20-05-2018, 11:28 AM
I had the need to switch my radio to three different transverters and I didn't want to swap cables. In my junk box was a pair of SPDT BNC relays with 28V coils.
What a frustration! I wanted these relays for portable operation and that limited me to a nominal 12V supply. I could have used one of those $2 SMPS PCB's ubiquitous on eBay but they do make a bit of noise in the VHF/UHF range so I ruled them out.
Then I found an article by KO4BB. This was the answer I was looking for. The circuit is quick to lash up on vero board and in my case it worked as advertised. To conserve current drain the circuit is arranged so there is only ever one relay on at a time. As it turns out these relays only pull 50mA so unlikely to cause any problem. As a bonus the circuit works reliably to below 11 volts.
I wanted to see how fast I could switch a relay on and off with this arrangement and it was pretty good. If I switched really fast there was not enough time for the capacitor to fully charge and the relay would not pull in. However, it is unlikely that you could key your PTT that fast on a regular basis so I think you could quite safely use this circuit to drive the main change over relay in a transverter.
Here's a look at my test setup.
Retuning a 5 pole 2.7GHz filter salvaged from some old OB gear.
My aim was for minimum loss at 2403MHz and maximum rejection of the 2m IF product.
Result is insertion loss is less than 1dB at 2403MHz and better than 15dB at the point that a 145MHz IF may appear. Obviously a 70cm IF would make things easier.
The test gizmo is a TPI-Link 1001B and has changed the way I do things in the shack.
What a frustration! I wanted these relays for portable operation and that limited me to a nominal 12V supply. I could have used one of those $2 SMPS PCB's ubiquitous on eBay but they do make a bit of noise in the VHF/UHF range so I ruled them out.
Then I found an article by KO4BB. This was the answer I was looking for. The circuit is quick to lash up on vero board and in my case it worked as advertised. To conserve current drain the circuit is arranged so there is only ever one relay on at a time. As it turns out these relays only pull 50mA so unlikely to cause any problem. As a bonus the circuit works reliably to below 11 volts.
I wanted to see how fast I could switch a relay on and off with this arrangement and it was pretty good. If I switched really fast there was not enough time for the capacitor to fully charge and the relay would not pull in. However, it is unlikely that you could key your PTT that fast on a regular basis so I think you could quite safely use this circuit to drive the main change over relay in a transverter.
Here's a look at my test setup.
Retuning a 5 pole 2.7GHz filter salvaged from some old OB gear.
My aim was for minimum loss at 2403MHz and maximum rejection of the 2m IF product.
Result is insertion loss is less than 1dB at 2403MHz and better than 15dB at the point that a 145MHz IF may appear. Obviously a 70cm IF would make things easier.
The test gizmo is a TPI-Link 1001B and has changed the way I do things in the shack.