Another dumb yagi question, - Page 1
Forum section: electronics / rf-microwave

author: CaptDon
author_rank: Super Contributor
timestamp: May 28, 2025, 12:35:17 pm
content: I am wondering why the store bought UHF T.V. yagis seem to have elements 40% shorter than desired? I ran some numbers for 515 MHz on the Steeman yagi calculator website and the elements are predicted to be in the range of 10.5 to 11.5 inches with the reflector being the longest and the most distant director being the shortest. However both of my store bought UHF 'well recommended and tested' antennas have elements barely 6.75 inches in length. With the UHF 'repacking' for U.S. over the air frequencies everything was shifted toward the lower end of the original UHF television channels. It would seem longer elements would now be the norm? Would you predict any real advantage to replacing the 10mm diameter short director elements with the 40% longer elements? I am trying to get every possible dB of gain at the antenna possible. The yagi I am using is 11 elements and it at best has maybe 1db of gain above a similar 'short element' 6 element yagi. I want the most gain prior to the antenna mounted preamp. Any thoughts from you ham radio yagi homebrewers? I can't get above the tree line. Winter reception is good 98% of the time. Summer 'leaves on the trees' reception is only good 50% of the time. This concerns reception of one CBS channel which broadcasts at 1/5 of the power and is omnidirectional where the other stations that give solid reception have 5X the E.R.P. and a directional pattern suited to the target viewing areas. Thanks for your ideas and input!!

author: radiolistener
author_rank: Super Contributor
timestamp: May 28, 2025, 09:54:09 pm
content: for tv they can sell just piece of metal as antennaDid you tested it with VNA?

author: CaptDon
author_rank: Super Contributor
timestamp: May 28, 2025, 10:29:32 pm
content: I don't own a VNA, only the TinySA which I use to view signal strength. I will be able to compare signals if I do start replacing elements with the suggested yagi calculator lengths. I am just wondering if it will be worth my trouble to buy the 10mm tubing and start modifying. One problem that I have using the amplifier is overload from the much stronger stations. The ABC, NBC and PBS stations are running 500KW ERP in a directional pattern and I am in their target 'lobes'. The CBS station for some incredibly stupid reason is running 96KW ERP in an omni directional pattern. Maybe they would be interested in better market coverage with a translator 'out here in the boonies'?

author: MF-jockey
author_rank: Regular Contributor
timestamp: May 28, 2025, 10:35:58 pm
content: UHF TV Yagi antennas are typically designed for broadband, and antenna gain increases with frequency. The directors tend to be shorter. If one frequency is to be received preferentially, the antenna should be designed for that frequency. It will then be narrower. Reception of other channels will be poorer.Another calculator for comparison:https://www.changpuak.ch/electronics/yagi_uda_antenna_DL6WU.phpAre all stations pointing in the same direction? If not, the antenna's directional characteristics can help prevent reception from being too strong.

author: CaptDon
author_rank: Super Contributor
timestamp: May 29, 2025, 02:07:16 am
content: All of the broadcast antennas are on the same hilltop and the same magnetic angle from my home. Although their channel numbers are far apart their 'RF frequency' is very close together.