Elecraft K4

Discussion in 'Ham Radio Discussions' started by W6RZ, May 16, 2019.

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  1. SM0AOM

    SM0AOM Ham Member QRZ Page

    The plots below, from the mid-80s monograph "Großsignalverhalten von Kurzwellenempfänger" edited by the engineering staff of Telefunken-Deutsche Aerospace illustrate the effects of various IP2 and IP3 values when a receiver is exposed to a number of strong signals having negligible noise contribution themselves, both far from and near the wanted signal.

    The plot at the bottom was representative for the "flagship" of this era, the E1800A receiver.

    The noise-like structure of the spurious products generated in receivers with lower performance is easily seen in the top plot.

    IMD (2).JPG

    73/
    Karl-Arne
    SM0AOM
     
    Last edited: May 24, 2019
    N0TZU, NL7W and N2EY like this.
  2. KM1H

    KM1H Ham Member QRZ Page

    Just to be really clear this white noise is REALLY THERE and is a resultant of many transmitted IMD products and can also consist of RECEIVED phase noise artifacts.

    Whether or not it is received in ANY receiver is dependent upon band conditions, location, antennas, plus receiver MDS which could be reduced by internally generated phase noise and masking the white noise. With equal specs and receiver settings any receiver is capable of hearing it equally well.

    AND as I already stated:
    The industry has finally produced a preamp, in the TS-890S, which is actually useful for digging down into all new layers of signals, wanted and unwanted. I have stressed for about 4 decades that the RX noise figure on HF (and even on 80/160 with some exceptional low noise RX antennas) should be as low as 4dB and not the 12dB or more nonsense as published for decades in magazines, OTA, and even on various forums. Maybe Kenwood has heard my message:D:eek:

    With a good location (which I have), directional antennas with a very high F/R (that I designed and built) I have proven it over and over to myself and others who have been here or heard me working DX they couldnt hear. This station came in #1 in many contests or in the top 2-3 or so primarily because of attention to details. The propagation gods did not always cooperate as I was too far North at times to win. And the guest op or myself was not using the latest and most expensive gear (all bought used, modded, and maintained by myself) and automatic features as the competition who often was using "loaners" supplied by rig and amp companies. KM1H caused a lot of gnashing of teeth among all of those years I kept it up....I finally stopped as I made my point and it was getting boring. I also refused all equipment and financial assistance to build that WORLD CLASS STATION.

    KM1H was also the first to use a Digital Voice Recorder, the DVK-100, developed by my boss, N1BPO SK, and myself while at Wang Labs. We sketched it out on napkins one Saturday afternoon while consuming food and beer around his pool. Nel-Tech Labs was formed to become a major player in the industry and is now part of the PICA group.

    Carl
     
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  3. N2EY

    N2EY Premium Subscriber QRZ Page

    Exactly!

    Thanks, Karl-Arne!
     
  4. KM1H

    KM1H Ham Member QRZ Page

    No arguments there as in the 80's very little was mentioned about IP2 contributions. These days it is a known factor but with the huge drop off of SW broadcasting and other high power HF users the contribution is much less. Also remember that many countries on SW had very poor transmitted spectrum.

    With modern signal processing on TX and RX those IP2 issues are further minimized.

    Carl
     
  5. W6RZ

    W6RZ Premium Subscriber QRZ Page

    When I lived on the southern Maine coast in the late 70's, the SW broadcast signals were so strong on 7 MHz, they'd mix with the local AM station at 1400 kHz and leak into the 8.295 to 8.895 MHz IF of my Kenwood R-599D. They were not strong, but if I tuned a dead band like 10 meters at night, I could hear them.
     
  6. KM1H

    KM1H Ham Member QRZ Page

    When I lived in Lexington MA in the mid 60's and went to work for National Radio I rented some rooms in a real old house on top of a hill. The landlady's married and moved out son was a ham so she was open to my setting up a station. For 40M I installed a full size GP at the top of a 70' pine tree with about 8 radials tied to saltwater fishing sinkers and tossed over the branches.
    At night the SW BC was so strong my Drake 2B folded up and signal mixing was everywhere and I had to back the RF gain way down. In a CW contest it was even worse and I soon bought a filter loaded used Collins 75A4 and turned it into a real radio that I still use at times....7360 beam deflection mixers, hang AGC plus better timing, a bullet proof front end, cascaded filters and more. Years later I measured a 6dB NF on 10M.

    Push pull output amps were known to cancel (almost) the IP2 garbage as soon as Class B audio came along around 1932. PP SS output and driver stages in our rigs did the same and some of the better radios did that also in the RX amp such as my TS-940 and 950SD which were 80's designs. The end result is that I did not experience the IP2 problems but the white noise was obvious since I knew what to look for. I cant speak for other brands and models....altho I serviced many I do not remember that RX circuitry. RX mixer designs were also more advanced in the 80's. Possibly commercial designs in EU were not as advanced.
     
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  7. SM0AOM

    SM0AOM Ham Member QRZ Page

    IP2 was a very much understood and accounted for aspect of receiver design even before and during the 80s.

    The use of sub-octave or tracking-preselector filters and balanced lossless-feedback RF amplifiers in the signal paths of the higher-performance receiving systems of this era became a consequence.

    During the peak of the Cold War, the EU HF spectrum was packed with broadcast signals and jammers which were generating levels that really taxed the capabilities of the receivers of the day.

    As an employee of an organisation that operated several receiving sites for both fixed and mobileHF services, it was possible to gain some early insights into the problem and its consequences.

    When connecting a spectrum analyser to the rhombics or TCI 503 and 548 log-periodics beaming south during afternoons, it was common to observe many signals peaking in the -10 to 0 dBm, or more than 100 dB above the noise floor, range from the broadcasters.

    An "acid test", that quite few fielded receivers were able to pass, was to first tune to an un-occupied channel in the vicinity of 7 or 9 MHz , then injecting a weak wanted signal on this frequency via a directional coupler and measuring the SINAD before and after connecting the antenna. More often than not, this weak signal became completely wiped out by IM products even when using quite expensive receivers that lacked RF selectivity.

    This also taught the importance of using the RF gain and attenuator functions found in the better receivers, as the average observed antenna noise figures in these frequency ranges were at least in the 20-30 dB regions, and the use of an attenuator helped very much in reducing the influences of the high-level signals.

    Long before my time, receiver specialist B M Sosin at Marconi published a study of the real receiver performance attainable using various gain and selectivity distribution schemes in the presence of the RF environment prevalent in the 70s Europe.

    His findings, summarised in his contribution to the anthology "Radio Receivers" edited by William Gosling, very much influenced the contemporary design teams at the major receiver manufacturers.

    73/
    Karl-Arne
    SM0AOM
     
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  8. KD8TUT

    KD8TUT Platinum Subscriber Platinum Subscriber QRZ Page

    Yup.

    My guess, after asking that question in Dayton this year and in 2015, is that the companies don't think hams want the feature.That's the response.

    The other response I get about beam forming and phase cancellation is also "no". Flex used to have it on the 5000.

    They seem like no-brainer features to me. But then again I've experienced them operating. On paper they may not be that exciting.
     
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  9. K2XT

    K2XT Premium Subscriber QRZ Page

    We used to be able to solve our own problems. Now if we want something implemented we have to beg the manufacturers to "put it in the next release."
    The beam forming and phase cancellation is a fascinating feature to see in action. It makes a huge difference for the ham digging for a really weak one on 160, no doubt. Problem is, today the interest seems to be digital modes, remote operating, and stealth operating at HOAs.
    SmartSDR on Flex radios doesn't have the simplest, most basic feature that every radio made since 1978 has - an A/B vfo button. To flip between two frequencies you have to go through a 4 step process - mute the A vfo, unmute the B. Then the reverse. Absurd.
    Adaptive predistortion? Why would an alligator or contester want that feature? How would that help the contest score? I've heard contesters say they WANT a wide signal, heavily compressed. Keeps the riff-raf away!
     
  10. KM1H

    KM1H Ham Member QRZ Page

    Understood but little accomplished at the time.

    Invented a few miles from where I used to live:
    Norton, D.E. and A.F. Podell, “Transistor Amplifier with Impedance Matching Transformer,” US Patent 3,891,934, 24 June 1975

    Those are the preamps I referred to earlier and I still use them...simple and effective.

    Tracking preselector filters = tuneable front ends as in most tube era receivers as well as the various ham band only hybrids from Kenwood TS-520, etc.
    Also used in high end spectrum analyzers as an external option or built in.

    Im glad you referred to them as in the signal paths of the higher-performance receiving systems of this era became a consequence as those were not part of stand alone receivers. My experience with EU products was that Rhode & Schwarz was at the top of receiver design. I knew Dr. Ulrich Rhode very well after he moved to New Jersey and introduced him to PIN Diodes as replacements for the distortion generating generic diodes for octave switching filters and other areas in RX and TX paths. Since he already had a TS 440 I sent him a package. This was thru my decades long association with engineers at MACOM and their predecessors going back to the 60's. His stellar reputation convinced Yaesu to immediately start using them in production of existing products and other brands followed in new products. The reduction of internal RX IM products was substantial and just another reason my TS-940's performed so well in contests and DX pileups.

    There have been several tuneable preselectors offered for ham and general coverage that do wonders for reception, especially those in the "economy" class so favored by many:rolleyes:

    Carl
     
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