Relay for antenna tuner output?


Rob French (KC4UPR)
 

I use one of those N1DDC-style automatic antenna tuners from Russia (eBay) with my uBITX.  I've been thinking about building a dummy load into the antenna tuner case (or even external for that matter, with a BNC), and making it so that:

(a) I can select between the dummy load or the antenna via a pushbutton, and

(b) Anytime the tuner is turned off, it will automatically switch to the dummy load, as a modest safety measure.

Does anyone have a recommendation as to the type of SPDT relay that I should use for this?  What parameters do I need to consider? Obviously voltage level (accounting for both max power output, and high SWR conditions), but is there anything else?  Anything for maintaining impedance?  (I'm guessing not really, at HF.  But I don't know.)

Thanks!
-Rob KC4UPR


Clark Martin
 

Use the some model of relay as in the antenna tuner. If it isn’t adequate, the tuner is in trouble.



Clark Martin
KK6ISP

On Aug 22, 2020, at 9:06 PM, Rob French (KC4UPR) <kc4upr@...> wrote:

I use one of those N1DDC-style automatic antenna tuners from Russia (eBay) with my uBITX. I've been thinking about building a dummy load into the antenna tuner case (or even external for that matter, with a BNC), and making it so that:

(a) I can select between the dummy load or the antenna via a pushbutton, and

(b) Anytime the tuner is turned off, it will automatically switch to the dummy load, as a modest safety measure.

Does anyone have a recommendation as to the type of SPDT relay that I should use for this? What parameters do I need to consider? Obviously voltage level (accounting for both max power output, and high SWR conditions), but is there anything else? Anything for maintaining impedance? (I'm guessing not really, at HF. But I don't know.)


Bob, N1KPR
 

I'm using a chassis mounted dummy load which is selected via a toggle switch. This is handy for adjusting the SWR and Power meters. Then when I switch to the antenna I can see the real SWR and power output to the antenna line.
You can see it on my video at around the 3:30 minute mark.
Bob, N1KPR





Arv Evans
 

Bob  N1KPR

Using a switch to connect to either dummy load or antenna is a good idea.  It should help eliminate errors where the rig is not connected to anything.  

Arv  K7HKL
_._


On Sun, Aug 23, 2020 at 6:42 AM Bob, N1KPR <rwbetts@...> wrote:
I'm using a chassis mounted dummy load which is selected via a toggle switch. This is handy for adjusting the SWR and Power meters. Then when I switch to the antenna I can see the real SWR and power output to the antenna line.
You can see it on my video at around the 3:30 minute mark.
Bob, N1KPR





Rob French (KC4UPR)
 

Clark,

Thanks!  I'm going to file that under, "Duh... why didn't I think of that..."  I suspect I won't be able to source the exact part, but I see the parameters printed on the tops of the relays, so I'll examine them and find something comparable from Mouser.

Bob/Arv,

Yep, that's essentially what I'm looking to do.  Just would be using a relay so that I can automate the process when I turn off the tuner.  My goals with this arrangement are:

(1) If I disconnect the antenna for lightning safety, and forget to plug it back in, I can have it default to "dummy load" when it starts up, so that there is always something good connected to the rig.

(2) If I forget to disconnect the antenna for lightning safety, at least there is some alternate path to ground for any discharges, that don't go through my rig.  (I realize this won't save me from a direct hit, but perhaps from whatever recent discharge killed the TX on another of my rigs... no lightning strike to the house that I'm aware of, but killed a diode in my tuner, killed the TX output of the other rig, and killed the rig's external power supply...)   I think I would need a DPDT relay in this case, or maybe two relays, to (a) automatically switch the rig to the dummy load, and (b) switch the antenna to ground.

Thanks again for the input!

-Rob KC4UPR


Arv Evans
 

Rob KC4UPR

Back in the bad old days some of us used to hang a 2W non-inductive resistor across the antenna or coax connections.  This bleeds of precipitation or wind caused static and hopefully saved equipment from close-by lightning strikes.  
We also used gas tube voltage limiters for additional protection.  Probably 
nothing would save equipment from a direct strike.

Arv  K7HKL
_._


On Sun, Aug 23, 2020 at 11:30 AM Rob French (KC4UPR) <kc4upr@...> wrote:
Clark,

Thanks!  I'm going to file that under, "Duh... why didn't I think of that..."  I suspect I won't be able to source the exact part, but I see the parameters printed on the tops of the relays, so I'll examine them and find something comparable from Mouser.

Bob/Arv,

Yep, that's essentially what I'm looking to do.  Just would be using a relay so that I can automate the process when I turn off the tuner.  My goals with this arrangement are:

(1) If I disconnect the antenna for lightning safety, and forget to plug it back in, I can have it default to "dummy load" when it starts up, so that there is always something good connected to the rig.

(2) If I forget to disconnect the antenna for lightning safety, at least there is some alternate path to ground for any discharges, that don't go through my rig.  (I realize this won't save me from a direct hit, but perhaps from whatever recent discharge killed the TX on another of my rigs... no lightning strike to the house that I'm aware of, but killed a diode in my tuner, killed the TX output of the other rig, and killed the rig's external power supply...)   I think I would need a DPDT relay in this case, or maybe two relays, to (a) automatically switch the rig to the dummy load, and (b) switch the antenna to ground.

Thanks again for the input!

-Rob KC4UPR


robert pohorence
 

1 to 2 megohms , at least 1/4 wat is OK 
Rob 

On Sun, Aug 23, 2020 at 3:45 PM Arv Evans <arvid.evans@...> wrote:
Rob KC4UPR

Back in the bad old days some of us used to hang a 2W non-inductive resistor across the antenna or coax connections.  This bleeds of precipitation or wind caused static and hopefully saved equipment from close-by lightning strikes.  
We also used gas tube voltage limiters for additional protection.  Probably 
nothing would save equipment from a direct strike.

Arv  K7HKL
_._


On Sun, Aug 23, 2020 at 11:30 AM Rob French (KC4UPR) <kc4upr@...> wrote:
Clark,

Thanks!  I'm going to file that under, "Duh... why didn't I think of that..."  I suspect I won't be able to source the exact part, but I see the parameters printed on the tops of the relays, so I'll examine them and find something comparable from Mouser.

Bob/Arv,

Yep, that's essentially what I'm looking to do.  Just would be using a relay so that I can automate the process when I turn off the tuner.  My goals with this arrangement are:

(1) If I disconnect the antenna for lightning safety, and forget to plug it back in, I can have it default to "dummy load" when it starts up, so that there is always something good connected to the rig.

(2) If I forget to disconnect the antenna for lightning safety, at least there is some alternate path to ground for any discharges, that don't go through my rig.  (I realize this won't save me from a direct hit, but perhaps from whatever recent discharge killed the TX on another of my rigs... no lightning strike to the house that I'm aware of, but killed a diode in my tuner, killed the TX output of the other rig, and killed the rig's external power supply...)   I think I would need a DPDT relay in this case, or maybe two relays, to (a) automatically switch the rig to the dummy load, and (b) switch the antenna to ground.

Thanks again for the input!

-Rob KC4UPR


--
Rob N8RT


Arv Evans
 

Don't know what others used.  I had a handful of 470K 2W NI that came from a surplus dealer.
_._

On Sun, Aug 23, 2020 at 2:09 PM robert pohorence <mcyman@...> wrote:
1 to 2 megohms , at least 1/4 wat is OK 
Rob 

On Sun, Aug 23, 2020 at 3:45 PM Arv Evans <arvid.evans@...> wrote:
Rob KC4UPR

Back in the bad old days some of us used to hang a 2W non-inductive resistor across the antenna or coax connections.  This bleeds of precipitation or wind caused static and hopefully saved equipment from close-by lightning strikes.  
We also used gas tube voltage limiters for additional protection.  Probably 
nothing would save equipment from a direct strike.

Arv  K7HKL
_._


On Sun, Aug 23, 2020 at 11:30 AM Rob French (KC4UPR) <kc4upr@...> wrote:
Clark,

Thanks!  I'm going to file that under, "Duh... why didn't I think of that..."  I suspect I won't be able to source the exact part, but I see the parameters printed on the tops of the relays, so I'll examine them and find something comparable from Mouser.

Bob/Arv,

Yep, that's essentially what I'm looking to do.  Just would be using a relay so that I can automate the process when I turn off the tuner.  My goals with this arrangement are:

(1) If I disconnect the antenna for lightning safety, and forget to plug it back in, I can have it default to "dummy load" when it starts up, so that there is always something good connected to the rig.

(2) If I forget to disconnect the antenna for lightning safety, at least there is some alternate path to ground for any discharges, that don't go through my rig.  (I realize this won't save me from a direct hit, but perhaps from whatever recent discharge killed the TX on another of my rigs... no lightning strike to the house that I'm aware of, but killed a diode in my tuner, killed the TX output of the other rig, and killed the rig's external power supply...)   I think I would need a DPDT relay in this case, or maybe two relays, to (a) automatically switch the rig to the dummy load, and (b) switch the antenna to ground.

Thanks again for the input!

-Rob KC4UPR


--
Rob N8RT


Bob Lunsford
 

For the V6, etc., an easy dummy load is to mount four 200 Ohm, 2W resistors in parallel on end with leads long enough to keep any heat isolated from other components and to give a bit more heat radiating ability.

This is the "dummy load" used for the Heath QRP rigs. I still use it as a quick/instantaneous test dummy load for my 100W rig. By instantaneous I mean just long enough to see the power out needle jump up. Checking with a finger reveals it only gets slightly warm.

When I want to give my radio a bit more isolation from the antenna, I always switch to the dummy load. Not as good as shorting the antenna out but good for my peace of mind, anyway.

Bob — KK5R

On Sunday, August 23, 2020, 8:42:43 AM EDT, Bob, N1KPR <rwbetts@...> wrote:


I'm using a chassis mounted dummy load which is selected via a toggle switch. This is handy for adjusting the SWR and Power meters. Then when I switch to the antenna I can see the real SWR and power output to the antenna line.
You can see it on my video at around the 3:30 minute mark.
Bob, N1KPR





Bob Lunsford
 

Speaking of the power of lightening, I had a repeater up in central Texas for about three years. I had a 1/4 wave vertical at 50-ft for the receiver and a 1/4 wave vertical at 30-ft on the same tower mounted upside-down and used root beer can cavities (four of them) and the repeater worked fine. Made with VHF Engineering kit boards. Was a local repeater designed for about a 15-20 mile radius in the Killeen-Fort Hood area.

Once when a warning about a tremendous thunder storm was almost on top of us, I disconnected the antennas. I left the BNC connector hanging about six inches away from the repeater and when across the room at the time of the storm, I kept hearing some snapping sounds and looked at the transmitter antenna (about halfway up the tower) and saw sparking about every second or so. This meant that there was at least a voltage of about 2800 volts on the antenna, across the ground. From then on, when I disconnected the antenna, I also plugged it into a shorted connector to "bleed off" the charge.

To save our radios, this should be kept in mind if we need to disconnect for a storm. The antennas connectors also need to be shorted out. Some antenna switches do this by design and, for me, are worth the extra dollars to get one. If, on the other hand, lightening does strike, there is enough energy involved that nothing short of grounding everything will keep damage to a minimum.

I saw a TV antenna had been hit by lightening and the stroke came down the twinlead and entered the floor seeking the concrete base underneath. Tore up the carpet for about ten feet. Surprised to find that the TV was still working. The lightening had bypassed the TV and jumped from the twinlead straight to the floor. The bend in the twinlead saved the TV.

I live in a stormy area and hams in the KY, OH, WV and TN areas pull the plug when storms come in. Too many of them regret not doing so in the past. We must consider our uBITX radios and their antennas equally prone to damage in case of a lightening strike.

Bob — KK5R

On Sunday, August 23, 2020, 3:45:27 PM EDT, Arv Evans <arvid.evans@...> wrote:


Rob KC4UPR

Back in the bad old days some of us used to hang a 2W non-inductive resistor across the antenna or coax connections.  This bleeds of precipitation or wind caused static and hopefully saved equipment from close-by lightning strikes.  
We also used gas tube voltage limiters for additional protection.  Probably 
nothing would save equipment from a direct strike.

Arv  K7HKL
_._


On Sun, Aug 23, 2020 at 11:30 AM Rob French (KC4UPR) <kc4upr@...> wrote:
Clark,

Thanks!  I'm going to file that under, "Duh... why didn't I think of that..."  I suspect I won't be able to source the exact part, but I see the parameters printed on the tops of the relays, so I'll examine them and find something comparable from Mouser.

Bob/Arv,

Yep, that's essentially what I'm looking to do.  Just would be using a relay so that I can automate the process when I turn off the tuner.  My goals with this arrangement are:

(1) If I disconnect the antenna for lightning safety, and forget to plug it back in, I can have it default to "dummy load" when it starts up, so that there is always something good connected to the rig.

(2) If I forget to disconnect the antenna for lightning safety, at least there is some alternate path to ground for any discharges, that don't go through my rig.  (I realize this won't save me from a direct hit, but perhaps from whatever recent discharge killed the TX on another of my rigs... no lightning strike to the house that I'm aware of, but killed a diode in my tuner, killed the TX output of the other rig, and killed the rig's external power supply...)   I think I would need a DPDT relay in this case, or maybe two relays, to (a) automatically switch the rig to the dummy load, and (b) switch the antenna to ground.

Thanks again for the input!

-Rob KC4UPR


Jack, W8TEE
 

I remember seeing a picture in QST of the back of a two story, white, house that looked like someone had taken a black Magic Marker and draw a perfect straight 6' line on the second floor, then a 90 degree angle towards the ground, then about 3' about the yard it made another right angle and ran in a perfectly straight line to the other edge of the back of the house.

The "black line" was actually where the wood siding was blown off the house when the water in the water supply piper turned to super heated steam when a lightning strike hit the antenna tower which the owner had grounded to the second floor water pipe. If looked like a flattened, 4" wide, perfectly cut, Mark of Zorro across the back of the house. If Ben had seen that house, he wouldn't have been flying kites in an electric storm!

Jack, W8TEE

On Sunday, August 23, 2020, 9:35:07 PM EDT, Bob Lunsford via groups.io <nocrud222@...> wrote:


Speaking of the power of lightening, I had a repeater up in central Texas for about three years. I had a 1/4 wave vertical at 50-ft for the receiver and a 1/4 wave vertical at 30-ft on the same tower mounted upside-down and used root beer can cavities (four of them) and the repeater worked fine. Made with VHF Engineering kit boards. Was a local repeater designed for about a 15-20 mile radius in the Killeen-Fort Hood area.

Once when a warning about a tremendous thunder storm was almost on top of us, I disconnected the antennas. I left the BNC connector hanging about six inches away from the repeater and when across the room at the time of the storm, I kept hearing some snapping sounds and looked at the transmitter antenna (about halfway up the tower) and saw sparking about every second or so. This meant that there was at least a voltage of about 2800 volts on the antenna, across the ground. From then on, when I disconnected the antenna, I also plugged it into a shorted connector to "bleed off" the charge.

To save our radios, this should be kept in mind if we need to disconnect for a storm. The antennas connectors also need to be shorted out. Some antenna switches do this by design and, for me, are worth the extra dollars to get one. If, on the other hand, lightening does strike, there is enough energy involved that nothing short of grounding everything will keep damage to a minimum.

I saw a TV antenna had been hit by lightening and the stroke came down the twinlead and entered the floor seeking the concrete base underneath. Tore up the carpet for about ten feet. Surprised to find that the TV was still working. The lightening had bypassed the TV and jumped from the twinlead straight to the floor. The bend in the twinlead saved the TV.

I live in a stormy area and hams in the KY, OH, WV and TN areas pull the plug when storms come in. Too many of them regret not doing so in the past. We must consider our uBITX radios and their antennas equally prone to damage in case of a lightening strike.

Bob — KK5R

On Sunday, August 23, 2020, 3:45:27 PM EDT, Arv Evans <arvid.evans@...> wrote:


Rob KC4UPR

Back in the bad old days some of us used to hang a 2W non-inductive resistor across the antenna or coax connections.  This bleeds of precipitation or wind caused static and hopefully saved equipment from close-by lightning strikes.  
We also used gas tube voltage limiters for additional protection.  Probably 
nothing would save equipment from a direct strike.

Arv  K7HKL
_._


On Sun, Aug 23, 2020 at 11:30 AM Rob French (KC4UPR) <kc4upr@...> wrote:
Clark,

Thanks!  I'm going to file that under, "Duh... why didn't I think of that..."  I suspect I won't be able to source the exact part, but I see the parameters printed on the tops of the relays, so I'll examine them and find something comparable from Mouser.

Bob/Arv,

Yep, that's essentially what I'm looking to do.  Just would be using a relay so that I can automate the process when I turn off the tuner.  My goals with this arrangement are:

(1) If I disconnect the antenna for lightning safety, and forget to plug it back in, I can have it default to "dummy load" when it starts up, so that there is always something good connected to the rig.

(2) If I forget to disconnect the antenna for lightning safety, at least there is some alternate path to ground for any discharges, that don't go through my rig.  (I realize this won't save me from a direct hit, but perhaps from whatever recent discharge killed the TX on another of my rigs... no lightning strike to the house that I'm aware of, but killed a diode in my tuner, killed the TX output of the other rig, and killed the rig's external power supply...)   I think I would need a DPDT relay in this case, or maybe two relays, to (a) automatically switch the rig to the dummy load, and (b) switch the antenna to ground.

Thanks again for the input!

-Rob KC4UPR


--
Jack, W8TEE