Carl-NC
Active member
In the Sensitivity screen V3 reports a recommended gain setting for the preamp. Someone recently asked if holding the loop in the air should result in a recommended gain of 15. My initial answer was 'yes', but after discussing this with the engineering team it is not so simple.
V3 looks at the "residual" receive signal to come up with the recommended preamp gain. Residual signal can either be loop null, ground signal, or both. Sometimes the addition of ground can cancel loop null for a lower overall residual signal. Sometimes it adds for an overall worse residual signal. EMI can also affect the residual signal.
V3 wants to keep the total residual signal level below 10% so it recommends a preamp gain to do that. However, 10% is a rather arbitrary level. We could have made it 20%, or 30%. I almost always run my V3 at several notches above the recommended preamp gain, because there is no real harm in doing so as long as there is sufficient headroom left to detect. What is sufficient? Realistically, you could probably go as high as 50%, but I would back off to no more than 30-40%.
Quite often EMI will be the limiting factor. When testing in my noisy office, I can get a recommended gain of 11 but can only run at about 3 to keep it stable. So in cases where EMI is the limiting factor, run the preamp gain as high as you can. Keep in mind that EMI-induced falsing can also be reduced by lowering the DISC sensitivity, and often this is a better way to reduce EMI falsing than lowering the preamp gain. Also, when EMI limits the max gain TX boost becomes an effective way to get some extra depth.
So there is still the question of what a good loop should look like. Ideally, a perfect loop will give a recommended gain of 15 in the air, but that is not a necessary condition to call a loop "good". The D2 loops are coming out of the factory with extremely good nulls, but over time they can shift slightly, resulting in a null that may give a recommended gain of less than 15. The Eclipse 5.3 are being manufactured to exactly the same specifications of the D2, but on a V3 they pretty consistently give a recommended gain of 10 or so.
As I've explained, this is based on a target residual of 10% and there is no real need to run this low. You can easily run a loop that has a recommended gain of 8 all the way to 15 with no problem. Replacing such a loop with a more perfect loop would not offer any performance difference. Therefore, White's will consider any loop that results in a recommended gain of 8 or more in air to be a good loop.
- Carl@White's
V3 looks at the "residual" receive signal to come up with the recommended preamp gain. Residual signal can either be loop null, ground signal, or both. Sometimes the addition of ground can cancel loop null for a lower overall residual signal. Sometimes it adds for an overall worse residual signal. EMI can also affect the residual signal.
V3 wants to keep the total residual signal level below 10% so it recommends a preamp gain to do that. However, 10% is a rather arbitrary level. We could have made it 20%, or 30%. I almost always run my V3 at several notches above the recommended preamp gain, because there is no real harm in doing so as long as there is sufficient headroom left to detect. What is sufficient? Realistically, you could probably go as high as 50%, but I would back off to no more than 30-40%.
Quite often EMI will be the limiting factor. When testing in my noisy office, I can get a recommended gain of 11 but can only run at about 3 to keep it stable. So in cases where EMI is the limiting factor, run the preamp gain as high as you can. Keep in mind that EMI-induced falsing can also be reduced by lowering the DISC sensitivity, and often this is a better way to reduce EMI falsing than lowering the preamp gain. Also, when EMI limits the max gain TX boost becomes an effective way to get some extra depth.
So there is still the question of what a good loop should look like. Ideally, a perfect loop will give a recommended gain of 15 in the air, but that is not a necessary condition to call a loop "good". The D2 loops are coming out of the factory with extremely good nulls, but over time they can shift slightly, resulting in a null that may give a recommended gain of less than 15. The Eclipse 5.3 are being manufactured to exactly the same specifications of the D2, but on a V3 they pretty consistently give a recommended gain of 10 or so.
As I've explained, this is based on a target residual of 10% and there is no real need to run this low. You can easily run a loop that has a recommended gain of 8 all the way to 15 with no problem. Replacing such a loop with a more perfect loop would not offer any performance difference. Therefore, White's will consider any loop that results in a recommended gain of 8 or more in air to be a good loop.
- Carl@White's
