Topics

Q90 #v3


Bill Cromwell
 

A handful of 2N3904 transistors arrived today. My V3 should be back on the air soon! What should be handful of parts is more like a teaspoonful.

See you on the air.

73,

Bill KU8H

--
bark less - wag more


Slurm
 

Hi Bill KU8H

Q90 seems to appear a lot in discussions.  What destroys Q90 ? 

Thanks in advance

Slurm


Bill Cromwell
 

Hi,

Too much voltage coming into the antenna line. A nearby transmitter or lightning induced surge or even just wind static.

73,

Bill KU8H

bark less - wag more

On 10/14/20 10:35 AM, Slurm wrote:
Hi Bill KU8H
Q90 seems to appear a lot in discussions.  What destroys Q90 ?
Thanks in advance
Slurm


 

Make sure to do this at the same time you replace Q90:

Back to Back Diodes to Protect Q90

The picture is appropriate for v3 and v4 boards.  I'm not sure for v5 or v6 because the relay scheme is different.  Someone with one of those versions could confirm it please?

73,   Mark


Kit Peters
 

What diodes do you use there?

On Wed, Oct 14, 2020 at 10:12 AM Mark - N7EKU <n7eku@...> wrote:
Make sure to do this at the same time you replace Q90:

Back to Back Diodes to Protect Q90

The picture is appropriate for v3 and v4 boards.  I'm not sure for v5 or v6 because the relay scheme is different.  Someone with one of those versions could confirm it please?

73,   Mark



--
Kit Peters, W0KEH
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Evan Hand
 

Kit,

The diodes that I used were 1n4148.  Any small signal diode similar to the old 1n914 should work.  You want fairly fast diodes.

The v5 boards have the same layout for K1 as the others.  I am sure that is also the case for the v6.  I have both v4 and v5, I do not have a v6.  I did look at the schematics and they are the same in that section, as well as the general layout from pictures.  You can get the schematics from HFSignals.

73
Evan
AC9TU


iz oos
 

In some RX receiver protectors I use back to back schottky diodes and an Small lamp in series. Maybe they could be allocated somewhere within the ubitx. For statics I believe you might add a 1Mohm resistore in parallel at the antenna connector or a large inductors.


Il mer 14 ott 2020 05:28 PM Evan Hand <elhandjr@...> ha scritto:
Kit,

The diodes that I used were 1n4148.  Any small signal diode similar to the old 1n914 should work.  You want fairly fast diodes.

The v5 boards have the same layout for K1 as the others.  I am sure that is also the case for the v6.  I have both v4 and v5, I do not have a v6.  I did look at the schematics and they are the same in that section, as well as the general layout from pictures.  You can get the schematics from HFSignals.

73
Evan
AC9TU


Gordon Gibby
 

There’s a series capacitor that gets charged up & the reverse voltage destroys the base enitter Junction.  That’s my theory anyway and I’m sticking to it! Explained it several times before on these pages.  


On Oct 14, 2020, at 11:43, iz oos <and2oosiz2@...> wrote:


In some RX receiver protectors I use back to back schottky diodes and an Small lamp in series. Maybe they could be allocated somewhere within the ubitx. For statics I believe you might add a 1Mohm resistore in parallel at the antenna connector or a large inductors.

Il mer 14 ott 2020 05:28 PM Evan Hand <elhandjr@...> ha scritto:
Kit,

The diodes that I used were 1n4148.  Any small signal diode similar to the old 1n914 should work.  You want fairly fast diodes.

The v5 boards have the same layout for K1 as the others.  I am sure that is also the case for the v6.  I have both v4 and v5, I do not have a v6.  I did look at the schematics and they are the same in that section, as well as the general layout from pictures.  You can get the schematics from HFSignals.

73
Evan
AC9TU


 

Thank you Kit for confirming that,

So this protection circuit will work on all versions.  Just follow the picture and use small signal diodes (1n4148, 1n914, etc).

Iz, the receive line is grounded already at T2.  The problem with static is the voltage build-up that can occur when the antenna is not connected.  Then upon connection, the rig receives a large jolt of voltage.  For static protection, you want something that will continuously drain the charge.  This can be done with the large value resistor (1 Mohm) connected between the two antenna leads.  It is handy to do this on the lead in to the shack, or on an antenna switch.

Or if you remember everytime, you can just temporarily short the coax connector before you hook it up.

73,   Mark


 

Ooops, I meant Evan!


Kit Peters
 

I'm planning to build a combination static drain / lightning protection circuit similar to what M0LMK has: https://www.m0lmk.co.uk/2018/04/30/ladder-line-surge-suppressor/

73, Kit


On Wed, Oct 14, 2020 at 11:11 AM Mark - N7EKU <n7eku@...> wrote:
Thank you Kit for confirming that,

So this protection circuit will work on all versions.  Just follow the picture and use small signal diodes (1n4148, 1n914, etc).

Iz, the receive line is grounded already at T2.  The problem with static is the voltage build-up that can occur when the antenna is not connected.  Then upon connection, the rig receives a large jolt of voltage.  For static protection, you want something that will continuously drain the charge.  This can be done with the large value resistor (1 Mohm) connected between the two antenna leads.  It is handy to do this on the lead in to the shack, or on an antenna switch.

Or if you remember everytime, you can just temporarily short the coax connector before you hook it up.

73,   Mark



--
Kit Peters, W0KEH
GPG public key fingerpint: D4FF AA62 AFEA 83D6 CC98 ACE5 6FAE 7E74 7F56 ED1D
Hello to any and all NSA, DEA, or other government or non-government agents reading this email.  Tell me about your life; I'll tell you about mine.


Evan Hand
 

Gordon,
I like your explanation.

All,
Here is a reference that I found on protecting receiver front ends:
http://www.na0tc.org/lib/exe/fetch.php?media=technical:rx_protect.pdf

I had planned to use the lamp in series between K3 and K1 in the receive section.  I even bought the recommended lamps.  The lamp has low losses on receive and is switched out on transmit.  You also need the back to back diodes to limit the voltage level.  Not sure if the capacitors are needed.

I have installed just the diodes thus far and have not had an issue yet.  I also have a spare 2n3904 in case I do toast a Q90.

73
Evan
AC9TU


Slurm
 

Great to have all the responses on this issue.  A great thread to keep and should be a suggested mod if it isn't already.

Thanks to all for responding !

73's

Slurm


 

I used the single channel version of these on another project and thought they might be good for the uBITx. https://www.onsemi.com/pub/Collateral/CM1213A-D.PDF They are small but pretty easy to solder to.

Joel
N6ALT