Skip to content
View in the app

A better way to browse. Learn more.

Ham Radio Base -Powered By Ham CQ DX

A full-screen app on your home screen with push notifications, badges and more.

To install this app on iOS and iPadOS
  1. Tap the Share icon in Safari
  2. Scroll the menu and tap Add to Home Screen.
  3. Tap Add in the top-right corner.
To install this app on Android
  1. Tap the 3-dot menu (⋮) in the top-right corner of the browser.
  2. Tap Add to Home screen or Install app.
  3. Confirm by tapping Install.
Solar
SFI 125
SN 85
A 7
K 0 Quiet
X-Ray C1.2
Wind 424.4 km/s
Aurora 1
Updated 04:30 UTC HamQSL · N0NBH
Day 80/40m Fair 30/20m Good 17/15m Good 12/10m Fair
Night 80/40m Good 30/20m Good 17/15m Good 12/10m Poor

Callsign Lookup
_
Vanity Call Signs Available
Enter filters above and click Search.
ⓘ Callsign lookups are in real time via the FCC database. Vanity callsign availability is refreshed daily at 6:00 AM CST. The vanity search may be unavailable for a few minutes during this update.
Live DX spots
Live DX Spots — 70cm via PSKReporter · scroll or pinch to zoom
Band
Mode
Time
Loading map data…
MHz DX Spotter Info
Recent spots
Select a band above to load spots
Ready — select a band to fetch live spots

built my first dipole from scratch, swr is weird on one end of the band

 Loading...

so i finally got around to building a dipole instead of buying one, figured how hard can it be right. cut it for 40m using the 468/f formula, ended up with each leg around 33.3 feet, fed it with some RG-8X i had laying around and a center insulator i made from a piece of cutting board i cut up (yeah i know). hoisted it up in an inverted V config with the apex at maybe 30 feet, legs angled down to about 8 feet at the ends.

heres the weird part — swr is like 1.4:1 right at the resonant point which is sitting around 7.150 but then on the low end of the band around 7.020 it climbs to almost 2.8:1. i kind of expected some rise but not that much. on the high end around 7.250 its maybe 2.1:1 which seems more normal to me. is this asymmetry typical for inverted V or did i screw something up with the feedpoint? the legs arent exactly the same angle because of how my trees are positioned, one side drops steeper than the other.

using an SDR to check the swr curve, not a fancy antenna analyzer, so theres some margin for error i guess but it seems pretty consistent.

  • Replies 1
  • Views 16
  • Created
  • Last Reply

Top Posters In This Topic

Featured Replies

the unequal leg angles will do that, you've basically got slightly different effective electrical lengths on each side once the geometry changes. the steeper leg is closer to vertical so it acts a bit shorter electrically and shifts things around. not a huge deal for operating but it'll skew that swr curve. you could try trimming the higher end leg just a tiny bit and see if it evens out, or honestly just stick a 1:1 current balun at the feedpoint if you havent already — that'll help with common mode stuff that might be messing with your readings too. whats your coax run length? sometimes with RG-8X you get some weird impedance transformation depending on the electrical length of the feedline and that can make the swr look lumpy in ways that arent actually the antenna.

i built almost the exact same thing last spring and had similar swr shape. mine turned out to be the feedline acting up more than the antenna itself. i added a choke balun like 5 turns of coax through a FT240-43 toroid right at the feedpoint and the curve got way more symetrical. also 30 feet apex on 40m inverted V is a little low, the angle of the legs affects the radiation angle and also the feedpoint impedance dips below 50 ohms when the legs get steep, so youre not really feeding a 50 ohm load anymore. some people use a 4:1 balun for inverted V specifically because of this but honestly at 2.8:1 most rigs and tuners wont even care, mine handles it fine.

  • Guest locked, pinned, unpinned and unlocked this topic

Join the conversation

You are posting as a guest. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

Account

Navigation

Search

Search

Configure browser push notifications

Chrome (Android)
  1. Tap the lock icon next to the address bar.
  2. Tap Permissions → Notifications.
  3. Adjust your preference.
Chrome (Desktop)
  1. Click the padlock icon in the address bar.
  2. Select Site settings.
  3. Find Notifications and adjust your preference.