, you should download Allard's improved Bitx40 code:
    https://github.com/amunters/


I hope that answers your question!   ;-)

Jerry, KE7ER


On Mon, Jan 29, 2018 at 12:42 pm, James Lawrie wrote:
Are the schematics posted on HFSignals the complete final one? Im checking one of my Bitx 40 boards and notice two missing diodes, D16 and D15. 

Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

Arv Evans
 

This has been an interesting discussion, but still not sure which
might be the best way to insure a long and uneventful life for
MOSFET power amplifiers.  Several ideas have been presented
by myself and other individuals.  All seem to have been rejected
by others for various reasons.  Makes me wonder if rejections
are based on reality or just a fear of using any switching device
as an RF amplifier. 

The alternative of using real RF transistors or RF MOSFETs seems
to defeat the objective of designing and building low cost transceiver
from components that can be readily obtained at relatively low cost.

Are the IRF510 failures because they are not suitable for the way
we are attempting to use them, or because we are not being careful
enough in how we use them?  Are IRF510 failures a real problem,
or maybe being exaggerated?  Is there an acceptable way to make
switching MOSFETs more robust in RF applications.

Given the relatively high cost of RF rated devices it may be time to
revisit something like Farhan's JBOT (Just a Bunch Of Transistors)
design to see if that can be scaled up to the 5 to 10 watt range and
cover up to 30 MHz.

Arv  K7HKL
_._




On Mon, Jan 29, 2018 at 4:48 PM, K9HZ <bill@...> wrote:

ALC.  What a ghost from the past.  I’m not aware of anyone who designs RF amplifiers today that thinks ALC is a good idea today specifically it generates nasty products in the PA when it cuts in and makes a linear amplifier…nonlinear.  People used it years ago so that they didn’t over drive (read that blow the grids out of) their tube amplifiers.  Today we use more sophisticated algorithms, head room in over design,  and compression to avoid the issue. 

 

Of course current limited power supplies are not linear RF amplifiers.

 

I think you should present your design, build it, and try it on the air… and have a look through a spectrum analyzer.  Maybe all of the theory I had in graduate school is bunk.

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Arv Evans
Sent: Monday, January 29, 2018 12:49 PM
To: BITX20@groups.io
Subject: [SPAM] Re: [BITX20] IRF510 amplifier failures

 

Maybe part of the point has been missed at several levels.  The proposed current

limiter is not much different from current limiters in many commercial power

supplies.  It is not active until some current value has been reached.  Up to then

there is no current limiting or "modulation" or "compression".  Yes, the in-series

current sensing resistance does allow an output voltage drop until voltage across

this resistance reaches about 0.65 volts to forward bias the sensing transistor.

If your power supply output is not stiff enough to hold a steady voltage this could

add to the sensing resistance and cause voltage droop and in really bad cases
compression of RF output. 

Question...is RF compression all that bad?  It is what most transmit ALC circuits

do.  It would also be possible to make the proposed circuit driven by reflected

power instead of current.  Then we could call it a transmit ALC to protect the

IRF510(s). 

 

It would be fairly simple to add a latching function to the limiter design so that it

totally shuts down output when Imax has been reached.  This is possible but would

then require a RESET button or power cycling to restore power to the RF PA stage.

It is also possible to change the proposed design to put the current sensing ahead

of the control MOSFET and make that MOSFET into a voltage control circuit.  This

was my initial approach but the component count became just too high to be an

internal modification for transceivers.  It would be more suitable for converting

an unregulated power supply to a regulated one. 

 

For those who are using modified PC power supplies it is possible to change the

current sensing so that the switching regulator would shut down if Imax of 2 to 3
amperes is exceeded.  This approach would require power cycling to restore
operation. 

Problem with using fuses is that they have a short but measurable heating period
before they go open.  When they do open they spark internally for another short
period.  Both the delay and the spark are potential problems for circuit components.

Poly-fuse  or resettable fuse devices are intended to address a different issue. 

Some are equivalent of FAST-BLOW fuses, and some are just conventional

resettable circuit breakers.

Suggestion here is that "if you can come up with something else that is adequate,

please submit a circuit drawing and explanation of how it works"  We could all

benefit from that.

Arv  K7HKL
_._

 

On Fri, Jan 26, 2018 at 11:27 AM, Tim Gorman <tgorman2@...> wrote:

A current "limiter" which modulates the current, i.e. limiting the
current no matter the drive level, is like applying an ALC to the
exciter. Improper design can result in compression of the signal which
can then generate spurious responses in the output.

If the current limiter is of a "drop-out" style which requires
resetting then this won't happen, it will just shut down the exciter.
In that case, however, it doesn't provide much efficiency over a plain
old fuse!

tim ab0wr

On Fri, 26 Jan 2018 05:32:08 -0800
"n5ib_2" <n5ib@...> wrote:

> One other possibility to consider to protect against overcurrent
> situations is to use a current limiting power supply, or add a
> current limiter to an existing power supply or battery.
>
> The current limiter circuit whose link is at this site:
> <http://n5ib.net/Index.xht>
> will go up to 2.2 amps, and includes a low-dropout voltage regulator
> that also provides reverse polarity protection.
>
> There is a version, in a different package, of that same regulator
> chip that has an added "tracking" feature - being able to parallel
> multiple chips to increase the available current. Details are on the
> datasheet in the document.
>
> Jim, N5IB
>
>
>



 


Re: [SPAM] Re: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

Jerry Gaffke
 

Yes, an FET built for RF will be somewhat better behaved.
More linear, a wider Vgs active region, less gate capacitance, a tab at ground potential.

But I think Farhan made the right call to use the IRF510 for a $109 ($59 if the Bitx40) radio.
It's popular on amateur transmitters for a reason.  It's very cheap and it can work quite well.
Reread KB1GMX's post:    https://groups.io/g/BITX20/message/22597
and check the web for complaints about the WA2EBY amp:
    http://www.golddredgervideo.com/kc0wox/wa2ebyamp/amppart1.pdf
    http://www.golddredgervideo.com/kc0wox/wa2ebyamp/amppart2.pdf

I doubt most failure modes we see reported here happen in microseconds.
Just be careful with the gate bias control, and use a large enough heatsink to keep the IRF510's cool.
With a proper design, KB1GMX reports most failures are due to too small a heatsink.
If you disagree, go ahead and invest in what you consider a proper FET.
But keep in mind that 99% of the folks reading this forum will stick with the IRF510's.
Yes, the power amp final needs improvement, just like the  ptt pops and lack of agc
and too skinny volume control shaft and flaky CW keying.
A working radio when built as documented on hfsignals.com, but screaming to be tinkered with.
Exactly what I wanted.

Yes, the IRF510 was designed for switching service at much lower frequencies.
So what?  The WA2EBY amp using IRF510's in push-pull works fine across all of HF.

Jerry, KE7ER



On Mon, Jan 29, 2018 at 02:33 pm, John Backo wrote:
I think Sarma is right. The IRFxxx MOSFETS are
really on/off switches. They have a small linear region which
can be used for RF, but they are really designed to be "all on" or "all off".

That means that once they start conducting, they are very fast.
Whatever happens takes microseconds to accomplish. What
device is fast enough to stop that? That is the real question.
And even several amperes over a micro-sized circuit for even a few
microseconds represents a lot of joules of energy...which is why it
is relatively easy to blow up a IRF510. It goes along with the design...

Re: Cheap Harbor Freight Case for MBITX

Michael Hagen
 

The 1800 is now 9.99 with a online coupon.  Great price.

I like the ammo case, probably could put some batteries at the bottom.

Make a front panel sealed under the lid. 

Be great to toss in the car for camping?

73's

Mike, WA6ISP


On 1/29/2018 2:39 PM, Ken Hansen wrote:
This 'pelican-style' case is also nice - I'd love to figure out a front panel that snaps over the bottom half of the case (remove all pick-and-pluck)...

https://m.harborfreight.com/1800-watertight-protective-case-9-316-in-63518.html

Ken, N2VIP

On Jan 29, 2018, at 3:47 PM, wishbone_aaa <dlmock@...> wrote:

Just place my order for a MBITX and have been looking for an enclosure. I spotted in my workshop a Harbor Freight plastic ammo box that looks like it will do the job.  With the lid open, the box is 6 inches deep,9 3/4 wide and 4 1/2inches high.  Price $6.99 (even cheaper when there's a coupon).   <https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore%2Cf%2CEAFeatured+Weight%2Cf%2CSale+Rank%2Cf&q=ammo+box>

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

Re: Second batch of uBITX shipping? #ubitx

James Tate
 

Just to let you all know, I ordered mine in the 4th. When I inquired about status, I did not even get an ETA. I am patiently awaiting confirmation of shipping on a slow boat. LOL  

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Joe Puma
Sent: Monday, January 29, 2018 7:44 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Second batch of uBITX shipping?

 

I ordered one Jan 17th. I recently emailed them and they said it will ship in 2-3 weeks. Glad I ordered DHL. 

 

Sent from my iPhone


On Jan 29, 2018, at 7:37 PM, David Robertson <kd1na363@...> wrote:

Ordered on the 16th and no responce

 

--

Dave Robertson KD1NA

Re: Second batch of uBITX shipping? #ubitx

Thomas Noel <tnoel@...>
 

Y'all are all so spoiled.

I remember ordering from the back of comic books and cereal boxes and having to wait "allow 6-8 weeks for delivery" for my "Amazing X-Ray Glasses" or "Secret Decoder Ring".

No email, no tracking numbers.  Just endless faith and optimism.

And that was just from Kalamazoo  or Battle Creek Michigan.

If you got it at all you were amazed!

Tom

Re: Second batch of uBITX shipping? #ubitx

Joe Puma
 

I ordered one Jan 17th. I recently emailed them and they said it will ship in 2-3 weeks. Glad I ordered DHL. 


Sent from my iPhone

On Jan 29, 2018, at 7:37 PM, David Robertson <kd1na363@...> wrote:

Ordered on the 16th and no responce

--
Dave Robertson KD1NA

Re: Second batch of uBITX shipping? #ubitx

David Robertson <kd1na363@...>
 

Ordered on the 16th and no responce

--
Dave Robertson KD1NA

Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

K9HZ <bill@...>
 

ALC.  What a ghost from the past.  I’m not aware of anyone who designs RF amplifiers today that thinks ALC is a good idea today specifically it generates nasty products in the PA when it cuts in and makes a linear amplifier…nonlinear.  People used it years ago so that they didn’t over drive (read that blow the grids out of) their tube amplifiers.  Today we use more sophisticated algorithms, head room in over design,  and compression to avoid the issue. 

 

Of course current limited power supplies are not linear RF amplifiers.

 

I think you should present your design, build it, and try it on the air… and have a look through a spectrum analyzer.  Maybe all of the theory I had in graduate school is bunk.

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Arv Evans
Sent: Monday, January 29, 2018 12:49 PM
To: BITX20@groups.io
Subject: [SPAM] Re: [BITX20] IRF510 amplifier failures

 

Maybe part of the point has been missed at several levels.  The proposed current

limiter is not much different from current limiters in many commercial power

supplies.  It is not active until some current value has been reached.  Up to then

there is no current limiting or "modulation" or "compression".  Yes, the in-series

current sensing resistance does allow an output voltage drop until voltage across

this resistance reaches about 0.65 volts to forward bias the sensing transistor.

If your power supply output is not stiff enough to hold a steady voltage this could

add to the sensing resistance and cause voltage droop and in really bad cases
compression of RF output. 

Question...is RF compression all that bad?  It is what most transmit ALC circuits

do.  It would also be possible to make the proposed circuit driven by reflected

power instead of current.  Then we could call it a transmit ALC to protect the

IRF510(s). 

 

It would be fairly simple to add a latching function to the limiter design so that it

totally shuts down output when Imax has been reached.  This is possible but would

then require a RESET button or power cycling to restore power to the RF PA stage.

It is also possible to change the proposed design to put the current sensing ahead

of the control MOSFET and make that MOSFET into a voltage control circuit.  This

was my initial approach but the component count became just too high to be an

internal modification for transceivers.  It would be more suitable for converting

an unregulated power supply to a regulated one. 

 

For those who are using modified PC power supplies it is possible to change the

current sensing so that the switching regulator would shut down if Imax of 2 to 3
amperes is exceeded.  This approach would require power cycling to restore
operation. 

Problem with using fuses is that they have a short but measurable heating period
before they go open.  When they do open they spark internally for another short
period.  Both the delay and the spark are potential problems for circuit components.

Poly-fuse  or resettable fuse devices are intended to address a different issue. 

Some are equivalent of FAST-BLOW fuses, and some are just conventional

resettable circuit breakers.

Suggestion here is that "if you can come up with something else that is adequate,

please submit a circuit drawing and explanation of how it works"  We could all

benefit from that.

Arv  K7HKL
_._

 

On Fri, Jan 26, 2018 at 11:27 AM, Tim Gorman <tgorman2@...> wrote:

A current "limiter" which modulates the current, i.e. limiting the
current no matter the drive level, is like applying an ALC to the
exciter. Improper design can result in compression of the signal which
can then generate spurious responses in the output.

If the current limiter is of a "drop-out" style which requires
resetting then this won't happen, it will just shut down the exciter.
In that case, however, it doesn't provide much efficiency over a plain
old fuse!

tim ab0wr

On Fri, 26 Jan 2018 05:32:08 -0800
"n5ib_2" <n5ib@...> wrote:

> One other possibility to consider to protect against overcurrent
> situations is to use a current limiting power supply, or add a
> current limiter to an existing power supply or battery.
>
> The current limiter circuit whose link is at this site:
> <http://n5ib.net/Index.xht>
> will go up to 2.2 amps, and includes a low-dropout voltage regulator
> that also provides reverse polarity protection.
>
> There is a version, in a different package, of that same regulator
> chip that has an added "tracking" feature - being able to parallel
> multiple chips to increase the available current. Details are on the
> datasheet in the document.
>
> Jim, N5IB
>
>
>



 

Re: New VFO PCB

David Nelson
 

I got mine for the bitx.  Dave  kc2ipx

On Mon, Jan 29, 2018 at 4:12 PM, at91r40008 <yvon@...> wrote:
Dave,

do you use Mike's boards in the Bitx or uBitx?
--
73, Yvon NU6I


Re: FS: Bitx AGC Kits

ramon paulino
 

If already built, how much would it cost me including shipping here in manila Philippines 
Thanks
DU1ZCC
Nomar

On Jan 28, 2018 13:58, "N8DAH" <Dherron@...> wrote:

I have 10 kits ready to go with another 10 for kits or pre-built.

This was posted on DuWayne KV4QB's site found here 

Thank you DuWayne for the use of the board layout and files!

All kits will come with:

PCB x 1

Parts placement layout x 1

2N3904 x 1

2N7000 x 1

47uf x 2

1N4148 x 1

100R x 3

100k x 3

10k x 1 this is extra for the user to play with attack or input values.

2k2 x 1

.1uf x 2 unmarked tan

If you lose anything let me know I will send you a replacement.

This is the 3rd run of the boards, many users here have this AGC already in use myself included. It was setup for the Bitx40 but I have not tested it with the Ubitx yet (should work).

 

Cost and options:

#1 - Kits 13$ shipped

#2 - Pre-built OT service 15$ shipped and tested

Please contact me before you send any money the last two times I have offered just the boards they sold out in under 24 hours.

As before I am not yet a store so please have patience and 1st come 1st serve. If all goes well I have plans to roll the income from this run into purchasing Eagle and making a new adjustable AGC with all surface mount, surface mount led zero beat and more!

Contact me directly for more information or orders: dherron at live dot com

I will send you a confirmation and direct you to my paypal for payment.


--
David

 N8DAH
Kit-Projects.com

Re: Cheap Harbor Freight Case for MBITX

Ken Hansen
 

This 'pelican-style' case is also nice - I'd love to figure out a front panel that snaps over the bottom half of the case (remove all pick-and-pluck)...

On Jan 29, 2018, at 3:47 PM, wishbone_aaa <dlmock@...> wrote:

Just place my order for a MBITX and have been looking for an enclosure. I spotted in my workshop a Harbor Freight plastic ammo box that looks like it will do the job.  With the lid open, the box is 6 inches deep,9 3/4 wide and 4 1/2inches high.  Price $6.99 (even cheaper when there's a coupon).   <https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore%2Cf%2CEAFeatured+Weight%2Cf%2CSale+Rank%2Cf&q=ammo+box>

Re: MAX9814 mic preamp and DC bias capacitor

jlco001@...
 

Partial success. I got the mic to transmit, but audio from the mic comes thru when the the radio on receive. I tried a 10uF polarized capacitor in both directions (uBITX side negative, and then positive) and got the same results. I'm powering the preamp from a battery. I might try getting a double-pole double-throw switch to turn on power only when in transmit. The old HT speaker mic housing I used only has a single-pole switch.

BTW - I set it at 40db and it is HOT!

Thanks for the help!

Jeff