IF DSP vs. crystal filtering

I was just getting ready to buy my first HF rig until I talked to a ham with many years of experience who says not to get any radio with IF DSP. He says that DSP is not as good nor as reliable as physical crystal filters and that if the digital circuitry fails there is no way to bypass the DSP. He says AF DSP is ok because it usually can be switched off.

I've always read that IF DSP was a good and desirable thing to have. Now I'm not so sure ...

What do you guys think?

My opinion is biased because I've never owned an HF radio that didn't have IF DSP.

That said, my opinion is that while a crystal filter may have better specifications at it's design parameters than a DSP filter, the DSP filter beats all comers with regard to operating flexibility. IF DSP gives you the ability to dial up pretty much any IF filter bandwidth or IF shift that you might need. In radios where the IF DSP does the notch filtering, it's typically implemented as an automatic notch filter that finds the squeals and tuner-uppers and kills them in the IF. Some DSP notch filters are also implemented as a manual notch with adjustable width and position. And, if the IF is designed for it, the DSP filtering occurs before the AGC so that the AGC ignores signals that are being blocked by the DSP.

As for reliability of IF DSP, modern HF radios are generally so darn reliable overall that comparisons to HF radios from 20-30 years ago is moot.

jk77 said:

What do you guys think?

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I think he's wrong. IF DSP is vastly superior to DSP done at AF. Digital filters can be made to have very steep skirts and no ringing. There's a reason crystal filters have been made obsolete.

I've had both and IF DSP is far superior. I would never go back to crystal filters.
BB

The 'If the DSP circuit breaks...' sounds like post-choice or maybe anti-upgrade rationalization.
I'll bet this same friend doesn't like CTCSS/PL radios & repeaters because 'unreliable and money.'

Of all the things to fail in a modern radio, the DSP circuit must be nearly last on the list of probables.
The finals, the power supply, the display, the audio amplifier, the ATU (if equipped), mechanical switches buttons/keys, knob rotor encoders, I/O connectors ALL seem much more vulnerable to failure.

I've heard transistors are unreliable and we should stick with tubes.

High performance DSP radios have crystal or other type of hardware filtering before the DSP to improve performance. This is to make sure the A to D converter is not overloaded and run to the rails or out of bits from large out of band signals.

IF DSP in itself does not always mean good or great performance, I've had some IF DSP radios that were grim due to poor implementation of the signal processing. I've had others that performed ok but the actual IF BW was nowhere near what what was selected. Bottom line is the radio mfr has to do a good job on the hardware front end, mixer and the DSP to equal a good or great performing radio.

One example of this is the Tentec Jupiter/Paragon where you could select a 1KHz DSP IF filter for SSB but you still hear high frequency sibilance in the voices, which means its still passing signals at least a few KHz wide. Other radios like the Harris RF-5000 series are like a brick wall where you can have massive interference at the edge of the receiver passband and you select the next narrower IF filter and the interference is completely gone. I also have a Tentec Omni VII which is a very good performing DSP radio, a Tentec Eagle which is a really really good performing DSP radio and both the Elecraft K3 and KX3 which are both top notch in performance.

Another example of not so good DSP is comparing the old Icom IC-706MKIIG to its replacement, the IF IC-7000. The 706 was a good performer, not great but good. The 7000 offered full DSP IF with lots of different BW selections but its ultimate performance falls way below the 706 series in ultimate receiver performance. I know lots of people who supposedly upgraded from a 706 to a 7000 and then wanted their 706's back when they discovered performance went backward. The 7000 problems show up mostly when the radio is on a large antenna and the receiver gets subjected to strong signals and usually not in a mobile setup.

So choose your radio wisely and based some on specs, some on reviews and some on real life experience. You can't go wrong with a radio in the top dozen or so on Rob Sherwood's list since you can't get there without some great performance, but also get a radio that you can live with which includes functions, layout and a sound that suits you.
prcguy

Thanks for the responses. This question came about because I am/was going to get either the Yaesu FT-450D or the Icom IC-7200 (I want to look at them before making my final decision, but I am heavily leaning towards the Yaesu). Anyway, this ham said that I'd be making a mistake and that I should be getting the Kenwood TS-480SAT or the Yaesu FT-857D or even the Icom IC-718 because they all use real crystal filtering and are under a grand (which is my cut-off).

zz0468 said:

There's a reason crystal filters have been made obsolete.

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I don't think I'd say 'obsolete'. If obsolete, they should not sell for anywhere near the price they still get for them.
It's not like they are not out there like an extinct animal or plant, they are out there and often sitting in someone's parts bins but my gosh do they get some serious cash for the good ones!

Yes, some filters are rare as the ones still out there are still being used but I also see commonly desired filters in new unopened boxes (in large quantities) demanding hundreds of dollars each.

As prcguy mentioned, a well designed radio will use both and if done right, it will work wonders.

I think many also have a way of bypassing a failed IF DSP circuit with some as easy as flipping a switch to remove them from the circuit. That was done for functional design much more than it was done in case of failure.

I I have an FT-857 and use it on rare occasion as a battery operated portable rig but would not be happy if it were my only HF rig. Otherwise I have not used any of the other radios you mentioned.

I will say the person steering you away from a radio with DSP IF is not very informed and is giving out bad advise. If you have not visited Rob Sherwood's site here is a link: Receiver Test Data

This will give you an idea of how different receivers might perform in a high level and crowded contest situation. It takes a lot of engineering know how and $$ to rank high on this list but there are other things that should also influence your decision.

I have seen popular radios that some people have raved about like the Yaesu FT-2000, which was fairly expensive but it ranks near the bottom of the list and even though it looks cool and has lots of knobs and such, it would not do well on a big antenna on a crowded band. I suspect a Yaesu FT-817 would have better selectivity and dynamic range over an FT-2000.

I think its good to choose some radios within your price range, narrow them down to features you like and maybe size and battery consumption if portable ops is your thing, then use the Sherwood list to see if there are any big performance gaps.

prcguy

jk77 said:

Thanks for the responses. This question came about because I am/was going to get either the Yaesu FT-450D or the Icom IC-7200 (I want to look at them before making my final decision, but I am heavily leaning towards the Yaesu). Anyway, this ham said that I'd be making a mistake and that I should be getting the Kenwood TS-480SAT or the Yaesu FT-857D or even the Icom IC-718 because they all use real crystal filtering and are under a grand (which is my cut-off).

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jk77 said:

This question came about because I am/was going to get either the Yaesu FT-450D or the Icom IC-7200.

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I think either of these are probably good choices. If you have any interest in the sound card digital modes, the IC-7200 has a built-in USB sound card which makes interfacing the radio to your computer a breeze.

jk77 said:

Anyway, this ham said that I'd be making a mistake and that I should be getting the Kenwood TS-480SAT or the Yaesu FT-857D or even the Icom IC-718.

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The TS-480SAT is a good radio, but an older design compared to the FT-450D or IC-7200. One advantage it has is that you can separate the control head from the RF deck. That might help with mounting the radio...or it may be no advantage at all. The FT-857D is a mobile radio and I think the ergonomics may not be good when used as a base rig. The IC-718 is a very basic HF radio--I've used one and the feature set is limited compared to your other choices.

Hams made contacts for decades before there was any kind of DSP. The concept that you have to have it ignores all that history and experience. Crystal filters are essential whether you have IF DSP or not. Stop obsessing over this stuff. Get a radio and get on the air.

W9BU said:

I think either of these are probably good choices. If you have any interest in the sound card digital modes, the IC-7200 has a built-in USB sound card which makes interfacing the radio to your computer a breeze.

The TS-480SAT is a good radio, but an older design compared to the FT-450D or IC-7200. One advantage it has is that you can separate the control head from the RF deck. That might help with mounting the radio...or it may be no advantage at all. The FT-857D is a mobile radio and I think the ergonomics may not be good when used as a base rig. The IC-718 is a very basic HF radio--I've used one and the feature set is limited compared to your other choices.

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My votes would be for the IC-7200 and the FT-857D; the former for its built in sound and radio control (one USB cable) and the latter for its internal DSP (not sure if it's simply an AF one or IF). If getting the latter, the remote mounting kit is a nice way to keep a clean desktop and you can always get the control cable and use software to control it.

Yes, yes and yes. But there are lots of new features and performance to be had in new radios and if you have a fixed budget its nice to kick all the tires before shelling out the $$. For me personally, DSP based radios have enhanced my enjoyment of the hobby and in the next week I'm thinking of adding a Flex Radio to my collection of junk.
prcguy

ko6jw_2 said:

Hams made contacts for decades before there was any kind of DSP. The concept that you have to have it ignores all that history and experience. Crystal filters are essential whether you have IF DSP or not. Stop obsessing over this stuff. Get a radio and get on the air.

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The FT-857 DSP is simply an audio equalizer and it doesn't have variable IF BW and other features offered in later designs.
prcguy

N8OHU said:

My votes would be for the IC-7200 and the FT-857D; the former for its built in sound and radio control (one USB cable) and the latter for its internal DSP (not sure if it's simply an AF one or IF). If getting the latter, the remote mounting kit is a nice way to keep a clean desktop and you can always get the control cable and use software to control it.

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I had an IC-718 and then made the leap to an IC-756 1st generation "classic" (non-PRO). I saved my nickels and dimes and eventually upgraded to an IC-756Pro with DSP... and I never looked back!

I say go with the Icom... but then again, I am biased!

The reason I'm obsessed with getting it right is because I'm on a budget and cannot afford to make a costly mistake. The radio will probably be with me for quite some time into the future.

One other comment this ham made was that the signal processed by the DSP was not the true analog signal but a sampled one and that information is lost in the sampling process kind of like mp3s don't sound as good as the old analog recordings.

I don't know ... I respect this guy because he has many years of experience and generally knows what he is talking about. He is just very anti-DSP. But I get where he is coming from. Adding in a digital layer is just distancing the operator from the real signal.

I want to point out that I'm not interested in contesting. I'm interested in the physics of radio propagation basically studied by casual dxing. So I want to be as close to the actual signal as possible. That's why what he said has given me pause.

Anyway, thanks guys for your responses. They do make a lot of sense and I just am going to have to think about it some more.

73s

I understand you desire to get it right, but in my opinion your very anti-DSP friend is not helping. Its communication bandwidth audio and if you are talking with a ham you have talked with in person you should be able to recognize his voice. If not it will not be the DSP, but more about how the radio is adjusted by RF frequency, IF bandwidth or shift, Noise Reduction and other variables you have no control over.

DSP can help you hear and understand what is being said. Its not going to be studio quality audio as I said earlier, its "communication bandwidth audio". If you can hear it and don't understand what is being said, you can't work it. DSP can help. Will you hear it like he/she is sitting next to you. That's not likely, DSP or not.

jk77 said:

The reason I'm obsessed with getting it right is because I'm on a budget and cannot afford to make a costly mistake. The radio will probably be with me for quite some time into the future.

One other comment this ham made was that the signal processed by the DSP was not the true analog signal but a sampled one and that information is lost in the sampling process kind of like mp3s don't sound as good as the old analog recordings.

I don't know ... I respect this guy because he has many years of experience and generally knows what he is talking about. He is just very anti-DSP. But I get where he is coming from. Adding in a digital layer is just distancing the operator from the real signal.

I want to point out that I'm not interested in contesting. I'm interested in the physics of radio propagation basically studied by casual dxing. So I want to be as close to the actual signal as possible. That's why what he said has given me pause.

Anyway, thanks guys for your responses. They do make a lot of sense and I just am going to have to think about it some more.

73s

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Thank you, mcscanner. That does clarify a lot for me. Yes, my number one concern should be intelligibility.

I would go with the 7200, which I have and can speak from experience. ICOM has an excellent implementation of DSP filtering, noise reduction and noise blanking. Not all DSP circuits are created equal! ICOMs twin band pass tuning is also very good. See the reviews of the IC-7200 on eHam.net. I also have Yaesu gear. ICOMs DSP NR, NB and filtering do a very good job without causing excessive distortion to audio quality, which unfortunately is an issue with some trancievers like Kenwood's 570 and 590 series rigs - they sound "watery" with DSP engaged. Yaesu has done well with DSP too, but their audio tends to be a little more bassy. ICOM has more of a "communications" quality sound. It's all what you prefer.
If you have a retailer near you, I would recommend sitting down with a few rigs to experience what they sound like, how they look and how you "work" the trancievers. We all have different preferences and interests with features.
Good luck and enoy!
BG..