Strange new issue with ADC overloading

[Ron Lewkowicz]

Since yesterday I seem to be having a problem with the ADC lights coming on when they should not be. To get them to go out now gain must be reduced all the way to -12.  By about -8 to -5 both the 75 and 100 are on full time.  The HL2 still transmits fine and receive seems to still want the gain set to at least 10-15.  The S meter would seem to be reading about 20dB too high now as well.  Happens with all antennas and on all bands.  I can hear the LPF relays clicking OK as I change bands.  Quisk, SparkSDR, piHPSDR and deskHPSDR  all the same.  Radio is about two years old.

Hoping someone could point me to possible items on the board that might cause this and where to test for the problem.  I'm not much of an electronics wizard but should be able to repair something like a blown resistor or capacitor. That's sort of what I'm thinking might be the cause but I'll need help figuring out which part of the board to look at.  

Thanks for taking the time to read this.

VE6RLZ

[DL1YCF]

Do the ADC lights come during RX or TX?

If it is during RX, that is really strange. If it is during TX,
the T/R relay may produce too much cross-talk.

> --
> You received this message because you are subscribed to the Google Groups "Hermes-Lite" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to hermes-lite...@googlegroups.com.
> To view this discussion visit https://groups.google.com/d/msgid/hermes-lite/f0545139-a125-4eb4-8070-17c080cf0f35n%40googlegroups.com.

[John Shoffner]

I see this as well, from time to time. Receive only. Have paid much attention during xmt. I starts  as an intermittent thing.  I generally just try reducing AGC or add rx attenuation.  It eventually stops.  I remain curious.

[ron.ni...@gmail.com]

One possible cause of seeing ADC overload with a normal gain setting is that the high pass filter isn't working and the antenna is picking up a strong AM broadcast band signal. This could be either be due a software misconfiguration, or a failure of the high pass filter relay.  You can check this by testing receive with an outboard broadcast band rejection filter.  Another possibility is that someone or something nearby is generating a strong shortwave band signal, possibly outside the ham bands.  73, Ron, n6ywu

[Ron Lewkowicz]

Thank you for your comments.

This is RX only. When I TX the lights go out.  The nearest AM broadcast is about 60 miles away and not particularly strong.

Remembered finally to turn off NB2 and I do see now there is incredible noise.  40m S9+5-10.  80m S9+25  this is across  entire bands. This is new.  WWV at 10Mhz sounds like an arc welder.  However, on bands like 10m which are much quieter, although now also much noisier than I had before, I still see the same issue.  I gather though that the noise problem on the lower bands might still cause this? 

I've swapped power supplies, changed computers, bypassed my tuner with no effect and it's with both my antennas.

Next plan I guess is to bring in a battery to run everything and switch off the main breaker for the whole yard at the pole.  After that I guess make up a portable setup and go try somewhere where there are no power lines.

The HL2 is the only HF transceiver I have so can't swap that out.

[Tim Thorson]

I have always had something similar -  all my RX signals are huge between S8 and plus 20 - like I can't really give true signal reports. I see high levels above waterfall,  However no strong trails are coming down, just normal - Other than that everything works fine and I haven't thought much about it.

At first, I did not have this issue, because I was first using HL2 as an SDR receiver (like RTLSDR dongle) Because, I was waiting for my amp.  In this RX configuration I was using HL2's receive SMA input only with loop on the ground - This gave me excellent clear clean signals & very low noise, good s/n...   

Then I finally got my mercury 3S amp and Palomar EFHW, When I got it all implemented, I then noticed noise/signals were very high. It was not an issue, everything worked fine - I always said, someday I'll get this calibrated...  leaving the loop on the ground plugged in on the RX input, signals get overwhelmed when I have the EFHW (TX) plugged in ... I haven't figured out yet about having RX JUST from the loop on the ground as receive-only and the Palomar EFHW as transmit only.. I remember somebody saying that this was a possible, but I don't know how yet. . Would think this as the most ideal situation

 

Tim KD6HOF

To view this discussion visit https://groups.google.com/d/msgid/hermes-lite/3792d63f-67cc-40f1-b1ea-c3a5949fa810n%40googlegroups.com.

[Ron Lewkowicz]

If I push the gain up to maximum then the noise goes away and I can hear stations well but of course the ADC lights have been on full since 0. 

[James Ahlstrom]

Change to the Band Scope in your SDR software. It will show all the received spectrum and you can look for strong signals.

Jim

N2ADR

[Ron Lewkowicz]

Great suggestion. Thank you Jim.  Definitely looks like a lot going on between 2-4Mhz  at the moment.  

I live on a farm with no really close neighbours.  Solar is not a big thing here and I haven't noticed anything new go up. Rural power lines are generally the culprit with bad insulators.  The HL2 seems to work OK other than the ADC lights come on full as soon as you try to add any LNA gain. I just don't know if that means an issue with the hardware or if it's from noise.  Wish I had another radio to hook up and see if the noise looks the same.

If any have a few moments I've made a video.  https://youtu.be/8oJ4etAN_iw

[Neil Howard]

Ron , 

    The noise in that video looks to me suspiciously like the dreaded "internet over powerline" (PLC) interference  -  It is horrifically common in England, where HF is really hard to use anywhere near housing these days!

You "not really close" neighbours may have installed  PLC devices to extend their network into a shed or something, which is probably radiating via the powerlines :(  

Those evil beasts turn a house's wiring into broadband radiators. 

Might be worth door knocking if you are friendly and offering to help them with a simple WiFi extender instead :) 

Neil

M0KNC  

[Ron Lewkowicz]

Thank you Neil.  When you experience this noise from PLC  devices does it cause the ADC lights to come on the HL2?    If I turn the LNA gain up the noise mostly goes away and receive seems normal.  I think I had previously mentioned that I thought the S meter was reading high, I don't think this is the case actually.  My issue is that by about -9 LNA gain both the 75 and 100 ADC light are lit full time.  If I ignore those and push the LNA gain up the radio seems to work as it should. 

Closest neighbour is 1/2 mile. I have 5 within a mile radius.  

I need to get some time to take this out portable and away from power lines.

[ron.ni...@gmail.com]

How does your HL2 receiver behave at various gain levels when connected to a dummy load instead of an antenna?  That information might help isolate whether the noise source is internal or external to the HL2.  73, Ron, n6ywu

[Ron Lewkowicz]

On a dummy load I can push LNA gain all the way up to 48 and no ADC lights come on.  If I can attach a photo you'll see what that looks like.....

[Steve Haynal]

Hi Ron,

Checking the RX with a dummy load attached is a good way to test the health of the receiver. Your bandscope screenshot at +48dB looks very similar to what I see with a HL2 here. If you lower the RF LNA to -12 dB, do you see about a ~24dB change in the floor? This would indicate that the RF LNA and ADC are probably operating correctly.

73,

Steve

kf7o

[Ron Lewkowicz]

Hi Steve.  Yes with the dummy load I see around 23dB change from -12 to +48.  It would seem the HL2 is still fine, I'm just dealing with the effects of a massive increase in noise.  This happened very shortly after the power distribution company  were out to install a new auto re-closer on the other side of my home quarter so I suspect that may be the culprit.   

Thanks to everyone for their comments and suggestions.  

[zl2...@gmail.com]

I have been trying to remedy the same problems. I think the problem is in software/ settings as it is happening with one PC and not on others. (same HL2 and antenna.)

I am away from home for a week so keen to get back and start again.

73 ZL2TPQ