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Minimum Hack

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What are the minimum hardware and software hacks that a new user should plan to make upon receipt of the standard product?

There are a lot of great ideas out there. What say you?

James
 

Should probably add the two 1N4148 diodes from relay K1 pin 12 to ground to prevent damage to Q13 from a nearby TX. Also should add the 100 pf capacitor across L7 in the output filter to reduce the second harmonic.

AL
 

James

I would recommend first getting it together and make sure it is working the way that it should.

Hacks, depends on what you want to do.

Look at the tips and mods document in here -



Pete Juliano N6QW has several -?


Has lots of resources to check out.

Randy, K7AGE
BITX40 SN 02-139
 

There are really two required minimum hacks for the BITX40.

1) You must stabilize the VFO. It drifts too much for comfort. The
best fixes mean replacing the VFO caps with CoG or NPO units
and stabilizing L4. Others have replaced it with a DDS.

2) You must make sure the transmitter is legal for use in the US.
It used to be that there was a lot more lax interpretation of
spurious signals for a QRP rig. But the later Part 97 rules,
which govern amateur radio, impose uniform regulations
on all transmitters. That means primarily suppressing the
2nd harmonic of your signal. There are at least 2 fixes for
this in the mods lists.

You do have a copy of the Part 97 rules, don't you? If
not. GET ONE. Every amateur must be familiar with it.

All the other mods are "improvements" or "enhancements".
Nice to have, but not vital to proper operation.

john
AD5YE
 

Sounds like you are getting a new Bitx40 with the Raduino, that VFO will be plenty stable.

The other issue that John mentions can be dealt with by adding a 100pf cap across L7 to suppress the second harmonic: ? ??/g/BITX20/message/22366



On Thu, Feb 23, 2017 at 08:58 pm, John Backo wrote:

There are really two required minimum hacks for the BITX40.

?
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Al,

Finishing my new unit and saw this thread. ? ?I did not see the two diodes (to protect Q13) in the mods or hacks sections. ?Could you explain further how the two diodes are connected and where? ?Are these from pin 1 to ground (my K1 only has 8 pins not 12)??


Thanks,

Gene

N2IJF
[email protected]
 

Never mind, I found another message which explained the diode arrangement and reviewing the schematic and datasheet for K1 realized that there are only 8 pins but the pin count is based on a 16 pin DIP.


OK now.

Thanks.
 

Hi Al

Could you possibly put this on the Bitx Hacks?

73

Ken VA3ABN

On Wed, Mar 1, 2017 at 11:43 PM, Al Duncan VE3RRD <ve3rrd@...> wrote:

Here is a picture of the location for the two 1N4148 diodes.
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Did my best to ohm out the traces and checked web based data.

Pinout of K1 is the same as a 16 pin dip with the same spacing so some pin counts must be skipped.

Pinout for bottom view of K1 (Easy to find pin 16 as it is grounded):

16 1
blank blank
14 ? ? ? ? 3
blank blank
12 ? ? ? ? 5
blank blank
blank blank
9 ? ? ? ? 8

The attached photo shows the diodes attached from Pin 12 to Pin 16 (TX to Gnd) and two wires for TX LED (pin 1 to Gnd).

So my question is should the diodes be from pin 12 or pin?14 of K1 (or does it matter as the two are connected in the unenergized condition)?

Gene?
N2IJF

K1.JPG

Gene Nitschke
 

?OOPs meant to say?

"The attached photo shows the diodes attached from Pin 12 to Pin 16 (K2-14 to Gnd) and two wires for TX LED (pin 1 to Gnd)."

Pinout also got reformatted hope below version is better.

16????????????1
blank????????blank
14????????????3
blank????????blank
12????????????5
blank????????blank
blank????????blank
9????????????????8


Gene
 

"So my question is should the diodes be from pin 12 or pin 14 of K1 (or does it matter as the two are connected in the unenergized condition)?"

It doesn't matter. You are protecting the RX input
from the antenna against a very strong signal.
As long as it is on that line, the function is good.

That being said, it is probably a bit smarter to put the
diodes on the receiver input side rather than the antenna side,
since it is that which you are protecting, and that way you
can account for any relay contact lag or other strong signal.

john
AD5YE
 

The diodes are to protect Q13's base from strong signals during receive only, the diodes shouldn't be connected to Q13 in transmit (Q13 is a transmitter pre-driver). Using the K1 pin numbers shown on the schematic at , they should be between K1 pin 12 and ground - that way they will only be connected during receive and also provide protection to the RX circuitry. On the top of the BITX40v3 board, you can see the trace coming from C132 (which goes to Q13 base) and connecting to K1 pin 12. If the diodes are connected to K1 pin 14, they will always be in the circuit, even during TX. Without these diodes, a number of people have had Q13 fail when a strong (100W) TX is on an antenna located near the BITX40v3 antenna.
 

Al is absolutely right. You can't put a diode in the transmit circuit.
It has to be on the antenna side so that it doesn't conduct during TX.
As noted, this is to protect a rather sensitive Q13 from overload during RX
since it is in a common circuit for RX and TX.

Mea culpa.

john
AD5YE
 

Just to be obnoxious: ?Mostly right, though not absolutely right. ?Voltages at K1-14 are around 200mv rms max of 7mhz during transmit, 1n4148's there would not conduct more than a few microamps till voltages got beyond double that. ?But I'll agree with John that ?K1-12 to ground is the logical place, that's where I put them.?


On Sun, Mar 5, 2017 at 09:01 pm, John Backo wrote:

Al is absolutely right. You can't put a diode in the transmit circuit.

?
 

Note that the previous picture mistakenly shows the diodes connected between K1 pin 14 and ground. They should be between pin 12 and ground:?

 

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Thank you Al.

?

I will be applying and testing this fix tonight.

?

John Beasley

KG7UMN

?

?

From: [email protected] [mailto:[email protected]] On Behalf Of Al Duncan VE3RRD
Sent: Friday, April 14, 2017 8:06 AM
To: [email protected]
Subject: Re: [BITX20] Minimum Hack

?

Note that the previous picture mistakenly shows the diodes connected between K1 pin 14 and ground. They should be between pin 12 and ground:?

Ralph Mills
 

Here is the two hacks discussed in this thread the left is the 100pf across L7, the right is the two 1n4148 diodes placed across K1 pins 12 and 14(gnd).?
Ralph Mills
 


Here is the two hacks discussed in this thread the left is the 100pf across L7, the right is the two 1n4148 diodes placed across K1 pins 12 and 16(gnd)

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