# Quagi antenna

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KA0EIV, Nov 2, 2016.

1. ### WW1WWHam MemberQRZ Page

If you run power it will overheat. This is why no commercial vendors use ferrite at VHF and up.

2. ### N0NBSubscriberQRZ Page

As I see it, the use of THHN wire is not a good choice for long term exposure to uV rays. In my experience, after a few years the outer clear insulation layer breaks down and becomes brittle allowing moisture between it and the colored, presumably PVC, insulation and eventually it flakes off. When I put something up I want to use materials that will last a minimum of ten years of uV exposure.

W0BTU likes this.
3. ### W0BTUHam MemberQRZ Page

Last edited: Nov 6, 2016
4. ### W1VTHam MemberQRZ Page

Looks like nobody has a useful methodology for improving designs.

As I see it, computer modeling can be very accurate in predicted how your design will work,
but cant really provide any guidance in what you can do to make the design better.
Equations can often provide guidance--even simplified ones can suggest which way to go.
A standard calculus exercise is taking an equation and solving for the maximum and minimum
values--just what we need to calculate the maximum gain of an antenna.

But, nobody I know can solve the equations for even a moderately sized Quagi.

Zack W1VT

5. ### K9STHPlatinum SubscriberVolunteer ModeratorPlatinum SubscriberQRZ Page

VT:

The old YagiMax program had a feature that allowed a maximization of the design. Well, suggested changes to maximize.

Glen, K9STH

6. ### W1VTHam MemberQRZ Page

There may be another approach for a highly skilled programmer--computers have gotten so advanced compared to what we had 30 years ago that we may be able to just calculate an entire collection of designs and choose the best one! For instance, we might assume that any real design will have all lengths rounded off to the nearest 1/32th of an inch. This reasonable approximation may result in a finite number of designs to calculate.

Zack W1VT

KA0HCP likes this.
7. ### KK4YWNHam MemberQRZ Page

Thanks for the link. Thats good reading.

In an earlier pdf, there are charts extending to 1ghz. The 43 mix seems ideal at 2m with 3 turns, with impedance dropping off as turns are added/subtracted.

I upgraded computers and haven't moved vna software to the new machine, so I can't validate. Hopefully I'll finish moving things this weekend and can continue experimenting.

8. ### AI3VHam MemberQRZ Page

Somewhat off topic, but ferrite is extremely common in microwave equipment.

It is common in devices called isolators and circulators.

Typically it is biased with a permanent magnet to make it unidirectional to rf.

I agree that the use of ferrites in microwave antennas is rare.

Rege

Edit: if adding ferrites to your vhf/UHF yagi makes a difference you have a defective yagi. Just like a ferrite isolator is a band-aid at microwave frequency's , ferrite at lower frequency's is covering up a problem. Its getting hot because its absorbing power that shouldn't be on the wire in the first place.

Last edited: Nov 8, 2016
9. ### WD5HHHHam MemberQRZ Page

KF6A,

Earlier in the thread I asked about the dimensions of the optimized quagi that is in the last post of the first page (9th reply). You reference the VE3SQB calculator. That however gives the 163+ inch quagi and not the 154 inch one that you refer to as optimized. Where would one find the dimensions for the optimized quagi?

My interest in the quagi is relative ease of finding suitable materials to build it with and the relative ease of getting it tuned. I can go to the big box building supply stores or the local lumber yard and welding supply to get what I need for a quagi. I would need to drive 50 to 100 miles (one way) to get the proper and affordable materials to build a yagi. I do have the insulators to build various G0SKC lfa yagi antennas but the materials are the problem. The tuning of the lfa yagis is simple also as it only involves adjusting the length of the driven element.

10. ### W1VTHam MemberQRZ Page

I thought the 154" antenna is a Yagi, not an easy to build Quagi.