Deaf RX after strong near RF Field
Jiri Culak
Good morning very (unfortunate one)
I happened to transmit today with a full legal limit power and suddenly realise that my Hermes lite2 latest build doesn’t receive anymore going over 20 dB in LNA causes a receiver overdrive I tested transmission and that works 100%
But I don’t like us a funny smell close to the relay and I found that the diode D1 Is short circuit. What I also found is when I transmit what’s another radio I can hear or see my signal on waterfall obviously very attenuated.
I am so sad I have not turned the Hermes off while using another radio. No I would like to ask the group for any help in diagnosing what could be at fault and how shall I proceed. Or even if I fail if there would be anybody friendly around who would help me out looking into it for me.
Tnx
Jiri
PS: It's afternoon and I have made some progress:
I had to remove D1 (the Zener/back to back clamping diode) which was indeed shorted and I also found that L11 has been open circuit. I couldn't find replacement parts so for now I had left the Hermes for test without D1 and I replaced L11 with a 800nH SMD inductor I found laying around - I didn't want to just bridge the L11. anyway the result is:
I can hear stuff to sort of simillar levels apart from 144MHz (28MHz IF) as I have still another symptom and that is when I go with RFLNA gain above 19dB, it goes into self-osculation of sorts.
May I ask what this could be? I saw this behaviour with D1 being still shorted so I wonder if I had a A/D port knackered or if this could be the RX isolation tansformer being at fault?
I found the culprit - I have a antenna switch for SO2R and unfortunatelly main relay, which goes to short the HL2 Antenna port when another radios are in use with the shared antennas so HL2 Stayed connected to 160m TX antenna while 80m TX has been in operation. Can I ask for assistance please?
Steve Haynal
Jiri C
Hello Steve
I had a look at the HL2 first and as I mentioned I smelled something so visual inspection showed D1 being somewhat cracked, looking at schematics revealed it’s a protection diode like those used for ESD protections / this one seemed like two zeners and two blocking in one package, so anyway I desoldered it using hot air and measured – and it indeed had been shot and was shorted.
Now I had removed it and also found that L11 to be open circuit, so I couldnt find 0.33uH inductor and from my memory it’s somethin like 2x2mm air core with 3 turns so not much of inductance.?
I hound a as close as possible 2uH to test, and dropped it in and RX came back to live BUT – RX isn’t 100% correct. As mentioned further down – LNA Setting wont go beyond 15-19dB otherwise it goes to RX / ADC overload. I am now suspecting perhaps D1 needing to be there or T2 8:1 transformer to be shot as well. If impedance isn’t matched at RX+ / RX - side of the AD9866 this could result in simillar behavior? Also I found that I only hear to about 7 MHz, after that all seems like I had an 30dB ATT inserted. Maybe its because the LNA not allowing to go higher settings or who knows. (I bypassed the N2ADR BPF to rule that out).
Any thoughts will be appreciated.
Thanks a lot
Jiri
Sent from Mail for Windows
From: Steve Haynal
Sent: Monday, November 14, 2022 6:48 AM
To: Hermes-Lite
Subject: Re: Deaf RX after strong near RF Field
Hi Jiri,
Sorry to hear of your unfortunate experience. How do you know D1 is shorted? A ohm meter will measure a short in circuit because of T2. If D1 is really shorted, you can remove it and retest the receiver. The receiver should work without D1. D1 is there to protect against very strong signals.
73,
Steve
kf7o
On Sunday, November 13, 2022 at 9:08:17 AM UTC-8 m0i...@gmail.com wrote:
Good morning very (unfortunate one)
I happened to transmit today with a full legal limit power and suddenly realise that my Hermes lite2 latest build doesn’t receive anymore going over 20 dB in LNA causes a receiver overdrive I tested transmission and that works 100%
But I don’t like us a funny smell close to the relay and I found that the diode D1 Is short circuit. What I also found is when I transmit what’s another radio I can hear or see my signal on waterfall obviously very attenuated.
I am so sad I have not turned the Hermes off while using another radio. No I would like to ask the group for any help in diagnosing what could be at fault and how shall I proceed. Or even if I fail if there would be anybody friendly around who would help me out looking into it for me.
Tnx
Jiri
PS: It's afternoon and I have made some progress:
I had to remove D1 (the Zener/back to back clamping diode) which was indeed shorted and I also found that L11 has been open circuit. I couldn't find replacement parts so for now I had left the Hermes for test without D1 and I replaced L11 with a 800nH SMD inductor I found laying around - I didn't want to just bridge the L11. anyway the result is:
I can hear stuff to sort of simillar levels apart from 144MHz (28MHz IF) as I have still another symptom and that is when I go with RFLNA gain above 19dB, it goes into self-osculation of sorts.
May I ask what this could be? I saw this behaviour with D1 being still shorted so I wonder if I had a A/D port knackered or if this could be the RX isolation tansformer being at fault?
I found the culprit - I have a antenna switch for SO2R and unfortunatelly main relay, which goes to short the HL2 Antenna port when another radios are in use with the shared antennas so HL2 Stayed connected to 160m TX antenna while 80m TX has been in operation. Can I ask for assistance please?
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Jiri C
Hello again all
I spent some time on the HL2 and it seems like unfortunate situation.
So I checked and T2 seems ok (continuity / visual) and so does the 0.1uF and all the component around the RX path.
I still can not hear very well on higher bands and I still can not go with GAIN above 19dB, sometimes even less than that and I found out that AF9866 is running a bit hot. I am not sure how hot it should be running but it is hot. So have I burned my ADC? Interesting is that it does receive, it is just slightly deaf on high bands and at LNA level 12-13 I get 75% dynamic range reached and at 19-20 it gets overload.
Any ideas what this could be?
Tnx
Sent from Mail for Windows
From: Steve Haynal
Sent: Monday, November 14, 2022 6:48 AM
To: Hermes-Lite
Subject: Re: Deaf RX after strong near RF Field
Hi Jiri,
Sorry to hear of your unfortunate experience. How do you know D1 is shorted? A ohm meter will measure a short in circuit because of T2. If D1 is really shorted, you can remove it and retest the receiver. The receiver should work without D1. D1 is there to protect against very strong signals.
73,
Steve
kf7o
On Sunday, November 13, 2022 at 9:08:17 AM UTC-8 m0i...@gmail.com wrote:
Good morning very (unfortunate one)
I happened to transmit today with a full legal limit power and suddenly realise that my Hermes lite2 latest build doesn’t receive anymore going over 20 dB in LNA causes a receiver overdrive I tested transmission and that works 100%
But I don’t like us a funny smell close to the relay and I found that the diode D1 Is short circuit. What I also found is when I transmit what’s another radio I can hear or see my signal on waterfall obviously very attenuated.
I am so sad I have not turned the Hermes off while using another radio. No I would like to ask the group for any help in diagnosing what could be at fault and how shall I proceed. Or even if I fail if there would be anybody friendly around who would help me out looking into it for me.
Tnx
Jiri
PS: It's afternoon and I have made some progress:
I had to remove D1 (the Zener/back to back clamping diode) which was indeed shorted and I also found that L11 has been open circuit. I couldn't find replacement parts so for now I had left the Hermes for test without D1 and I replaced L11 with a 800nH SMD inductor I found laying around - I didn't want to just bridge the L11. anyway the result is:
I can hear stuff to sort of simillar levels apart from 144MHz (28MHz IF) as I have still another symptom and that is when I go with RFLNA gain above 19dB, it goes into self-osculation of sorts.
May I ask what this could be? I saw this behaviour with D1 being still shorted so I wonder if I had a A/D port knackered or if this could be the RX isolation tansformer being at fault?
I found the culprit - I have a antenna switch for SO2R and unfortunatelly main relay, which goes to short the HL2 Antenna port when another radios are in use with the shared antennas so HL2 Stayed connected to 160m TX antenna while 80m TX has been in operation. Can I ask for assistance please?
--