Re: Drive remote dual coil latch relay with single RF
i just looked at the eneloop batteries.
So I calculate with estimateed data. 2000mAh capacity, 90% charge after one year.
This means 10% discharge in 365*24h = 200mAh / 8760h = 22.8 uA
This is 2280 times the bjt current.
Klaus
Very informative! So no need for a bare relay.
Initially, there were two ways to accomplish the purpose as described in this thread.
One way was the "delay" whereas the other was the "frequency".
I am thinking of a third way and this is the "power level" way. This could work without tricky filters. Can you think of any way to passively detect the power level (be it on the RF part or after rectification) and decide which coil to energize?
Hi,
i don′t think it is a good idea. Any change in antenna, direction, distance, transmitter power (bad battery?) may lead to wrong switching.
To make it more secure, i′d go for sending data (UART style). A small (maybe 8 pin PIC or AVR) uC can
* check if code is correct (to prevent wrong switching at all)
* decide to switch ON
* decide to switch OFF
And low RF power should be no problem.
That′s a more intelligent solution, but also a higher effort solution. And it needs additional power. With intelligent sleep and wake up it may be low enough.
Klaus
Hi, I think I did it.
The solution is much simpler, no need for any diplexers or frequency depended components and micros.
It uses the previously unused contacts of one of the two relays.
Assuming S1b is at the position shown, a TX pulse will switch the bottom 2222, which switches S1a but also toggles S1b to switch to the top 2222 for the next pulse. A next TX pulse will reverse the situation.
I have also removed the charge pumps and replaced them by a BAT54, which has much lower voltage drop. In this configuration the 2222's can be switched nicely at low TX powers (tested).
I have also removed the relay diodes, as I did not find them neccessary. The relays never kicked back, maybe it has to do with the latch relays that have coil polarities, I do not know. However it worked perfectly ok without these diodes.
The 30MHz LPF is still found to be useful, but I have not tested this in impedances other than 50R, because I to not know the impedance of the antenna whip and the impedance of the preamplifier output. Any guess would be useful.
I also consider the mmbt4401.
In the datasheet an emitter cot off current is not specified, however a collector cut off current is 0.1uA, whereas on the mmbt2222 it is 10uA.
So is the mmbt4401 better in that sense for lower power consumption when switched off?
Hi,
Mmbt4401 datasheet,
Look at figure7. This is the current when V_BE = 0.
Klaus
Just to confirm I am reading this right. Is this 0.4-0.5nA at 25C?
Hi,
We both read the same...
from my post#19:
Klaus
Hi I have tested the circuit of post #24 but there is a problem.
The relay continuously oscillates between it's two positions. This is because the RF pulse that comes in is maintained even after the relay is switched (even a fast TX creates multiple pulses), which causes the relay to switch again and so on...
So to correct the problem, I need a way to create a single pulse out of a continuous RF. In other words, when the RF comes in, a single pulse is created.
Any ideas?
I have tried a simple series capacitor but it did not work of course because it can pass RF all the time.
Or there might be a way to delay this action of the relay?
A capacitor across the relay contacts maybe?
Or a capacitor from the 4401 base to the ground, to delay it's switching?
Why do you create a complicated switching solution, instead of a simple passive diplexer? That would route the RF range to the RF antenna, and the VHF/UHF range to the VHF/UHF antenna. Simple hardware, no manual switching needed, no power supply needed.
I have to say I do not understand the question. The whole point is to have the RF switch power to the preamplifier and bypass it and at the same time this circuit must consume no power when no switching action occurs (to save battery life).
A diplexer solution would theoretically work (shown previously) and the antenna can be switched to ON by transmitting for a moment on vhf and then to OFF by transmitting for a moment to uhf (or vice versa).
However the schematic on post #24 works without a diplexer and it is much simpler and does not require a dual band transceiver at all, so it is more general. It is just that the circuit oscillates continuously between the two relay positions, because the applied RF is longer in duration (a momentary button activated TX, or PTT as hams call it) than the relay response. The relay switches, but the RF is still at the input, so the relay switches again and again and so on...
I believe a simple delay mechanism (a capacitor placed somewhere) will correct this.
I am thinking of a capacitor at the 4401 base to ground but I may have to alter the bat54 to a series configuration to charge the capacitor, rather than a shunt.
Any ideas are welcome.
I didn't realize that your preamp works from battery, and you want to be able to switch it off for power saving. Otherwise, I would just use the diplexer with no RF switch at all.
I feel that this is counter-intuitive solution that requires some transmit operation by the user to switch the antenna band. Can be done, but it feels unnecessarily complicated in use and design. I would replace the entire switch by a simple diplexer that separates RF band from the other bands: passive, no manual switching needed.
(Note on your dualband comment: I didn't suggest to use dual bands for switching your relay. I suggested to use no relay at all, and separate the RF bands passively with the diplexer. The only disadvantage is that your RF preamp would be always ON, consuming power. )
Of course that is the whole point.
The HF preamplifier must be switched on/off only from the transceiver signal (the only available signal with no modifications to the transceiver).
When off, power to the preamp is off and it is bypassed, so only the passive antenna operates.
The only power-free solution I have found is the latch relay, well discussed above.
Switching can be done with the complex diplexer, or by the scheme on post #24. I consider this as a simpler solution, since there are already free relay contacts. But I mentioned what the problem is.
Well, you have a trend towards the most complex solutions for the most simple problems. A much more elegant solution would be to power (and switch) the setup through the coax cable, with a simple bias tee at the antenna cable.
That doesn't require a modification to the transceiver, avoids battery use and avoids the crazy operating scheme of transmitting to switch the receive range.
I think you have not understood the situation, unless I am missing something.
As explained in previous posts, the active antenna is a rubber antenna that is used on top of a handheld V/U transmitter with a wide (HF) RX coverage.
How would you power the antenna without modifying the transceiver? Batteries must be contained inside the antenna and the antenna has to be switched from the transmitter signal (thought it to be more elegant and low profile than using a hand switch on the antenna).
As said the diplexer solution can work, but I was looking for a more simple/frequency independent alternative, like shown in post #24.
I mentioned what was the problem with this switching scheme and I believe a delay mechanism (capacitor charging?) can solve this.
Any comments are welcome.
I was assuming you need something for remote operation.
If you want to use it directly at the handheld transceiver, as in the PDF that you attached, a simple mechanical switch seems best/easiest to me. Unlike switching with RF signals, it is intuitive and you see what the switch position is.
I was thinking of remote operation, with a cable between transceiver and antenna. Then it would be easier to feed DC for supply and switching through the cable, and just insert a little DC/RF splitter ("bias tee") in the shack between transceiver and antenna cable.