mcHF V06 TX-RX relay antenna switching as implemented by Wolfram PY2BND
Related post: https://ea8arx.blogspot.com/2018/06/tx-rx-antenna-switching-pin-diodes-vs.html
When I had to make the modification of my mcHF V06, due to the breakage of a pin diode in the antenna switching circuit, I forgot to document with photographs -step by step- the modifications that had to be made on the RF board. At the time I thought my explanations were enough. Although I was able to personally comment with Chris M0NKA on the modification I had to make as I did not have a replacement for the PIN diode quickly, I had no response from any other radio amateurs who would have carried out the modification.
Until Wolfram Perrey, PY2BND, contacted me from Brazil asking for details of the implementation. In his case he wanted to carry it out to improve the transmission signal. Before continuing, I must add that Wolfram is a very qualified engineer who would not have needed my additional explanations to carry out the modification, but Wolfram had the idea of doing what I did not do: document with photographs the details of the implementation of the modification proposed by me. Additionally, Wolfram found that it increased power in the low bands by removing the C78 capacitor that was unnecessary after modification.
This proposal is from Wolfang PY2BND and works for V0.6 PCBs. All photographs are of him. Please note that Wolfram used a different signal double relay than the one I used; TQ2SA-5V from PANASONIC instead of G6S-2F-Y from OMROM.
Wolfang's implementation, except for the fact that he used a different signal relay, is almost identical to the modification I implemented on my two mcHF SDR Transceivers.
Wolfram expressly authorized me to publish the photographs of his implementation, making express mention of the following points, which I will reproduce literally.
"Yes, I would be very happy if You place the implementation of Your proposal in Your blog. It would make the implementation so much easier for people who are looking into Your blog. May be You only mention on the HW picture and the mod instruction that this proposal is from me and that it works for V0.6 PCBs. (Because I do not know how the other PCB versions look like)
I guess, the way I did it is low invasive and easy to do. And please, explain what is the real difference of Your design, the way You proposed it from others:
1 - Mention that the high side switching of the relay must be done by a PNP transistor.
2 - That switching transition between RX and TX is done the way that the RX band-pass is completely disconnected and grounded before any RF power from the PA can go into the LPF. This way no blowing up RX Bandpass circuit can ever happen independent of the switching speed of the relay or a complete failing Relay. That the circuit from You is the only safe one!
3 - That on RX operation band-pass is directly connected to the LPF but with PA is disconnected and does not hang any more on the RX path during receive operation.
I would like to say once again thank You for Your proposal that You placed in Your blog. If You complete it with the hints to implement it make the modification very easy and safe.
Please feel free to asks for more details or or better pictures if needed. I also modified my mod document with the coax cable and how to connect the shielding in the PCB. Please feel free to make full use of the attached document. "
Wolfram insisted on two details:
"Please make sure to use shielding coaxial cable in the power feeding part of the circuit. The use of open wire will cause a unstable and oscillating PA stage due to RF Feedback into the amplifier circuit".
Well, this is how I fulfill Wolfang's excellent work. I have to add, in addition, that Wolfang eliminated the C78 capacitor replacing it by a jumper. That improved the output power by 160 - 80 meters. This capacitor is mandatory to block the DC component when using PIN diodes, but with relay antenna switching is unnecessary. I have never operated in the 160 meter band, basically because I do not have an adequate antenna and the mcHF does not have specific low pass filters for that band. Chris M0NKA suggests using it at your own risk.
The fact that there is another capacitor C81 of a value 100 times higher than C78, suggests a BOM error. Both capacitors can be eliminated and replaced by zero ohm resistance if relay antenna switching is implemented. There is still a third capacitor C1 in series. This capacitor is necessary to block the direct voltage biasing pin 7 of U1 (Pass-band filter switch).
In summary: I have been very happy to learn that in the midst of the global pendemic, someone, on the antipodes of the planet, took into account my modest contribution to improve the design of the mcHF. I was just trying to share ideas.
PDF DOCUMENT
Until Wolfram Perrey, PY2BND, contacted me from Brazil asking for details of the implementation. In his case he wanted to carry it out to improve the transmission signal. Before continuing, I must add that Wolfram is a very qualified engineer who would not have needed my additional explanations to carry out the modification, but Wolfram had the idea of doing what I did not do: document with photographs the details of the implementation of the modification proposed by me. Additionally, Wolfram found that it increased power in the low bands by removing the C78 capacitor that was unnecessary after modification.
This proposal is from Wolfang PY2BND and works for V0.6 PCBs. All photographs are of him. Please note that Wolfram used a different signal double relay than the one I used; TQ2SA-5V from PANASONIC instead of G6S-2F-Y from OMROM.
Wolfang's implementation, except for the fact that he used a different signal relay, is almost identical to the modification I implemented on my two mcHF SDR Transceivers.
Wolfram expressly authorized me to publish the photographs of his implementation, making express mention of the following points, which I will reproduce literally.
"Yes, I would be very happy if You place the implementation of Your proposal in Your blog. It would make the implementation so much easier for people who are looking into Your blog. May be You only mention on the HW picture and the mod instruction that this proposal is from me and that it works for V0.6 PCBs. (Because I do not know how the other PCB versions look like)
I guess, the way I did it is low invasive and easy to do. And please, explain what is the real difference of Your design, the way You proposed it from others:
1 - Mention that the high side switching of the relay must be done by a PNP transistor.
2 - That switching transition between RX and TX is done the way that the RX band-pass is completely disconnected and grounded before any RF power from the PA can go into the LPF. This way no blowing up RX Bandpass circuit can ever happen independent of the switching speed of the relay or a complete failing Relay. That the circuit from You is the only safe one!
3 - That on RX operation band-pass is directly connected to the LPF but with PA is disconnected and does not hang any more on the RX path during receive operation.
I would like to say once again thank You for Your proposal that You placed in Your blog. If You complete it with the hints to implement it make the modification very easy and safe.
Please feel free to asks for more details or or better pictures if needed. I also modified my mod document with the coax cable and how to connect the shielding in the PCB. Please feel free to make full use of the attached document. "
Wolfram insisted on two details:
"Please make sure to use shielding coaxial cable in the power feeding part of the circuit. The use of open wire will cause a unstable and oscillating PA stage due to RF Feedback into the amplifier circuit".
"Relay OMRON G6S-2F DC5 and
PANASONIC-TQ2SA-5V
has been proven as very reliable candidates with good RF characteristics. Nerveless there are many outer similar and well working relays on the market. So, when selecting a different type please take care on similar basic characteristics, means: small size, low profile,
single-side stable, 5V and similar contact layout, low insertion loss, around 6ms switching time and good mechanical and electrical reliability and lifetime. It has also been verified that the relay modification does not cause "clicking" on the CW carrier.
The findings where that the relay contact is always been closed before a smooth CW carrier envelope happens, means
that no CW carrier clicking happens. This verification has been done
with a "TX mute" setting to 0 ms (mcHF configuration).
The specifications of both suggested relays claims a expected life time of 2×10^5 cycles, under load. Never less the relay switching occurs load-less expanding the minimum expected operations cycles well beyond
2×10^5 to a value probably more close to mechanical lifetime of 10^8 cycles. So, looking from a practical standpoint there are very little concerns to use the suggested relay switch regarding life time and CW carrier quality even under more demanding QRK setting of the mcHF."
The fact that there is another capacitor C81 of a value 100 times higher than C78, suggests a BOM error. Both capacitors can be eliminated and replaced by zero ohm resistance if relay antenna switching is implemented. There is still a third capacitor C1 in series. This capacitor is necessary to block the direct voltage biasing pin 7 of U1 (Pass-band filter switch).
In summary: I have been very happy to learn that in the midst of the global pendemic, someone, on the antipodes of the planet, took into account my modest contribution to improve the design of the mcHF. I was just trying to share ideas.
PDF DOCUMENT
Thanks for redirecting me to this Alvaro, I will add this to my build for a new 0.5 I'm building for my group, it has been on hold for a long time! My own mcHF has terrible QRM over 4 watts, so I guess I will tear it apart too.
ReplyDelete73
The photos were contributed by Wolfram Perrey, PY2BND, he implemented my proposal and was kind enough to take the photos that I did not take at the time. He also tested the modification and found that it worked as expected.
ReplyDeleteYes, it's working fine, I have added it to my new build.
ReplyDeleteI have been testing this modification for two years on two different teams. It is a very solid modification, improves reception by isolating the antenna from the secondary of the T3 transformer and increases the linearity of the emitted SSB signal. I'm glad it worked for you OK. A greeting.
ReplyDelete73's and Health!
Hello Alvaro! My switch is in now for a Year and it works until today perfect. Never failed and I never was in since then. This is a switch idea from You is a circuit that rely works!! Makes grate signal as well, no distortion!! PY2BND - 73!!
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