Reduce BCI on CW pixie kit

Discussion in 'Homebrew and Kit Projects' started by K3RW, Mar 2, 2016.

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  1. K3RW

    K3RW Ham Member QRZ Page

    I've built two working kits (out of 4 tries--really working to improve soldering skills so I ordered 7, thinking I might get 3 working ones).

    One kit is the 4.1--which has a beeper sidetone for CW.

    The other is the more standard Chinese kit without the beeper, and a slightly different board setup, but basically the same parts/kit/etc. than the other one.

    Well, anyways, I am hearing slight 40m noise on the 'beeper one' on the end-fed antenna, and barely detectable 40m noise on the 80-10 trap dipole. However, the AM broadcast towers are nearly LOS from here, mounted on the West Hills above Portland, and they come in really strong. I'd guess there are at least a dozen there, though I am hearing one particularly strong.

    Is there a trick to reducing or eliminating this AM interference? I'm presuming it is AM anyways. Good 'ole Clark Howard was playing.

    Some are saying use ferrite beads, others are saying a metal enclosure, etc. I'm not familiar with the ferrite bead technique--but something I read said the guy put them on the power supply line, the headphones line, and somewhere else. I'll have to figure out where to get ones 'that small', unless I can wind the line through like a choke on a big ferrite.

    The trap dipole has a bunch of ferrite core things on it right after the tuner--the big clamshell 1" ones--I think there are 6. The end fed doesn't appear to have any. The trap dipole was much louder than the end-fed, and boosted the BCI with it just as much.

    So far I am admiring overcoming the tiny components and hoping to learn CW this way with a straight key, and not expecting much in the way of QSOs. If my dad can hear me across town I'll consider it a success. Not sure if the BCI screws up my TX to someone, or if it is just screwing up my RX.

  2. G3YRO

    G3YRO Ham Member QRZ Page

    Can't believe how cheap they sell those Kits !

    Given how near those transmitters are, you may have problems trying to lose the breakthrough!

    The problem is that this is a TRF receiver with only one very simple tuned circuit in the front end, that's the only thing stopping signals on ANY frequency being received.

    Firstly, I would put the board in a metal case (an old tobacco tin would have been ideal, but don't think they come in tins any more!). But most electronic shops sell a variety of small aluminium cases . . . you may find something online.

    Adding High-Q filtering on the receiver front end is a bit of a problem, as it is also in the transmit output path . . . but you could add another L and C on the input (same values) and see if that helps.

    You could also put a parallel tuned circuit tuned to the strongest broadcast signal in series with the aerial.

    Roger G3YRO
    KA9UCN and K3RW like this.
  3. N7EKU

    N7EKU Ham Member QRZ Page

    Hi Gregory,

    Even the US sourced kits can suffer from this problem due to the simple front end filtering. Ferrites on the power supply may help a bit, but probably not much. A current balun may help on pickup from your feedline and may help, but really depends on your antenna. Neither of these is a great help, as what is really needed is more front-end filtering:

    Kitsandparts used to offer one, but it's discontinued. You could homebrew it on a blank piece of PCB though as the circuit is so simple:

    Minikits has some currently offered and shipping isn't too horrible to the US or Canada:

    Cheers and 73,

    Mark -- n7eku/ve3
    K3RW likes this.
  4. K3RW

    K3RW Ham Member QRZ Page

    Thanks for the info--and thanks for the link!

    I figured if I could get away from the towers that might help, but then I'd probably just be in a 40m black hole too. Go up to a mountain to get good propagation, then probably get better AM signals (rrrr). The metro area is surrounded by AM towers--so the bandpass filter looks like a worthy project. I've never wound torroids before so I guess I should start now! If anything, I didn't expect much from the kit except to improve soldering skills. I figured--screw up a few of these learning before screwing up a $50 kit.

    At least the 'beeper' version produces the sidetone so I can hear my sending. I took it over to my dad today and showed him, and started sending CQ on the keyer--and he said "Y.... O.....??" Got to work on my dots and dashes and spacing.

    Problem with the kit (there are many but its cheap) is that it is 7.023--fixed, and that's right in the US Extra portion. So not a lot to talk to anyway, and with mW its a stretch to think I'll work any DX with it. But a fun project. Didn't burn myself with the iron so I did a few things right, and I got good at counting resistor bands. Some people put in a socket holder and switch them out with a bunch of crystals--that's smart.

    What I would really like is a CW kit that I can run through a PC interface and use on Fldigi. I use that for my CW stuff now, and I figure that helps me learn CW and helps pull out weaker signals when there is a lot of noise. But haven't seen such a thing--I would guess it would be a SSB kit, and it would have to have a data cable capable of running the SignaLink box... and $300 later I have basically the same capability that I did with the ICOM.

    I saw some guy on the internet did a Raspberry Pi thing with one of these. I might try that too. I've had one in a box for a year and need to learn how to use it.

    Many thanks--hope to see you all on the airwaves soon!
  5. N4STG

    N4STG Ham Member QRZ Page

    You just need a cable and a pot in series to the audio in on the PC. I do this with my HB-1A. FLDIGI manual has a keyer circuit to use an audio out channel to send CW from fldigi to your radios key input. I wired this across my straight key for when some speed demon shows up.
  6. K3RW

    K3RW Ham Member QRZ Page

    Is that something I could mod/add to a kit--not just the CW Pixie, but say any radio without a data port?

    I do like the idea of 'checking my work' using a CW program, and not having somebody scratching their head due to my shaky hand, poor spacing, and messing up left and right. So far I've used Fldigi to tx/rx CW, and hearing it key the rig to what I'm sending helps me get the spacing down. I'm not copying well at all because lowest speed I've ever seen was 16wpm, and low to upper 20s routinely.

    I just checked out the Youkits--neat stuff. Relatively easy to build for a newbie? Looking at the boards I can't tell if these little things press into sockets or are the kind that you have to cook in an oven :eek:
  7. N4STG

    N4STG Ham Member QRZ Page

    Yes, if you build the adapter from the manual you can use the output from the adapter to key any rig via its key input.

    During contests I use CWskimmer to decode. It makes figuring out the DX stations listening behavior a lot easier, but so should fldigi. I like using fldigi to send for fast code, but it does not decode very well in my opinion.
  8. W1VT

    W1VT Ham Member QRZ Page

    Roy, W7EL found that you could get rid of AM detection by using a doubly balanced diode mixer as a product detector and using a diplexer to keep the RF out of the audio stages so your audio amplifier didn't act as an AM detector. He designed a 40M receiver at a time when hams had to deal with foreign broadcast stations in the RF passband.

    In your case, an alternative technique is to adequately filter the broadcast signals from getting to the radio circuitry.

    Zack W1VT
    Last edited: Mar 14, 2016
  9. K8JD

    K8JD Ham Member QRZ Page

    You are in a tough neighborhood for MW AM interference. you have two 50 KW transmitter sites one on 860 about 3 miles North and another on 1080 KHz about 3 mi South of you !
    I just listed the first two big stations I found near you but there may be plenty of other lower power signals near you. (another bunch of 3 50 kW stations' sites about 13 miles south of you)
    I happen to have one 30M QRP rig that gets a terrible whistle from a SWBC station in HAVANA CUBA (1350 miles away from me) operating all night right in the center of the 6.0 MHz IF passband ! I had to build a 30M dipole to solve the problem that I had using a 40m ant and tuner for 30M. ,
    I am lucky that of the 15 or so, AM transmitters in the Detroit metro area, the closest ones are about 18 miles from my QTH !
    Last edited: Mar 14, 2016
  10. K3RW

    K3RW Ham Member QRZ Page

    Thanks--I'll try that and see what happens. I never thought I'd be hearing Clark Howard loud and clear on 40m :mad:

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