(Now a bi-weekly program)

October 16, 2012

Join the "CWTD Yahoo Group" for email discussion in between our weekly sessions by clicking here.

Homebrewing VHF/UHF Antennas


In this episode we discuss and illustrate examples of getting on the air with 6m, 2m and 70cm (440 MHz).  Most of us know the "mechanics" of HF operation, but VHF and UHF throw some interesting curves at us as far as propagation, feedlines and losses, antenna polarization, power levels, terrestrial impediments, and more.  Everything from HTs to mobile rigs, to base stations. And every kind of operation: FM repeaters; point-to-point using FM, SSB and CW; weak signal propagation; satellites; EME and more.  

73, George N2APB  & Joe N2CX

Audio Recording ... (Listen to the MP3 podcast)

Discussion Notes:

<20:32:00> "Joe N2CX": Marc Franco's MP3 interviews are not on the whiteboard.
<20:46:34> "Alan W2AEW": I have a picture on mine
<20:46:46> "George - N2APB": Me too!
<20:55:54> "Ray K2ULR": PL is also called CTCSS Continuous Tone coded squelch system
<20:56:10> "John ZL1AZS": To add your pic to the right-hand panel (with your name selected in the left panel) right-click your name and go to Select Avatar, choose a pic from your local hard drive and Voila!
<20:56:56> "Ken - VA3KMD": Joe; what's the upper frequency limit of the N2CX choke balun kit?
<20:57:41> "Joe N2CX": I've charazcterized it up to 6 meters. A different ferrite core would make it usable up on higher frequencies.
<20:58:02> "Joe N2CX": John, thanks for the phot ino!
<20:58:47> "Ken - VA3KMD": Thanks Joe
<21:00:02> "Joe N2CX": Alan you need to escape from that Tektronix prison!
<21:00:56> "Alan W2AEW": sometimes I reeeeallly get into my work!
<21:01:21> "Terry WB4JFI": I belive microwave ovens are around 2455MHz, and can have high-power maggies.
<21:01:58> "Joe N2CX": Hmmm is that pix what you call a green screen?
<21:02:31> "Alan W2AEW": uWave ovens are indeed in the 2.40 to 2.50GHz frequency range - the same as the 2.4GHz ISM band used for WLAN, Bluetooth, etc.
<21:03:38> "Terry WB4JFI": microwvae ovens operate (hopefully) at the resonant freq of water molecules
<21:15:49> "Ken - VA3KMD": The Arrow Antenna 2m/70cm Jpole @ $40 works well for me.
<21:18:36> "Terry WB4JFI": Skip Teller has had several good articles in QST about homebrewing 2M and 440 antennas of various types. Low cost, fairly easily found parts, and most are collapsable & easily transportable.
<21:20:08> "Clint ka7oei": A bad antenna outside fed with mediocre coax will almost always beat a decent antenna indoors... (building materials impose 10-20 dB loss - far more than a likely coax run!)
<21:21:08> "Frank N3PUU": but dont be afraid to run whatever you can.. my most memorable contact was NJ to vancouver island on 6 meters using a 6 meter dipole in my attic!
<21:21:22> "Clint ka7oei": RG-6
<21:22:08> "Alan W2AEW": my pic is taken by convertng NTSC video from my camera to X, Y and Z drive signals for my scope, and thus displaying composite video on the scope. Then, I took a picture of that
<21:22:17> "Clint ka7oei": oops RG6 TV coax works surprisingly well - the impedance mismatch isn't really that big of a deal when it comes down to it: Tha adapters will probably cost more than the coax run
<21:25:41> "George - N2APB": Great point Clint. Often the TV coax can be found locally.
<21:25:45> "Clint ka7oei": oops RG6 TV coax works surprisingly well - the impedance mismatch isn't really that big of a deal when it comes down to it: Tha adapters will probably cost more than the coax run
<21:26:20> "Clint ka7oei": (Sorry - i was typing and forgot to mute the mic - and spacebar toggles the mic...)
<21:26:23> "Paul PA1TAS": Great show thou and was late in but great as always thank you very much from Holland
<21:26:48> "Frank N3PUU": Thanks guys, great job! See you on saturday.


So, where are we talking about in the spectrum? ...   




1) What do you want to be doing on VHF & UHF?

FM Communications

- Hand, portable, mobile operation


- Most newcomers these days start off here

- Paths:

        - Line of sight

        - Some tropospheric ... "inversion!"


Weak Signal Communications

- Fixed, point-to-point operation

- SSB and CW


- Enhanced VHF/UHF rigs, antennas, power ...


- Paths:


        - Line of sight



        - Tropospheric Ducting ... http://electriciantraining.tpub.com/14182/css/14182_96.htm




        - Meteor Scatter ... http://en.wikipedia.org/wiki/Meteor_burst_communications


        - Ionispheric Propagation ... http://users.picknowl.com.au/~wavetel/propagation

  • The ionosphere is important for radio wave propagation....

  • ionosphere is composed of the D, E, and F layers

  • the D layer is good at absorbing AM radio waves

  • D layer disappears at night.... the E and F layers bounce the waves back to the earth

  • this explains why radio stations adjust their power output at sunset and sunrise


        - Earth-Moon-Earth (EME)

Hams utilize EME for two-way communications. EME presents significant challenges to amateur operators interested in working weak signal communications. Currently, EME provides the longest communications path any two stations on Earth can utilize for bi-directional communications.

Amateur operations use VHF, UHF and microwave frequencies. All amateur frequency bands from 50 MHz to 47 GHz have been used successfully, but most EME communications are on the 2 meter, 70-centimeter, or 23-centimeter bands. Common modulation modes utilized by amateurs are continuous wave with Morse Code, digital (JT65) and when the link budgets allow, voice.

Recent advances in digital signal processing have allowed EME contacts, admittedly with low data rate, to take place with powers in the order of 100 Watts and a single Yagi antenna.

      Marc N2UO


2) What is Polarization?


          Video comparing vertical and horizontal polarization: http://www.youtube.com/watch?v=S-oeFQ6LvdE


Think of polarized sunglasses ... What are the benefits?



Cross-polarization loss ~ 20dB


        - E-Ham discussion on cross-polarization loss: http://www.eham.net/ehamforum/smf/index.php?topic=14857.0;wap2


Q1:  What polarization are sunglasses? 

Q2:  Why are LCD screens hard to read while wearing polarized sunglasses?  (iPad, mobile phones, etc.)


Circular Polarization ... we won't go there ...




3) Height

Higher the better!

Mostly line of sight communications

    - Why are repeaters usually located on hilltops?

                     Radio Mobile web site (Line of Site/Nape of the Earth VHF propagation): http://www.cplus.org/rmw/english1.html


   30 MHz path between N2CX ("map pin 1" in Brooklawn, NJ) and N2APB ("map pin 2" in Forest Hill, MD)


   30 MHz propagation probabilities from QTH of N2CX, based on terrain and elevation



                   146 MHz propagation probabilities from QTH of N2CX, based on terrain and elevation



4) Repeaters

Good repeater reference ... ARRL: 


PL Tones ...

    - sub-audible tones

    - control

    - access


Old days ..."Repeater Wars":  A higher-power station would key up multiple repeaters


Nowadays ...

    - Analog and digital PL tones

    - Provide access only to "your" repeater


Linked Repeaters

    - accessible by a sequence of PL tones

5) Feedline Decoupling

Properly coupling energy to the antenna


- Feedline Blaun

- Gamma Match

- Choke Balun

6) Power Levels

Lower Power (1-5w):  HTs ... maximize battery life, minimize brain fry

Medium Power (10-20w): Satellite rigs

Moderate Power (20-50w): Mobile rigs ... got to hit the repeaters with marginal/compromises antennas on the auto

High Power (100w): Base stations ... distant repeaters and VHF contesting

Higher Power (1 kw): Multi-band/multi-mode base stations for EME and weak signal propagation


Higher power used by stations trying to maximize line-of-sight paths PLUS scattering over the horizon



7) Safety

Radar range next to head ... "brain fry"

Rule of thumb(?):  "Stay 30 feet away from any active VHF/UHF antenna"


8) Feedline Loss

More of a need for good coax

        - Dialectric + ohmic loss

        - More air in dialectric = lower loss

                - Foam is good for VHF

                - Hardline: "spiraling dialectric"




9) Antenna Types



        - 1/4-wave Vertical




        - 5/8-wave Vertical





        - Zepp  (which is "end-fed", by definition!)









    - See below!

10) Let's Build!


6m Moxon ...  http://www.moxonantennaproject.com/n2mh/n2mh.htm



Who the heck IS this guy???  (N2APB holding his 6m Moxon beam)



2m Yagi




W7ZOI:  "This simple 7 element Yagi is ideal for portable operation. The elements can be removed and replaced in a few minutes. The 2.42 Metre boom will fit inside my car. All of the elements are made from 6mm solid aluminum rod. The boom is made from 50x25mm (2x1 in) timber."






2m/70cm J-Pole


This project taken from QST September 1994 is about a vertical dual-band antenna for 144 and 430 MHz made with a TV twin lead and coax cable ... jpole-dual-band.pdf








1.    EI9GQ Portable 7-el yagi for 2 meters:    http://homepage.eircom.net/~ei9gq/yagi.html

2.    VK1OD “Matching a 5/8 wave vertical http://vk1od.net/antenna/FiveEighth/match.htm

3.    A Plethora of J-Pole designs: http://www.pcacs.org/j-pole_designs.htm

4.    Cheap and Simple VHF/UHF Yagis: http://www.mydarc.de/dk7zb/PVC-Yagis/PVC-details.htm

5.    6 Meter Moxon: http://www.moxonantennaproject.com/n2mh/n2mh.htm

6.    VK1OD “A narrowband current balun using coax line sections” http://vk1od.net/balun/I4BBE/index.htm

7.    E-Ham discussion on cross-polarization loss: http://www.eham.net/ehamforum/smf/index.php?topic=14857.0;wap2

8.    Video comparing vertical and horizontal polarization: http://www.youtube.com/watch?v=S-oeFQ6LvdE

9.    The Basics of VHF and UHF Signal Propagation: http://www.dxfm.com/Content/propagation.htm

10. Radio Mobile web site (Line of Site/Nape of the Earth VHF propagation): http://www.cplus.org/rmw/english1.html

11. 6M The Magic Band:  http://members.shaw.ca/ve7sl/magic.html

12. Weak Signal Propagation ... http://www.google.com/imgres?q=weak+signal+radio&um=1&hl=en&biw=1251&bih=833&tbm=isch&tbnid=N_109eec9etQfM:&imgrefurl=http://www.docstoc.com/docs/54228703/VHF-Weak-Signal-Operation&docid=L72m4sLuK_ZhRM&imgurl=http://img.docstoccdn.com/thumb/orig/54228703.png&w=1500&h=1125&ei=_I17ULGgLbGQ0QGn3YHwDw&zoom=1&iact=hc&vpx=564&vpy=51&dur=2651&hovh=194&hovw=259&tx=150&ty=95&sig=102702853584817466419&page=1&tbnh=145&tbnw=194&start=0&ndsp=28&ved=1t:429,r:2,s:0,i:74



Back to CWTD Home