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Capacitors

Discussion in 'Homebrew and Kit Projects' started by KE0M, Aug 20, 2008.

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  1. N0WVA

    N0WVA Ham Member QRZ Page

    Check out Toroid King. I think he carries a good selection of NPO's at a good price.
     
  2. AC0FP

    AC0FP Ham Member QRZ Page

    It would help if you told us what you need, give the values AND whether they are uF or pF with the TC required for that particular part. How many might help also.

    73,

    Frank:)
     
  3. KC0ZJZ

    KC0ZJZ Ham Member QRZ Page

    That would be http://www.kitsandparts.com/

    I've ordered from him a few times, good results, prompt shipping.
    Capacitors http://www.kitsandparts.com/capacitors.php
    In NP0 he has a 10ea kit for $20 and a 25ea kit for $40 (475 pcs)

    Also I see Hendricks QRP Kits also has a nice cap kit.
    http://www.qrpkits.com/capkit.html
    $50 for 650 pcs, 25 ea value. This one has more values, goes upto 1000 pf in NP0 and also has 0.01uF and 0.1uF in X7R.

    Roger
    .
     
  4. K8ERV

    K8ERV QRZ Member QRZ Page

    I will check today, but the .1 and .22 (pf) look like typos.

    TOM K8ERV Montrose Colo
     
  5. AC0FP

    AC0FP Ham Member QRZ Page

    Dollars to donuts you will find .1 and .22 are uF. There are .1 & .22 pF caps made but experimenters can't buy them and even fewer people have them.

    73,

    Frank:)
     
  6. KE0M

    KE0M Ham Member QRZ Page

    Sorry, I am trying to build a direct conversion receiver out of the book Experimental Methods in RF Design and they are not very specific on the capacitor values and this is my first time building from a schematic. I know now that the .22 and .1 are uf but I don't know about the rest. Does anybody know of the IC based direct conversion receiver in the book that I mentioned above?
     
  7. K5UOS

    K5UOS Ham Member QRZ Page

    The book is great for beginner and experienced builders but does assume some background. The RX is a good 1st project.

    The capacitors from the EMRFD Chapter 1 DC receiver ( I assume this is the RX) are as follows:

    Input Circuit
    47pF Can be almost any type of ceramic. I suggest NPO/COG from Mouser.
    180pF (this is variable compression trimmer cap approx 10pF to 180pF).
    270pF Can be almost any type. I suggest NPO/COG from Mouser.

    Note: W7ZOI is using an old dogbone type of cap for the 47pF so I believe he was just picking out of the junk box and using whatever he found first.

    If you can't find a 180 pF compression trimmer, find something close and change the 270pF to equal approx 360pF with the substitute variable at half setting. L1 is approx 1.2uH. If you change the trimmer you may need to change L1 by adjusting turns but it tunes very broad so no adjustment is likely. The trimmer capacitor will likely be set and left as you peak it on initial tune up. A very simple trimmer is all that is needed and there are many options.

    VBFO (the main oscillator)
    2 - NPO 680pF (feedback capacitors for the onboard oscillator in the NE602)
    270pF (NPO)
    50pF (C2 is a variable)
    10pF (NPO)
    33pF (NPO)
    200pF (NPO)
    80pF (C1 is variable)

    The variables are the two capacitors with knobs in Fig 1.1 and will likely take time to find two good ones. I see them on EBAY all the time. You can get by with only one. The two are an old scheme called band set and band spread. Most of the others are fixed padder capacitors.

    The .22 and .1 caps are in uF. I would use inexpensive metalized polyester film or the KEMET multilayer ceramic caps (both from Mouser) for the .22 uF and use any .1 uF type.

    The 4.7uF pin 1 to 8 on the LM386 sets the gain of the audio amp. The 100uF caps are the supply decoupling capacitors and can be greater in value.

    All others are marked. The text does list most of the cap values and describes most of what I state above.

    This receiver is a nice 1st project and could be a product detector and audio amp for a simple superhet. Experience will show you that considerable substitution is possible for most of the parts above.

    The best of luck on your project. 73 K5UOS
     
  8. VK2TIL

    VK2TIL Ham Member QRZ Page

    It sounds as if you are building the NE602/LM386 receiver described in chapter 1.5 of EMRFD.

    A good project.

    Read what the author has to say about caps (to the right of fig. 1.9).

    The convention for capacitors is that values in picofarads (pF) are shown as a whole number (22, 470 etc) and values in microfarads (uF) are shown as a decimal (0.1, 0.22 etc).

    Sometimes the leading zero is omitted, eg .1, .22 etc. This is poor practice as the decimal point can easily be missed.

    You will see good & bad practice in fig 1.9.

    One cap is shown as 0.1 whilst another is shown as .1.

    Electrolytics are shown as XXXuF; this distinguishes them from XXX pF units. The presence of a "+" is also indicative of an electrolytic or tantalum.

    So; all capacitors in fig 1.9 are in pF, excepting;

    Four electrolytic or tantalum types (we know this because each has a "+" on the diagram);

    Three 0.1 uF caps; these are bypass components and NP0 is not necessary, ordinary ceramics are OK;

    The three caps to the right of the '602.

    As a general rule, any ceramic capacitor associated with a tuned circuit should be NP0; look on the left and also below the '602. The exception is the ".1"; it is just a bypass to bring pin 2 to RF (but not DC) ground.

    The capacitors to the right of the '602 pass audio so almost any kind will do; plastic types ("greencap", mylar etc) are usual but ceramics are OK.

    There is an EMRFD group at;

    http://groups.yahoo.com/group/emrfd/messages

    W7ZOI's website is also useful;

    http://w7zoi.net/w7zoi_site.html

    EMRFD is a wonderful book; I hope it gives you a lot of fun & knowledge.
     
    Last edited: Aug 23, 2008
  9. VK2TIL

    VK2TIL Ham Member QRZ Page

    My mate UOS & I posted almost simultaneously!!

    He has covered the matter in some detail; between his post & mine you should have plenty of information.
     
  10. K5UOS

    K5UOS Ham Member QRZ Page

    Kerry...you know, I was thinking about what you might say when I was writing my answer!! I know how much you and I enjoy the book.

    I have a great respect for DC receivers particularly those in Chapter 8 which have amazingly clean audio and make such good PD/audio sections for high performance superhets. I was excited to see ke0m building one.

    73 K5UOS
     
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