?

How likely is this to happen? Bitx40 connected to 40M resonant antenna perpendicular to another antenna with a 100W transceiver running a Winlink gateway.

I fully expect front-end overload and nasty noises, but will the coupling cause actual damage> I would like to leave the bitx40 running but volume minimized to lessen drift during warm-up period.

Currently I leave it running but antenna dis-connected, but it is only a matter to time until my feeble brain forgets.

Thomas W Noel
KF7RSF

On Dec 16, 2016, at 9:07 PM, Raj vu2zap@... [BITX20] <BITX20@...> wrote:

Thomas,

At pin 12 of K1 relay solder 2 4148 diodes in parallel but in opposite polarity. This will limit the receiver from getting high RF voltage.?

Also if you cut the track between K1 pin 12 and K2 pin 14 and insert a 12v 60 or 40 ma miniature incandescent bulb it would be better. This is common protection method in commercial transceivers and amps. This track seems to be on the component side.

?

cheaper still!

?

73 Raj vu2zap

At 17/12/2016, you wrote:

??

How likely is this to happen? Bitx40 connected to 40M resonant antenna perpendicular to another antenna with a 100W transceiver running a Winlink gateway.

I fully expect front-end overload and nasty noises, but will the coupling cause actual damage> I would like to leave the bitx40 running but volume minimized to lessen drift during warm-up period.

Currently I leave it running but antenna dis-connected, but it is only a matter to time until my feeble brain forgets.

Thomas W Noel
KF7RSF

?

Raj,

Thank you for the response. You confirm my fear that the danger of damage is real and present.

I am very much a beginner at this sort of work. I have excellent mechanical and soldering skills, but know little of circuit elements beyond what was required for my license.

I believe you have offered two possible ways to mitigate the risk - either the diodes OR the incandescent bulb. Correct?

If I choose the diodes in parallel, I assume one lead of each goes to pin 12 of K1 relay. Does the other lead of each go to ground? Or where? Be gentle please!

If I choose the miniature bulb, does that bulb function as a sacrificial element like a gas discharge arrestor cartridge? Or is it able to absorb and limit the voltage? I can do either, and it seems you are saying the second option is better.

I?€?m learning as fast as I can!

Thomas W Noel
KF7RSF

On Dec 16, 2016, at 9:07 PM, Raj vu2zap@... [BITX20] <BITX20@... > wrote:

Thomas,

At pin 12 of K1 relay solder 2 4148 diodes in parallel but in opposite polarity. This will limit the receiver from getting high RF voltage.

Also if you cut the track between K1 pin 12 and K2 pin 14 and insert a 12v 60 or 40 ma miniature incandescent bulb it would be better. This is common protection method in commercial transceivers and amps. This track seems to be on the component side.



cheaper still!



73 Raj vu2zap

At 17/12/2016, you wrote:

?

How likely is this to happen? Bitx40 connected to 40M resonant antenna perpendicular to another antenna with a 100W transceiver running a Winlink gateway.

I fully expect front-end overload and nasty noises, but will the coupling cause actual damage> I would like to leave the bitx40 running but volume minimized to lessen drift during warm-up period.

Currently I leave it running but antenna dis-connected, but it is only a matter to time until my feeble brain forgets.

Thomas W Noel
KF7RSF

On Dec 17, 2016, at 3:41 AM, Raj vu2zap@... [BITX20] <BITX20@...> wrote:

Thomas,

I would recommend you do both. The diodes may not take the all power from your other antenna.

Yes the two diodes in parallel are connected between pin 12 of k1 and ground. Both diodes should be
connected in opposite polarity. The line marking the cathode of one should go to ground and
the other diode's cathode should got to pin 12 (Rx antenna line). This will limit the voltage to
less than one volt and that wont damage the Rx.

The bulb is useful for preventing the diodes from blowing up by dissipating excess incoming power.

I used to run a 10M packet bbs link and another antenna was for my base HF. When one transmitted
the other rig lamp used to glow.

You can check the power received by connecting a QRP power meter on the 40M antenna and?
the other port of the meter to a dummy load. You will find out? how much power is picked up by the?
40M antenna when you transmit on the main winlink antenna.

I forget a lot too @ 60! The doctor asked to visit again when I start to forget my XYLs name!

Cheers
Raj
vu2zap


At 17/12/2016, you wrote:

??

Raj,

Thank you for the response. You confirm my fear that the danger of damage is real and present.

I am very much a beginner at this sort of work. I have excellent mechanical and soldering skills, but know little of circuit elements beyond what was required for my license.

I believe you have offered two possible ways to mitigate the risk - either the diodes OR the incandescent bulb. Correct?

If I choose the diodes in parallel, I assume one lead of each goes to pin 12 of K1 relay. Does the other lead of each go to ground? Or where? Be gentle please!

If I choose the miniature bulb, does that bulb function as a sacrificial element like a gas discharge arrestor cartridge? Or is it able to absorb and limit the voltage? I can do either, and it seems you are saying the second option is better.

I???m learning as fast as I can!

Thomas W Noel
KF7RSF

On Dec 16, 2016, at 9:07 PM, Raj?vu2zap@...?[BITX20] <BITX20@...?> wrote:

Thomas,

At pin 12 of K1 relay solder 2 4148 diodes in parallel but in opposite polarity. This will limit the receiver from getting high RF voltage.?

Also if you cut the track between K1 pin 12 and K2 pin 14 and insert a 12v 60 or 40 ma miniature incandescent bulb it would be better. This is common protection method in commercial transceivers and amps. This track seems to be on the component side.



cheaper still!



73 Raj vu2zap

At 17/12/2016, you wrote:

??

How likely is this to happen? Bitx40 connected to 40M resonant antenna perpendicular to another antenna with a 100W transceiver running a Winlink gateway.

I fully expect front-end overload and nasty noises, but will the coupling cause actual damage> I would like to leave the bitx40 running but volume minimized to lessen drift during warm-up period.

Currently I leave it running but antenna dis-connected, but it is only a matter to time until my feeble brain forgets.

Thomas W Noel
KF7RSF

?

Raj's suggestion of two back-to-back 2n4148 diodes between K1 pin 12 and ground?puts them only in the receive signal path. ?That seems the ideal spot.?

K1 pin 14 is in the transmit signal path, a?relatively low level signal from the exciter into Q13.

Perhaps you were looking at K2 when you suggested pin 14?

K2 pin 14 is only in the receive path, but does not have the benefit of the impedance of that long trace from K2 to K1, which might keep the diodes from blowing.

Jerry, KE7ER

---In BITX20@..., wrote :

?Looking at the schematic, I would put the diodes between pin 14 and ground.
?This puts them in RX? only. ?

On Dec 28, 2016, at 1:11 AM, jgaffke@... [BITX20] <BITX20@...> wrote:

?

Raj's suggestion of two back-to-back 2n4148 diodes between K1 pin 12 and ground?puts them only in the receive signal path. ?That seems the ideal spot.?

K1 pin 14 is in the transmit signal path, a?relatively low level signal from the exciter into Q13.

Perhaps you were looking at K2 when you suggested pin 14?

K2 pin 14 is only in the receive path, but does not have the benefit of the impedance of that long trace from K2 to K1, which might keep the diodes from blowing.

Jerry, KE7ER

---In BITX20@..., <wa2yne@...> wrote :

?Looking at the schematic, I would put the diodes between pin 14 and ground.
?This puts them in RX? only. ?

?

Yup, 1n4148's, or whatever it was that Raj was suggesting.

Would be very tough to find some 2n4148 diodes ;-)

?

---In BITX20@..., wrote :

Jerry - don't you mean 1n4148 diodes , not 2n4148? Please advise. 73 w4usf

Sent from my iPad

On Dec 28, 2016, at 1:11 AM, jgaffke@... [BITX20] <BITX20@...> wrote:

?

Raj's suggestion of two back-to-back 2n4148 diodes between K1 pin 12 and ground?puts them only in the receive signal path. ?That seems the ideal spot.?

K1 pin 14 is in the transmit signal path, a?relatively low level signal from the exciter into Q13.

Perhaps you were looking at K2 when you suggested pin 14?

K2 pin 14 is only in the receive path, but does not have the benefit of the impedance of that long trace from K2 to K1, which might keep the diodes from blowing.

Jerry, KE7ER

---In BITX20@..., wrote :

?Looking at the schematic, I would put the diodes between pin 14 and ground.
?This puts them in RX? only. ?

?

No doubt, Jerry, I was just afraid that someone with less knowledge ( like me :) ) might order the 2n4148s without understanding the difference. 73 and thanks for advising.

Sent from my iPad

On Dec 28, 2016, at 3:10 PM, jgaffke@... [BITX20] <BITX20@... > wrote:

?


Yup, 1n4148's, or whatever it was that Raj was suggesting.
Would be very tough to find some 2n4148 diodes ;-)
?

---In BITX20@..., wrote :

Jerry - don't you mean 1n4148 diodes , not 2n4148? Please advise. 73 w4usf

Sent from my iPad

On Dec 28, 2016, at 1:11 AM, jgaffke@... [BITX20] <BITX20@... > wrote:

?


Raj's suggestion of two back-to-back 2n4148 diodes between K1 pin 12 and ground puts them only in the receive signal path.? That seems the ideal spot.

K1 pin 14 is in the transmit signal path, a relatively low level signal from the exciter into Q13.
Perhaps you were looking at K2 when you suggested pin 14?
K2 pin 14 is only in the receive path, but does not have the benefit of the impedance of that long trace from K2 to K1, which might keep the diodes from blowing.

Jerry, KE7ER


---In BITX20@..., wrote :
?Looking at the schematic, I would put the diodes between pin 14 and ground.
?This puts them in RX? only.?

I understand that the specifics are for the Bitx40, however some of the comments were that it was used on commercial rigs to protect receiver front ends.? Would be interested in the reason it would not apply to other rigs inputs, as long as it was only in the receiver path from the antenna to the first mixer.? There is Q90 in the uBitx that is possibly vulnerable to the overload problem as in the? Bitx40 Q13(?).

Thank-you for the response