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moderated Help me understand how SDR front-ends work


Richard
 

I have been using an Airspy HF + Discovery for two months. I use it with SDR+.

I was impressed with the noise reduction and selectivity.

The past 10 days I suddenly get distorted MW stations every 10 khz through the HF bands. 5000 - 6700 is the worst but they are everywhere.

I have a 200 foot random wire outside as an antenna. I also have a You Loop inside. The MW signals aren't present with the YouLoop. I also have a Drake R8. This problem doesn't occur with that either.

I realize 200 feet is alot but I had no problem for two months. Is it possible my SDR is damaged now?

The is an HF Preamp that was set to on by default. I left it that way. There is also HF AGC. When I turn that off it opens an attenuation slider. If I turn off Preamp, HF AGC and add 30 db attenuation the signals are lowered but the MW signals are just as present.

I bought an MW filter and placed before the Airspy and the problem is gone now with the except of getting a harmonic of a local AM station at 3330. That wasn't there before.

Nothing has changed with my outside wire. I can't see it's making contact with anything new. I don't seem to be getting HG stations as well now but not sure if it's just propogation problems.

Could I have damaged my Airspy?

Thanks!


prog
 

On Fri, Feb 19, 2021 at 06:37 PM, Richard wrote:
Could I have damaged my Airspy?
Check whatever you are feeding to the unit for harmonics etc.


Kriss Kliegle
 

Check UR email, private message sent!

73 Kriss KA1GJU


jdow
 

Corroded antenna connection?

{^_^}

On 20210219 08:32:18, Richard wrote:

I have been using an Airspy HF + Discovery for two months. I use it with SDR+.

I was impressed with the noise reduction and selectivity.

The past 10 days I suddenly get distorted MW stations every 10 khz through the HF bands. 5000 - 6700 is the worst but they are everywhere.

I have a 200 foot random wire outside as an antenna. I also have a You Loop inside. The MW signals aren't present with the YouLoop. I also have a Drake R8. This problem doesn't occur with that either.

I realize 200 feet is alot but I had no problem for two months. Is it possible my SDR is damaged now?

The is an HF Preamp that was set to on by default. I left it that way. There is also HF AGC. When I turn that off it opens an attenuation slider. If I turn off Preamp, HF AGC and add 30 db attenuation the signals are lowered but the MW signals are just as present.

I bought an MW filter and placed before the Airspy and the problem is gone now with the except of getting a harmonic of a local AM station at 3330. That wasn't there before.

Nothing has changed with my outside wire. I can't see it's making contact with anything new. I don't seem to be getting HG stations as well now but not sure if it's just propogation problems.

Could I have damaged my Airspy?

Thanks!



John Barnett
 

You say you don't get any MW signals with the Youloop! I checked mine this morning 09.38 UK time and signals are booming in. My Youloop is in the loft in a temporary position

John UK..


On 20 February 2021 00:20:08 (+00:00), jdow wrote:

Corroded antenna connection?

{^_^}

On 20210219 08:32:18, Richard wrote:

I have been using an Airspy HF + Discovery for two months. I use it with SDR+.

I was impressed with the noise reduction and selectivity.

The past 10 days I suddenly get distorted MW stations every 10 khz through the HF bands. 5000 - 6700 is the worst but they are everywhere.

I have a 200 foot random wire outside as an antenna. I also have a You Loop inside. The MW signals aren't present with the YouLoop. I also have a Drake R8. This problem doesn't occur with that either.

I realize 200 feet is alot but I had no problem for two months. Is it possible my SDR is damaged now?

The is an HF Preamp that was set to on by default. I left it that way. There is also HF AGC. When I turn that off it opens an attenuation slider. If I turn off Preamp, HF AGC and add 30 db attenuation the signals are lowered but the MW signals are just as present.

I bought an MW filter and placed before the Airspy and the problem is gone now with the except of getting a harmonic of a local AM station at 3330. That wasn't there before.

Nothing has changed with my outside wire. I can't see it's making contact with anything new. I don't seem to be getting HG stations as well now but not sure if it's just propogation problems.

Could I have damaged my Airspy?

Thanks!



-- 
Sent with the new, awesome Vivaldi mail client / browser. Download it at vivaldi.com.


jdow
 

I read it that he did not hear harmonics on the YouLoop but did with his 200' long wire. If the receiver settings are really the same between the two then likely the long wire has a corroded connection. The other possibility is running on MW or HF with the Discovery set to manual gain control with preamp on and zero attenuation - or some variation similar to that. (If he is doing that he should probably spank himself unless he understands what he is doing.)

{^_^}

On 20210220 01:39:56, John Barnett wrote:
You say you don't get any MW signals with the Youloop! I checked mine this morning 09.38 UK time and signals are booming in. My Youloop is in the loft in a temporary position

John UK..

On 20 February 2021 00:20:08 (+00:00), jdow wrote:

Corroded antenna connection?

{^_^}

On 20210219 08:32:18, Richard wrote:

I have been using an Airspy HF + Discovery for two months. I use it with SDR+.

I was impressed with the noise reduction and selectivity.

The past 10 days I suddenly get distorted MW stations every 10 khz through the HF bands. 5000 - 6700 is the worst but they are everywhere.

I have a 200 foot random wire outside as an antenna. I also have a You Loop inside. The MW signals aren't present with the YouLoop. I also have a Drake R8. This problem doesn't occur with that either.

I realize 200 feet is alot but I had no problem for two months. Is it possible my SDR is damaged now?

The is an HF Preamp that was set to on by default. I left it that way. There is also HF AGC. When I turn that off it opens an attenuation slider. If I turn off Preamp, HF AGC and add 30 db attenuation the signals are lowered but the MW signals are just as present.

I bought an MW filter and placed before the Airspy and the problem is gone now with the except of getting a harmonic of a local AM station at 3330. That wasn't there before.

Nothing has changed with my outside wire. I can't see it's making contact with anything new. I don't seem to be getting HG stations as well now but not sure if it's just propogation problems.

Could I have damaged my Airspy?

Thanks!



-- 
Sent with the new, awesome Vivaldi mail client / browser. Download it at vivaldi.com.


Richard
 

Thanks. The outside connection is only a few weeks old but I can check that.


Richard
 

I didn't get MW signals in the HF bands with the Youloop. It did pretty good at tuning MW stations where they were supposed to be.


Richard
 

I probably don't know what I'm doing.

What I was hearing I don't think was harmonics because I heard the same thing every 10 khz.After I installed the MW filter the ghost signals went away but I did pick up a harmonic at 3330 Khz that wasn't there before.

The preamp was on by default and I left it on. It was not a problem for two months.

I have been uncertain how to set things. I have HF AGC, HF Preamp, and HF Threshold. If I turn off HF AGC I get an attenuation slider. I wasn't having signs of overload before. Can running with too much gain damage the Airspy?

As mentioned in original post before adding the MW filter  I did turn off preamp and HF Gain and set 30db attenuation and the ghost signals were still there just quieter.

The one thing I didn't mention was that out of 10 days where this was a problem I had two days where there weren't MW signals in the HF. Maybe more evidence it is a bad connection. I had not thought of that causing something like this. I will check when weather better.

Thanks for replys.


Ken Sejkora
 

Hi Richard,

 

How do you ‘transfer’ the signals from the longwire antenna to the SDR?  Is the antenna connected to a coax cable which runs to the house, and then to the SDR?  Or is the antenna connected directly to a dropwire that runs into the house and connects to the center pin of the SDR antenna connector?

 

I think jdow may be on to something with her suggestion about a corroded connection.  Any corrosion on any of the transitions from antenna->coax->SDR or antenna->dropwire->SDR introduces the possibility of creating a “diode detector” in the circuit.  The corrosion can sometimes act like a semiconductor, which can act as an RF detector, and cause havoc.  In the “old days” of crystal radio, the “detector” was often a “catwhisker” wire touching a piece of galena (lead sulfide) or carborundum or other such material.  In the case of the galena, you didn’t want the “catwhisker” wire to make a direct connection to the conductive galena, but rather to just barely touch the oxide layer on the surface of the galena crystal.  That thin oxide layer between the catwhisker wire and the galena crystal acted as a semiconductor diode.  In later versions of “crystal” radios, the catwhisker+galena was replaced with a true semiconductor, such as a germanium 1N34 diode.

 

Anyway, if you have a corroded connection, such as wires just twisted together, corrosion can build up and act as a detector.  If you have a strong AM signal nearby, that detected RF can “bleed” into the RF path and cause spurious signals, intermodulation, etc.  The best solution to prevent this is to thoroughly clean both wires to bare, shiny metal, twist them together, and then solder the connection.  The solder will ‘bond’ the wires together and prevent ingress of corrosion.  As a final step, it is best to heat-shrink or at least tape the junction with electrical tape.

 

As I mentioned in an earlier reply to you, connecting the longwire antenna directly to the SDR, either via a coax or dropwire, is asking for trouble.  Static charges of several hundreds or even thousands of volts can build up on the longwire and fry the front end of an SDR.  A much better configuration is to solder a dropwire to the elevatedlongwire antenna, and then connect the dropwire into one branch of the primary of a 9:1 unun transformer, and the other end of the primary to a good ground.  This will drain off any static on the antenna into the ground.  The secondary of the unun transformer would be hooked to a coax line running to your SDR.  This will provide a better match of the longwire to the radio, and will likely increase signal levels, as well as reducing some of the noise.  However, this configuration will NOT prevent the coax from picking up noise inside your house and re-radiating it into your antenna system.  Other measures, such as common-mode-chokes can help here.

 

As jdow suggested, disassemble, inspect, and clean ANY connections in the antenna-to-SDR pathway.  Use an unun transformer to match the impedance and drain off static charges. Some suppliers such as Nooelec call the matching transformer a “balun” (balanced-to-unbalanced), but it technically is an unun (unbalanced-to-unbalanced).  To reduce local noise on the coax cable, use common-mode chokes, ideally one at the end of the coax connecting to the unun near the antenna, and another one at the end of the coax feeding into the SDR.

 

I hope these considerations help.  Good luck, Richard.

 

Ken, WBØOCV

 

From: Richard
Sent: Sunday, February 21, 2021 04:10 PM
To: airspy@groups.io
Subject: Re: [airspy] Help me understand how SDR front-ends work

 

I probably don't know what I'm doing.

What I was hearing I don't think was harmonics because I heard the same thing every 10 khz.After I installed the MW filter the ghost signals went away but I did pick up a harmonic at 3330 Khz that wasn't there before.

The preamp was on by default and I left it on. It was not a problem for two months.

I have been uncertain how to set things. I have HF AGC, HF Preamp, and HF Threshold. If I turn off HF AGC I get an attenuation slider. I wasn't having signs of overload before. Can running with too much gain damage the Airspy?

As mentioned in original post before adding the MW filter  I did turn off preamp and HF Gain and set 30db attenuation and the ghost signals were still there just quieter.

The one thing I didn't mention was that out of 10 days where this was a problem I had two days where there weren't MW signals in the HF. Maybe more evidence it is a bad connection. I had not thought of that causing something like this. I will check when weather better.

Thanks for replys.

 


--

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


Richard
 

Ken
Thanks for the reply.
I did SWL through most of the 90s with a Drake R8 then gave it up. I decided to get back into it last December.
I'm new to SDR and don't understand alot about it. I was into listening for several years but never really learned the techincal end. The Airspy was a surpise in that it didn't pick up much of the electrical interfernce that I think was the reason I got out of the hobby.

The wire ends at a tree outside the house. There is a solder connection to another wire that enters the house. That wire goes to a banana plug into Alpha Delta Antenna switch that I had back in the 90s. There is coax to the SDR with a two adapters to get it into the smc connecter.
I checked the connections for tightness. The coax and addapters except the SMC are old.
Nothing is grounded. No transformers. I don't have a way to get Coax in the house without an upset spouse.
The wire was errected and the solder connection made two months ago. It was cold and the iron wasn't working well and I know I didn't get a great solder job. I taped it and left it.
I'll have to wait till snow melts to check or redo it.

I did buy a 9:1 Balun. I ran a wire down to water pipe in the basement. It didn't make any difference in what I heard or signal level so I disconnected. I'm not sure if my water pipes are a good ground. I don't have a ground source near the radio. I have an old house with ungrounded outlets.

When the weather is better I had planned to come up with a better arrangement. I was trying to get by for now.

As far as damage to the SDR I am still picking up signals. Is it possible to do a little damage or is it just fried or not fried?

Thanks for your reply, I appreciate it.


jdow
 

If it still picks up signals it's probably OK and not half fried unless it seems very numb. I dig about the old house and two wire home wiring. This place is about 120 years old, made of rocks with gaps filled with lime mortar. I stuck a ground rod in outside the place antenna wires come in. (I am NOT in a lightning area by any means. So I used the hole somebody laboriously created for the gas feed into the house.) It is sub-optimal but works.

If you have nearby broadcast stations they can overload the AirSpy. It isn't easy. The HF+ series AirSpys are the exception to my general rule, keep the front end AGC off. Is it possible you turned them off from their default state of on? Hopefully you don't live surrounded by high level stations. On the other hand, you need a big antenna like that for transmitting as efficiency matters. For HF and MW reception the basic rule goes, "If you can connect the antenna and the noise level in the receiver goes up Bob's your uncle - you do not need more antenna or gain." Loops and the like can be used to null noise as well. In some situations this can be very dramatic.

Note that short grounds matter. Long grounds are antennas. Short grounds are less efficient antennas. {^_-}

Small diameter coax exists and for reception only are very useful. Big loops and coils of large coax are indeed ugly. Thin wires can be kept behind furniture and trimmed to length. Negotiate about the "ugly" factor. In one house I made a hole near the baseboard and put an aluminum panel over it for mounting the connectors. I grounded the panel. And it was not generally visible unless somebody looked for it. I worked to keep it neat.

{^_^}

On 20210221 18:31:41, Richard wrote:
Ken
Thanks for the reply.
I did SWL through most of the 90s with a Drake R8 then gave it up. I decided to get back into it last December.
I'm new to SDR and don't understand alot about it. I was into listening for several years but never really learned the techincal end. The Airspy was a surpise in that it didn't pick up much of the electrical interfernce that I think was the reason I got out of the hobby.

The wire ends at a tree outside the house. There is a solder connection to another wire that enters the house. That wire goes to a banana plug into Alpha Delta Antenna switch that I had back in the 90s. There is coax to the SDR with a two adapters to get it into the smc connecter.
I checked the connections for tightness. The coax and addapters except the SMC are old.
Nothing is grounded. No transformers. I don't have a way to get Coax in the house without an upset spouse.
The wire was errected and the solder connection made two months ago. It was cold and the iron wasn't working well and I know I didn't get a great solder job. I taped it and left it.
I'll have to wait till snow melts to check or redo it.

I did buy a 9:1 Balun. I ran a wire down to water pipe in the basement. It didn't make any difference in what I heard or signal level so I disconnected. I'm not sure if my water pipes are a good ground. I don't have a ground source near the radio. I have an old house with ungrounded outlets.

When the weather is better I had planned to come up with a better arrangement. I was trying to get by for now.

As far as damage to the SDR I am still picking up signals. Is it possible to do a little damage or is it just fried or not fried?

Thanks for your reply, I appreciate it.


Richard
 

Thanks for the reply.

I am surrounded by strong MW stations, all up and down the dial.

I purchased an antenna that requires a ground and when the weather gets better I plan on trying to drive a ground rod close to the antenna.

You mention keeping AGC off. There is HF AGC under SOURCE. There is also the separate AGC. I had left them both on. Should they both be turned off?
In the past when I turned AGC off the fading became terrible. Just now I turned it off and got much stronger sounding audio. Maybe I'm confused and was thinking of my old Drake.

Thanks again
Ric


prog
 

On Tue, Feb 23, 2021 at 09:20 PM, Richard wrote:

Thanks for the reply.

I am surrounded by strong MW stations, all up and down the dial.

I purchased an antenna that requires a ground and when the weather gets better I plan on trying to drive a ground rod close to the antenna.

You mention keeping AGC off. There is HF AGC under SOURCE. There is also the separate AGC. I had left them both on. Should they both be turned off?
In the past when I turned AGC off the fading became terrible. Just now I turned it off and got much stronger sounding audio. Maybe I'm confused and was thinking of my old Drake.

Thanks again
Ric

There are many AGCs at different levels:

Analog:

  • RF AGC, which activates a 6dB stepped attenuator,
  • Analog IF AGC, which controls the IF gain just before the digitization.

Digital:

  • Digital IF AGC, to make sure the data is scaled properly (by digital amplification) before sending to the computer,
  • Narrow band AGC, which is the AGC panel controlling the signal that passes through the VFO filter.

Important Notes:

  • The role of the Analog AGCs is to adapt the sensitivity of the front-end to the signals at the input. When enabling the AGC in the Source panel, you are activating both Analog AGCs.
  • The Digital IF AGC is always activated and only starts acting when the strongest signal(s) in the IF spectrum exceed -6 dBFS. This mechanism ensures your signals are always scaled properly for unattended operations.
  • When turning the Analog AGCs off, you can control the stepped attenuator manually, but then, it’s up to you to determine which attenuation level is adequate for your signal at input. In general, push the attenuation until the noise floor is around -100 dBFS. Higher levels do not necessarily improve your SNR but will definitely reduce your available dynamic range. If in doubt, turn the AGC on and let it do the job.
  • When turning the Analog AGC on, you will notice that you also have a “Threshold” option available. It is used to instruct the AGC to tolerate an extra 3 dB of signal power before setting the next attenuation level. “Threshold Low” means the front-end is “less sensitive”, and “Threshold High” means “more sensitive”. This is really useful when chasing marginal signals in presence of very strong blockers (~ 100 dB of difference).
  • The preamp option, might be misleading, and should be probably renamed “postamp.” It has the same effect on the noise figure and the linearity as a preamp, but acts on the back-end (ADC + Digital post processing) of the receiver instead. Basically, turn the “preamp” option off to get an extra 12 dB of dynamic range by scrapping the quantization noise margin.
I hope this helps!


jdow
 

Front end AGC support on:
    AirSpy HF+ and AIrSpy HF+ Discovery
Front end AGC support off:
    Almost all other dongles.

If you are doing MW work - a 10' length of almost any sort of wire will do pretty good. That is to say when hooking the wire to a Discovery the noise level goes up. If that is the case then the only improvement you can get from another antenna would come from being able to use directivity to null noise.

{^_^}

On 20210223 12:20:23, Richard wrote:

Thanks for the reply.

I am surrounded by strong MW stations, all up and down the dial.

I purchased an antenna that requires a ground and when the weather gets better I plan on trying to drive a ground rod close to the antenna.

You mention keeping AGC off. There is HF AGC under SOURCE. There is also the separate AGC. I had left them both on. Should they both be turned off?
In the past when I turned AGC off the fading became terrible. Just now I turned it off and got much stronger sounding audio. Maybe I'm confused and was thinking of my old Drake.

Thanks again
Ric



Richard
 

The bad connection idea appears more likely now.

In addition to the ghost MW signals it seemed like I wasn't picking up HF as well as before. I had bought an MW filter to take care of the MW interference and that worked.
Two days ago I noticed I was getting great HF signals again. I removed the MW filter and there were no spurious signals. It's been that way for 48 hours.

The one factor I didn't mention was that the MW problem started during a period of sub zero temps. It stopped when we got up to 49.
There is one solder connection outside that I made a couple months ago. It was below freezing and my iron wasn't working well. I knew I did a lousy job but it was cold and I taped it and went with it. It makes sense that something changed with the cold weather.

When the snow melts I will have to redo it.

Thanks to all for reply's and patience.


jdow
 

It may be there is a serious dose of design irony here. Ferrite cores can overload and produce IMD. If the cores were ill chosen and not fully tested by the designer it may be that the inductors in your filter are making it useless.

{o.o}

On 20210225 06:52:52, Richard wrote:

The bad connection idea appears more likely now.

In addition to the ghost MW signals it seemed like I wasn't picking up HF as well as before. I had bought an MW filter to take care of the MW interference and that worked.
Two days ago I noticed I was getting great HF signals again. I removed the MW filter and there were no spurious signals. It's been that way for 48 hours.

The one factor I didn't mention was that the MW problem started during a period of sub zero temps. It stopped when we got up to 49.
There is one solder connection outside that I made a couple months ago. It was below freezing and my iron wasn't working well. I knew I did a lousy job but it was cold and I taped it and went with it. It makes sense that something changed with the cold weather.

When the snow melts I will have to redo it.

Thanks to all for reply's and patience.



Richard
 

Update

I had added an MW filter in front of the Airspy HF + Discovery which got rid of the ghost MW signals. I still wasn't geting HF quite as good as I had for two months before. I still have my old Drake R8 and would switch the antenna between the two. They were previously about the same. Now the Drake was better.
One day I suddenly got better HF on the Discovery. I removed the MW filter and no ghost signals. I enjoyed about 10 days of listening like I used to. I made adjustments to AGC and Preamp as suggested by other posters. More on that below.

A couple days ago I suddenly got the MW ghost signals again. Like before every 10 Khz I would hear multiple MW stations distorted. The same stations at every point. After switching back and forth to another antenna this stopped. Since it was a nice day and the snow had melted I decided to redo the one solder connection outside. On inspecting it I saw it really wasn't that bad but I redid it with a good solder job.
I went inside to listen. I got no interference. I have my antennas connected to an old Alpha Delta switch so I can switch different antennas. The switch itself is very stiff and requires effort to turn. While I was starting to switch from my outside wire to a shorter attic wire the ghost signals popped up on the spectrum display. The audio was the same multiple signals. I had not fully switched to the other antenna, still on the outside wire. I quickly moved the outside wire from the switch and attached directly to the Discovery to see if the switch was the problem. Got the same interference.
I had been in the 15 Mhz band. The problem originally was worse in lower bands so  I then tuned to 3 Mhz. I have attached a screen print.

When I started using the discovery I left default settings on - HF AGC, HF Preamp, and AGC. The past two weeks after reading other people's posts I turned off Preamp and experimented with the two AGC settings.
What I found was that the HF-AGC made no difference. If I switched it on or off the audio would drop out a second but would return to what it was. With it off I then had an ATT slider. I found that some stations were better with 6 db ATT some with 0.
The other AGC panel I turned on or off depending on what sounded best but it made no sense. Sometimes I would have it on and tune a strong HF signal with little fading and would hear either nothing or a faint audio. Turning it off would restore a normal volume level. Other times it was the opposite, I would have it off and hear little until I turned it on. Seems odd.

During the time I mention above where I did the screen print I tried setting the ATT to 24db. The interference signals were still there and still heard. I usually have tried to keep the noise floor at 100. You can see it is 90 here even with attenuation. Over the past two days I have had times where the noise floor was 80 or 90 no matter what I set it as and then a little later it is the normal 100. I've also seen fluctuations towards the edge of the spectrum display where it is 120 or 110 then moves up as it gets towards the center of display.
This all seem erratic to me. It seems like the AGC might not working right and maybe something else. I think what may have happened when I triggered a return of the interference by using the switch is that I had it turned enough to cut out the signal and then the AGC went haywire.
But I don't know. This Discovery is a lot more complicated than my Drake.
Does this behavior seem logical?
Does it sound like my Discovery is defective?

Sorry this is  so long. Any input appreciated.

Ric


Al Scanandoah
 

Have you tried connecting the antenna directly to the HF+?


On Fri, Mar 5, 2021, 10:51 Richard <healingconnection@...> wrote:
Update

I had added an MW filter in front of the Airspy HF + Discovery which got rid of the ghost MW signals. I still wasn't geting HF quite as good as I had for two months before. I still have my old Drake R8 and would switch the antenna between the two. They were previously about the same. Now the Drake was better.
One day I suddenly got better HF on the Discovery. I removed the MW filter and no ghost signals. I enjoyed about 10 days of listening like I used to. I made adjustments to AGC and Preamp as suggested by other posters. More on that below.

A couple days ago I suddenly got the MW ghost signals again. Like before every 10 Khz I would hear multiple MW stations distorted. The same stations at every point. After switching back and forth to another antenna this stopped. Since it was a nice day and the snow had melted I decided to redo the one solder connection outside. On inspecting it I saw it really wasn't that bad but I redid it with a good solder job.
I went inside to listen. I got no interference. I have my antennas connected to an old Alpha Delta switch so I can switch different antennas. The switch itself is very stiff and requires effort to turn. While I was starting to switch from my outside wire to a shorter attic wire the ghost signals popped up on the spectrum display. The audio was the same multiple signals. I had not fully switched to the other antenna, still on the outside wire. I quickly moved the outside wire from the switch and attached directly to the Discovery to see if the switch was the problem. Got the same interference.
I had been in the 15 Mhz band. The problem originally was worse in lower bands so  I then tuned to 3 Mhz. I have attached a screen print.

When I started using the discovery I left default settings on - HF AGC, HF Preamp, and AGC. The past two weeks after reading other people's posts I turned off Preamp and experimented with the two AGC settings.
What I found was that the HF-AGC made no difference. If I switched it on or off the audio would drop out a second but would return to what it was. With it off I then had an ATT slider. I found that some stations were better with 6 db ATT some with 0.
The other AGC panel I turned on or off depending on what sounded best but it made no sense. Sometimes I would have it on and tune a strong HF signal with little fading and would hear either nothing or a faint audio. Turning it off would restore a normal volume level. Other times it was the opposite, I would have it off and hear little until I turned it on. Seems odd.

During the time I mention above where I did the screen print I tried setting the ATT to 24db. The interference signals were still there and still heard. I usually have tried to keep the noise floor at 100. You can see it is 90 here even with attenuation. Over the past two days I have had times where the noise floor was 80 or 90 no matter what I set it as and then a little later it is the normal 100. I've also seen fluctuations towards the edge of the spectrum display where it is 120 or 110 then moves up as it gets towards the center of display.
This all seem erratic to me. It seems like the AGC might not working right and maybe something else. I think what may have happened when I triggered a return of the interference by using the switch is that I had it turned enough to cut out the signal and then the AGC went haywire.
But I don't know. This Discovery is a lot more complicated than my Drake.
Does this behavior seem logical?
Does it sound like my Discovery is defective?

Sorry this is  so long. Any input appreciated.

Ric


jdow
 

You never said what happened when you switched to the smaller attic antenna. If you had a change of weather the outside antenna may be defective. That may mean insulation rubbed off, bad (choke puke) wire nut, bad (water inside) feed line. Or it may run close to some other bolted together or strung together object such as a wire fence, aluminum siding on a building, and so forth. If the attic antenna is 10' long or longer and does not have the interference then dollars to donuts your long wire or its environment is a problem. Heck, it could have been a very nearby MW broadcast station knocked off the air by storms and had its power restored coincident with your interference.

All that aside, clean your bloody antenna switch. Its contacts are corroded.

{^_^}

On 20210305 07:51:39, Richard wrote:
Update

I had added an MW filter in front of the Airspy HF + Discovery which got rid of the ghost MW signals. I still wasn't geting HF quite as good as I had for two months before. I still have my old Drake R8 and would switch the antenna between the two. They were previously about the same. Now the Drake was better.
One day I suddenly got better HF on the Discovery. I removed the MW filter and no ghost signals. I enjoyed about 10 days of listening like I used to. I made adjustments to AGC and Preamp as suggested by other posters. More on that below.

A couple days ago I suddenly got the MW ghost signals again. Like before every 10 Khz I would hear multiple MW stations distorted. The same stations at every point. After switching back and forth to another antenna this stopped. Since it was a nice day and the snow had melted I decided to redo the one solder connection outside. On inspecting it I saw it really wasn't that bad but I redid it with a good solder job.
I went inside to listen. I got no interference. I have my antennas connected to an old Alpha Delta switch so I can switch different antennas. The switch itself is very stiff and requires effort to turn. While I was starting to switch from my outside wire to a shorter attic wire the ghost signals popped up on the spectrum display. The audio was the same multiple signals. I had not fully switched to the other antenna, still on the outside wire. I quickly moved the outside wire from the switch and attached directly to the Discovery to see if the switch was the problem. Got the same interference.
I had been in the 15 Mhz band. The problem originally was worse in lower bands so  I then tuned to 3 Mhz. I have attached a screen print.

When I started using the discovery I left default settings on - HF AGC, HF Preamp, and AGC. The past two weeks after reading other people's posts I turned off Preamp and experimented with the two AGC settings.
What I found was that the HF-AGC made no difference. If I switched it on or off the audio would drop out a second but would return to what it was. With it off I then had an ATT slider. I found that some stations were better with 6 db ATT some with 0.
The other AGC panel I turned on or off depending on what sounded best but it made no sense. Sometimes I would have it on and tune a strong HF signal with little fading and would hear either nothing or a faint audio. Turning it off would restore a normal volume level. Other times it was the opposite, I would have it off and hear little until I turned it on. Seems odd.

During the time I mention above where I did the screen print I tried setting the ATT to 24db. The interference signals were still there and still heard. I usually have tried to keep the noise floor at 100. You can see it is 90 here even with attenuation. Over the past two days I have had times where the noise floor was 80 or 90 no matter what I set it as and then a little later it is the normal 100. I've also seen fluctuations towards the edge of the spectrum display where it is 120 or 110 then moves up as it gets towards the center of display.
This all seem erratic to me. It seems like the AGC might not working right and maybe something else. I think what may have happened when I triggered a return of the interference by using the switch is that I had it turned enough to cut out the signal and then the AGC went haywire.
But I don't know. This Discovery is a lot more complicated than my Drake.
Does this behavior seem logical?
Does it sound like my Discovery is defective?

Sorry this is  so long. Any input appreciated.

Ric
Screenshot 2021-03-02 14.11.46.png