Airspy HF+ False Tetra images in the Air Band

[bbrown175]

I recently purchased an Airspy HF+ from Moonraker in the UK. I also own an Airspy R1 which I had always been happy with. I found a strange problem recently with the HF+ when I found what were clearly Tetra images from UHF appearing strongly in the Air Band. I cannot see similar images with the Airspy R1 or an old RTL dongle that I have. I was puzzled by this because I could see that Tetra signals in my area are not particularly strong, so I couldn’t understand why they appeared so strongly at around 130 MHz. See attached image.

I tried to post on the airpsy.group.io to see whether anyone else had seen similar UHF images, but I got a response from the Airspy owner Youssef Touil that the problem would be solved if I added extra filtering. I was sure that this couldn’t be an overload issue, so I applied two signals to the HF+ from two RF signal generators via a power combiner with both signals at -70 dBm. One signal was at 130 MHz and the other was at just over 390 MHz. The 390 MHz signal was clearly present close to the real signal at 130 MHz and the test showed that the spurious image was only 25 dB lower than the 390 MHz signal.

I replied to Mr Touil that when I purchased the product, Airspy had made a big deal about the fact that no additional external filtering would be needed with the HF+, a claim that they have now removed from their website. Given the suppression of UHF Tetra signals in the Air Band is only 25 dB, it is clear that in fact a LOT of extra filtering is required to make this band usable. I asked Mr Touil why he would not allow my post to go on the group – I wanted to understand whether others had seen the same issue or whether I had a bad device and he replied that my post was really a customer support question and they do not allow customer support questions to be posted on the group. I felt that he was very clearly censoring my post as it contained information about the product that he did not like andf did not want widely disseminated.

I am more disappointed about the attitude and lack of transparency than the problem itself, but it is clear that without substantial amounts of UHF filtering, the HF+ is useless for scanning the Air Band 

Bobby

 

[VHFgeraint]

That's bizarre, I was just about to raise a post about the same thing. I also have recently bought an HF+ and was very impressed with the reports of fantastic sensitivity and dynamic range.
I live in remote rural Wales, so VHF signals are pretty weak here, but I also see tetra signals all over the Air Band. I thought I was going bonkers.
So you are saying that I cannot get rid of these without adding a load of extra filtering?

- Geraint

 

[quad_track]

You need to reduce LNA gain, pretty sure the LNA is getting overloaded. The Tetra signals are very strong everywhere, they have to be.
If you either put in a notch filter for the 390 MHz band or drop the LNA gain 10-20 dB the images will go away. Every SDR has this problem, not just the airspy.
Professional hardware has band pass filters for every band they use, but those are expensive.

 

[VHFgeraint]

You can't turn the gain down on the HF+. It has a fully integrated RF AGC system with no possibility of manual override. You are also incorrect about the Tetra signals being strong where I live.
I don't actually think that this problem is due to overload. The spurious signals appear at 1/3 or 1/5 of the frequency that the original signal appears at. To me this seems more like harmonics of the LO mixing the signals in band and if so, turning down the RF gain will not fix the problem. I think the Airspy suggestion made to Bobby, that filtering needs to be added to make these bands useable is almost certainly correct.

Geraint

 

[Flatliner]

VHF air is an unusable mess of TETRA images.
.
.

 

[Flatliner]

bbrown175 Be very careful about what you write in that group. In the past, I too made posts that were never published so I too was censored. Youseff is very protective over this business and my quick calculation suggests that he has made quite a lot of money from us, the SDR Cash Cow Crowd. At best you will be made to look like you are you simply against him, or are just incompetent - or both. At worst, you will be removed (eventually, I was). Even Leif SM5BSZ has had his Youtube video results of images on HF ridiculed, resulting in some back-room "negotiations" requesting that he removes the video, pending a possible future improvement.

I am as well-equipped as Leif and I came to the same conclusion by the end of day 1 of owning two HF+s.

 

[invergordon]

Y....... images will go away. Every SDR has this problem, not just the airspy.
......

And for this reason I have reverted to analogue radios for airband listening. Having had an HF+ I wasn't particularly impressed with its performance on HF or VHF airband so it got sold.

Using SDR for airband is such a time-consuming activity, finding, downloading, configuring software,setting up plugins that scan, digital recorders and setting bandwidths etc. etc.is such a pain. But I see their usefulness in the overall concept of wideband scanning but when it comes down to it my ears are the best tool I have for listening and an analogue radio serves my purpose just fine. Back to enjoying listening and less time fluffing about!!

 

[JELAIR]

And for this reason I have reverted to analogue radios for airband listening. Having had an HF+ I wasn't particularly impressed with its performance on HF or VHF airband so it got sold.

Using SDR for airband is such a time-consuming activity, finding, downloading, configuring software,setting up plugins that scan, digital recorders and setting bandwidths etc. etc.is such a pain. But I see their usefulness in the overall concept of wideband scanning but when it comes down to it my ears are the best tool I have for listening and an analogue radio serves my purpose just fine. Back to enjoying listening and less time fluffing about!!

Which radio would you recommend for airband listening?

I currently use an airspyR2 that scans the entire defined airband somewhere around 10 times a second.
It's fast enough that I get the beginning of all transmissions.

But I would like a dedicated radio for it though. Preferably a portable one if that is possible. But I don't know the market for dedicated radios, so I have zero idea which make or model is worth throwing money at.

Any advice would be nice

PS: I did in fact think about getting the HF+ for the airband, but all the reviews I have read are negative. And I also think it is a bit of a circus they way they keep updating its firmware (Like it was released too early before really being ready. I even read you have to open it and break out your soldering-iron to even be able to update its firmware. Seems weird for such an expensive device. Doesn't give me much confidence in that company)

 

[Voyager]

And I also think it is a bit of a circus they way they keep updating its firmware (Like it was released too early before really being ready.

SDR is a constant evolution of updates by the nature of SDR. If there were no updates, you would probably be complaining about the lack of support.

Are you also complaining about the benefits that came with those updates?

I believe the latest update just released makes the noise figure 8 dB better.

I even read you have to open it and break out your soldering-iron to even be able to update its firmware. Seems weird for such an expensive device. Doesn't give me much confidence in that company)

What you read is completely wrong and I can say that for a fact.

The first version of firmware had a bug in the update routine that required you to jumper two pads using something like a paper clip. Subsequent updates are done using the USB port.

If something seems too weird to be true, it probably isn't true.

On the scanner for Airband, it will be interesting to see what the SDS100 offers.

 

[invergordon]

Which radio would you recommend for airband listening?

I currently use an airspyR2 that scans the entire defined airband somewhere around 10 times a second.
It's fast enough that I get the beginning of all transmissions.

But I would like a dedicated radio for it though. Preferably a portable one if that is possible. But I don't know the market for dedicated radios, so I have zero idea which make or model is worth throwing money at.

Any advice would be nice

PS: I did in fact think about getting the HF+ for the airband, but all the reviews I have read are negative. And I also think it is a bit of a circus they way they keep updating its firmware (Like it was released too early before really being ready. I even read you have to open it and break out your soldering-iron to even be able to update its firmware. Seems weird for such an expensive device. Doesn't give me much confidence in that company)

My personal choice is a Signal R-532. They are long in the tooth but still very sensitive and have a perfect niche in this area. They can be 'portable' in as much as they can be vehicle mounted but not handheld unless you can find a battery pack which are few and far between. For portable I would go for a Yupiteru VT-125 or VT-225 if you require military UHF.

I've owned an R-532 on and off now for 30 years and keep coming back to them after sampling many others.

 

[JELAIR]

SDR is a constant evolution of updates by the nature of SDR. If there were no updates, you would probably be complaining about the lack of support.

Are you also complaining about the benefits that came with those updates?

I believe the latest update just released makes the noise figure 8 dB better.

When an update is needed, it should of course be posted

But a product that has had 14 different firmwares, all within the first 6 months of product release, was simply released too early (In my opinion, of course)

6 of the firmware-updates came in February alone. Some even only ONE day apart! That's just too much and suggests a sloppy company obsessed about speed rather than quality. As if the product was released while still in its beta-stage. That's the impression I'm left with.

It's their choice, of course, but it has at least turned ME off buying it (They probably don't lose sleep over that, and maybe I will come back once the dust has settled and if I haven't bought something else in the meantime. I currently have the AirspyR2 and it is great, it simply works. That, to me, is a good product )

What you read is completely wrong and I can say that for a fact.

The first version of firmware had a bug in the update routine that required you to jumper two pads using something like a paper clip. Subsequent updates are done using the USB port.

Thanks for the update. I noticed it now when reading the page with all their firmware-revisions.
I think it's still a bug that should never have made it past quality-control though.

On the scanner for Airband, it will be interesting to see what the SDS100 offers.

Thank you

My personal choice is a Signal R-532. They are long in the tooth but still very sensitive

Thanks
However, I watched a video about it and noticed it's 25 KHz freq-spacing... which obviously won't be compatible with the new 8.33 KHz channels that have come into effect (At least in theory, until they start to actually allocate them. Some channels will be mapped off of their listed frequency (Not by much, but still), so it will be a non-trivial task to handle them all correctly )

For portable I would go for a Yupiteru VT-125 or VT-225 if you require military UHF.

VT-125 is also 25 KHz freq-spacing.

VT-225 is 10 KHz freq-spacing, minimum... I suppose that might be close enough for most things (If the scanning can handle it)

I fear this new move to 8.33 KHz will leave almost all older scanners with some problems. I don't know how many scanner-models are available yet that come standardized to the new rules.

 

[invergordon]

When an update is needed, it should of course be posted
I fear this new move to 8.33 KHz will leave almost all older scanners with some problems. I don't know how many scanner-models are available yet that come standardized to the new rules.

Aah, fair comment, living and listening in New Zealand isn't an issue as we have no need of 8.33kHz frequency steps, just not enough airspace to warrant it, I had forgotten that the northern hemisphere was moving forward with the implementation of those steps. My apologies and I guess the R-532 and Yupi models will not be much use to you. In that case I'll leave others to provide the guidance.

 

[Voyager]

When an update is needed, it should of course be posted

But a product that has had 14 different firmwares, all within the first 6 months of product release, was simply released too early (In my opinion, of course)

6 of the firmware-updates came in February alone. Some even only ONE day apart! That's just too much and suggests a sloppy company obsessed about speed rather than quality. As if the product was released while still in its beta-stage. That's the impression I'm left with.

It's their choice, of course, but it has at least turned ME off buying it (They probably don't lose sleep over that, and maybe I will come back once the dust has settled and if I haven't bought something else in the meantime. I currently have the AirspyR2 and it is great, it simply works. That, to me, is a good product )

I suspect many of the updates came about as a result of user feedback.

As for "too many updates", I disagree. It's nice to see such vigorous support. Remember "Firmware Friday" when Uniden was public testing the DMR firmware? Lots of users loved that. Some even commented when it was done that they missed it.

I'm sure issues were resolved in each SDR update, and if one of those fixes was for something you had an issue with, you would want to released ASAP.

But, if you really think there are "too many updates", just buy it and ignore the updates. When you get to the point you want to update, do it. There is no requirement to update.