4S-Tuner SWR Red LED


Daniel Walter
 

My tuner seems to work well except for one item. The Red LED does not dim significantly. It does dim a bit and that does correspond to low SWR, but it is very difficult to read. Is there an easy mod to lower the brightness a bit? I suspect I can put a resistor in line or another 1N4148 to dim it, but hoping someone has already played with this and has a solution.
--
72/73, Dan
NM3A


nm0s_qrp
 

Is your green LED ever coming on to full brightness?


Bob Parr
 

I have the same issue and I can get the Green very bright most of the time, but at best red only dims.

Bob
KG5GTE


Adam Allen
 

I have a similar issue. I can get the green LED to full brightness, but at best (even at almost 1:1 SWR according to other gauges) the red only gets dimmer. It doesn’t turn off or even “fully” dim. I’ve learned to live with it but if there’s a fix floating around I’m interested.


Don, W9EBK
 

I'm at work so I don't have time to look at the schematic but from the description it sounds like the current limiting resistance on the Red L.E.D, or the cutoff current of that L.E.D, is too low.  L.E.D.s are usually 20mA, 40mA, or 60mA for maximum brightness,  but the cutoff varies depending on the L.E.D.  If someone wants to do a bit of experimenting, the fix might be as simple as swapping out the Red L.E.D for one of a higher maximum current rating so it cuts off at the signal level of a low SWR.  If there is a resistor in series with that L.E.D then a larger resistor might do the job.

If I get some time tonight I'll take a look at the schematic. 

Don, W9EBK 


On Wed, Mar 3, 2021, 9:29 AM Adam Allen <adamallen@...> wrote:
I have a similar issue.  I can get the green LED to full brightness, but at best (even at almost 1:1 SWR according to other gauges) the red only gets dimmer.  It doesn’t turn off or even “fully” dim. I’ve learned to live with it but if there’s a fix floating around I’m interested. 






W3BNO
 

I had a similar problem with mine. I solved by connecting a 5k trim pot across the red led. With the tuner feeding a 50 ohm dummy load and adjusted for maximum dimming of the red led, I adjusted the pot until the led just extinguished. This does not really effect the sensitivity of the SWR indicator but rather compensates for the required base current into Q1 when Q2 is cut off. I left the pot installed as this is a balance situation so it would be very difficult to match the exact value required using standard value fixed resistors. It would also not be able to accurately calculate the value because it is dependent on the small signal current gain of Q1 and the threshold current of the LED. This worked for me hope it helps.   W3BNO


On Mar 3, 2021, at 9:49 AM, Don, W9EBK <donw9ebk@...> wrote:

I'm at work so I don't have time to look at the schematic but from the description it sounds like the current limiting resistance on the Red L.E.D, or the cutoff current of that L.E.D, is too low.  L.E.D.s are usually 20mA, 40mA, or 60mA for maximum brightness,  but the cutoff varies depending on the L.E.D.  If someone wants to do a bit of experimenting, the fix might be as simple as swapping out the Red L.E.D for one of a higher maximum current rating so it cuts off at the signal level of a low SWR.  If there is a resistor in series with that L.E.D then a larger resistor might do the job.

If I get some time tonight I'll take a look at the schematic. 

Don, W9EBK 

On Wed, Mar 3, 2021, 9:29 AM Adam Allen <adamallen@...> wrote:
I have a similar issue.  I can get the green LED to full brightness, but at best (even at almost 1:1 SWR according to other gauges) the red only gets dimmer.  It doesn’t turn off or even “fully” dim. I’ve learned to live with it but if there’s a fix floating around I’m interested. 






Daniel Walter
 

NM0S:  Yes, green LED does go to full brightness. 


WB3BNO:  That's kind of what I thought might be a good option. I will have to try that. 
--
72/73, Dan
NM3A


Daniel Walter
 

Did some more testing. 5W input.

With 50 ohm dummy load, can get red LED to almost go out which corresponds to almost no reflected power confirmed with independent meter.

Detuning slightly shows red LED is at full brightness at about 1.3 SWR (with resistive bridge in 4S Tuner switched in). This corresponds to about 2.0 SWR into antenna alone. So I guess I simply was only able to tune to slightly below 2:1 SWR with certain antennas. Looks like it was really operator interpretation error!

Thanks for the responses from all.

Dan
Sent from NM3A




--
72/73, Dan
NM3A


David Wilcox K8WPE
 

This makes great sense to me.  There are many micro pots available so look for one small enough to fit inside the case. Great idea.

David J. Wilcox’s iPad

On Mar 3, 2021, at 1:00 PM, W3BNO <Jfitzer1053@...> wrote:


I had a similar problem with mine. I solved by connecting a 5k trim pot across the red led. With the tuner feeding a 50 ohm dummy load and adjusted for maximum dimming of the red led, I adjusted the pot until the led just extinguished. This does not really effect the sensitivity of the SWR indicator but rather compensates for the required base current into Q1 when Q2 is cut off. I left the pot installed as this is a balance situation so it would be very difficult to match the exact value required using standard value fixed resistors. It would also not be able to accurately calculate the value because it is dependent on the small signal current gain of Q1 and the threshold current of the LED. This worked for me hope it helps.   W3BNO


On Mar 3, 2021, at 9:49 AM, Don, W9EBK <donw9ebk@...> wrote:

I'm at work so I don't have time to look at the schematic but from the description it sounds like the current limiting resistance on the Red L.E.D, or the cutoff current of that L.E.D, is too low.  L.E.D.s are usually 20mA, 40mA, or 60mA for maximum brightness,  but the cutoff varies depending on the L.E.D.  If someone wants to do a bit of experimenting, the fix might be as simple as swapping out the Red L.E.D for one of a higher maximum current rating so it cuts off at the signal level of a low SWR.  If there is a resistor in series with that L.E.D then a larger resistor might do the job.

If I get some time tonight I'll take a look at the schematic. 

Don, W9EBK 

On Wed, Mar 3, 2021, 9:29 AM Adam Allen <adamallen@...> wrote:
I have a similar issue.  I can get the green LED to full brightness, but at best (even at almost 1:1 SWR according to other gauges) the red only gets dimmer.  It doesn’t turn off or even “fully” dim. I’ve learned to live with it but if there’s a fix floating around I’m interested. 






Curt M.
 

I’ve noticed with mine that you can sometimes get a deeper null in tuning with a different letter setting on the dial. Be sure to try tuning the same band/antenna using a letter close to what you are currently using. Also try different combinations of your left and right knobs to get the best null.  

I keep a list of the best settings for antenna/band in the notes section of my iPhone for quick reference. 

Curt
WU3U