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opinion on sdr radios

Discussion in 'Ham Radio Discussions' started by VA6AW, Jan 22, 2013.

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  1. VA6AW

    VA6AW Ham Member QRZ Page

    Recently I have heard a number of operators using sdr rigs. Some sound great but others seem to have a rather irritating carrier that seems to be generated below the zero beat or spot frequency. Whats with this. I sure don't have a top quality receiver but I don't hear this type of signal on the older rigs that hams have been using for many years.

    Also the audio sounds muffled sometimes as if the operator is talking through a tube. No real fidelity if that's the way to describe it. I have listened to many fine stations such as W6CCP, W6ZR, N0UN etc and never heard this type of effect. Is this just a setup problem with this type of new rig.

  2. WD5GWY

    WD5GWY Ham Member QRZ Page

    That problem can appear with any radio that is not set up properly. It's nothing unique to
    SDR radios. What you might also be hearing, is someone with their transmit bandwidth set
    pretty wide (eSSB for one, or extra wide AM). With some SDR radios (Flex 5000 in particular) the transmit (and receive) bandwidth can be set up to 20Khz wide!
  3. VA6AW

    VA6AW Ham Member QRZ Page

    Tnx for the reply. Interesting about the bandwidth being set at 20 khz wide. Never heard of such a thing. Is that plus or minus the operating frequency. Been away from the hobby for so long these types of things are new info for me.

    I always understood that a minimum bandspread was required for ssb or cw. I remember getting a notification from a OO (OFFICIAL OBSERVER HI) back in the 70's stating my cw carrier was being heard below 14.000. I was working a VS5 in the all asian contest as I remember.

    Always watched out after that.

  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Not all OO reports are accurate, but maybe you were on 14.0003 and some of your signal really did appear below 14.000. No way to guess at that, now.

    Stations transmitting with "wide bandwidth" on SSB can often sound pretty lousy. I don't know why they do that, when all the voice information available can be transmitted within about a 3 kHz bandwidth; however here in the U.S., under FCC rules, there is no specific bandwidth limitation in the regulations.

    Maybe there should be. But, as yet, there isn't.

    FCC consider us largely "self regulating." If someone sounds crappy the best way to deal with that is to not answer them. If they go a long time getting no answers, they'll figure out something's wrong.:p
  5. VA6AW

    VA6AW Ham Member QRZ Page

    I have to admit I was very close to bottom of the band. My old rig was a yaesu pair FL/FRdx 400. No digital readout. Just an adjustable dial, which I calibrated on a xtal oscillator marker. The rig did drift so I was probably exceeding the band limit. Was a nice setup though, wish I still had it. Had that citation for many years but now cant find it.

    Still, with these new radios one would think that some enforcement would call for a minimum bandwidth on a crowded band. Not that means much as 20 meters was virtually dead up here today.

  6. WD5ABC

    WD5ABC Ham Member QRZ Page

    SDR radios eliminate the carrier and opposite sideband with software. If there's something showing up on the opposite sideband it's likely a problem with the setup in the software. The Flex radios have a built-in routine to do it, you just click a box and let it go for a few seconds. You should never have to do it but it's there if you suspect there's a problem. With the kits like the softrocks you do it manually in the software. I've had a Flex 3000 for a year and a half and a Flex 1500 before that and never had a problem with opposite sideband rejection on either one.

    The transmit audio is the same problem as analog rigs, it's just got to be set up correctly.

    Kerry, WD5ABC
  7. K0RGR

    K0RGR Premium Subscriber QRZ Page

    Are you sure they're doing SSB? The SDRs are getting popular for AM. Also someone wrote the software to put the Flex rigs on ACSB - Amplitude Compandored Sideband - the mode that was supposed to revolutionize ham radio a few decades ago, but never did. ACSB let you compress the SSB signal into a much narrower bandwidth, and a 'pilot carrier' was sent to assist tuning.
  8. N0SYA

    N0SYA Ham Member QRZ Page

    I have often wondered the same, as I have the idea that there is no carrier needed for the sdr rigs to create an ssb signal.
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    All modern rigs (that I can think of) both generate and demodulate signals using DSP. The days of "balanced modulators" and "product detectors" and such are past.

    SDRs are DSP engines with user programmable flexibility, really. The majority of modern gear really is already software-defined, but there are many ways to approach that.

    Hardware has recurring expense, software (other than upgrades and support) doesn't.
  10. WD5GWY

    WD5GWY Ham Member QRZ Page

    It's plus and minus 10Khz on either side of the center frequency. I know of one guy that's done that to
    annoy contesters who were nudging right up against a group that meets regularly on a particular frequency
    on 40 meters. His audio sounded pretty bad until I widened mine enough to get most of it. (using a Flex 1500 which cannot go as wide as the 5000) But, like WB2WIK says, most of the information (audio) can be had
    with 3Khz. No need for more. But, as he stated, there is no regulation preventing it. I don't see a problem with it on an uncrowded band. But, that is becoming a rare thing on the lower HF bands. On 10 meters, I have heard several Flex users on AM running pretty wide signals. Some sounded great and others not so great.
    It is interesting how much time and effort, not to mention money some people tie up in audio gear for SSB operation. For AM or FM, I can see that much more. For SSB, not so much. A clear, clean signal is much easier to listen to in my opinion.
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