Which Type Of Coaxial Cable For QRP ?

Discussion in 'QRP Corner' started by KD9FRR, Jun 20, 2017.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Left-3
ad: MessiPaoloni-1
ad: L-MFJ
ad: Subscribe
ad: K5AB-Elect-1
  1. KD9FRR

    KD9FRR Ham Member QRZ Page

    What type/size of coaxial cable do you suggest running for your QRP rigs ? I'm looking for QTH operation less than 100 feet, and mobile/field/backpack operation, in CW, phone, and digital modes, if it makes a difference.

    73's

    Fred
    KD9FRR
     
  2. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    People sometimes use cheaper, smaller coax for QRP when the fact is QRP is when you need the lowest loss you can get as every db counts. For fixed station use, use the lowest loss you can afford and use in your installation. Portable has different problems with weight and bulk and such, and runs are usually shorter, so some compromise may be in order.
     
    KF4ZKU, KU4X, KU3X and 1 other person like this.
  3. KU3X

    KU3X Ham Member QRZ Page

    I have to agree with Roger. For the primary station I would run RG 213 since you are talking about a 100 foot run. For portable, that will depend on how far away the antenna is?
    I operate QRP portable all summer long and I would never carry RG 213 around with me. RG 8X is pretty good and I use to use it all of the time. I did order some RG 58, with BNC's
    on both ends from, "Cables on Demand" and used it for a short time.
    Lately I use my 28 foot telescopic mast with a Hy Power Ant. Co. OCF40QM antenna fed with 35 feet of RG-174. The antenna is so small it can fit in your pocket. If there are trees close
    by, the mast is not needed.

    The best I can say, when it comes to portabe operations, you have to find the balance of minimal loss becasue of coax and antenna against how much you want to carry.
    The OCF40QM is a very efficient antenna and fits in your pocket so that part of the equation is resolved. Now we are down to coax length versus loss. Very short runs, 30 feet or less,
    there is nothing wrong with RG 174. Now address battery size. LiPo's are great for size, output voltage and amperage.

    http://www.ku3x.net/portable-qrp/elecraft-kx3

    Maybe the photos on this page may offer you some ideas?

    http://www.ku3x.net/p

    I don't suggest the 40 foot mast as shown on the bottom of the web page. Hi Hi

    Barry, KU3X
     
    KF4ZKU likes this.
  4. KG6LI

    KG6LI XML Subscriber QRZ Page

    Hi Fred,

    Like Barry, when in situations that I'm packing the ham gear I stick with the RG-174. It's light, can be packed away with a minimum of space, and for shorter runs the loss is negligible. I have a 25' section I use with the end-fed wires, and the 174 is pre-installed on the SOTAbeam linked dipole I use.... 73 de KG6LI
     
    KF4ZKU, WA7PRC and KU3X like this.
  5. KD9FRR

    KD9FRR Ham Member QRZ Page

    Thank you everyone for your input. This is exactly the information that I needed.

    73's

    Fred
    KD9FRR
     
  6. KD9FRR

    KD9FRR Ham Member QRZ Page

    Well, thats just great ! Thanks to Mark I've discovered SOTABeams..... and linked dipoles ! This could be really bad. It'll be fun though ! :D

    Fred
    KD9FRR
     
    KG6LI likes this.
  7. KM4DYX

    KM4DYX XML Subscriber QRZ Page

    Another option that can work well with QRP is to run a long wire out the nearest window from your tuner. A good counterpoise arrangement and you are in business without any coax. Worked for me. Also, I'm also a fan of RG174 and SOTAbeams for portable ops.
     
    KB7PWJ likes this.
  8. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    If you are going to use a tuner, it's hard to beat ladder line. Light and lower loss than coax, and with a balun in the tuner a lot less prone to RF floating around the shack or portable area (where it's harder to ground for it anyway) which end fed random wires are very prone to create. They do work though.
     
    Last edited: Jun 21, 2017
  9. W6OGC

    W6OGC Ham Member QRZ Page

    Just make sure the antenna, tuner and ladder line will work on the frequency(ies) to give a good match without hideous losses in the tuner. There are some combinations that are very lossey.

    DJ0IP has an excel spreadsheet with some interesting numbers http://www.dj0ip.de/app/download/5788321979/MATCHBOX+SHOOT-OUT+V.1.3_e97.xls
     
  10. KC8VWM

    KC8VWM Ham Member QRZ Page

    I find a good compromise between loss and bulk is LMR-240. It's basically the same diameter size as RG-58 but exhibits attenuation losses similar to much larger diameter RG-213.

    For example losses per 100/ft.

    RG-213 at 50 MHz = 1.6dB
    LMR-240 at 50 Mhz = 1.7dB

    LMR-240 datasheet: https://www.timesmicrowave.com/documents/resources/LMR-240.pdf
     

Share This Page