GH*n3(jed mods)


*NOTE*

The primary purpose of the dimensions below is to upgrade your existing JED build to a UHF/VHF-hi combo antenna. If you do not have an existing JED UHF build use one of my original modular or non-modular UHF/VHF-hi combo models

The antennas below are of Gray Hoverman type. They are mods of the JED's antennas. This means that if you have built one of those antennas you can just add the elements described below and turn your antenna from UHF only into a good UHF/VHF-hi combo. Of course you can build the combo antenna from scratch - in such cases use the corresponding dimensions from the JED's site and this page.

One can find a lot of information about the terminology in the digitalhome.ca's antenna research and development forum.

Below are the net gain and the swr graphs of the combo antennas. The UHF gains are a bit lower than those of the original antennas.

Graph of Net Gain and SWR

It is visible that the VHF-hi performance is similar between GH4n3, GH6n3 and GH6n3, and it is a bit lower for GH10n3.


Modification

The mod that transforms a JED's antenna into UHF/VHF-hi combo is shown on the following picture

jeds to combo transformation diagram

Mod steps

In the plane of the JED's antenna driven elements (in blue) two more elements are added. They are called NARODS, have a hat-like shape and are drawn in black. The NARODS have no electrical connection to the driven elements.

Behind the reflectors of the JED's antenna (in green) a second plane of 3 reflectors is added. Those new reflectors are called narod reflectors and are drawn in red.

The combo antenna will probably require a commercial balun that has low loss in both UHF and VHF-hi ranges.


Dimensions

The distance between the driven elements (in blue) and the NAROD reflectors(in red above) will be denoted X.

s is the distance (center to center) between the horizontal stubs of the NARODs and the driven elements.

The b dimension from the JED's models is also the length of the horizontal stubs of the NARODs.

L1 and L2 are the lengths of the narod reflectors, Z is the distance between them.

h and a are the height and the "head" size of the hat-like NAROD.

dimensions diagram

GH10n3 GH8n3 GH6n3 GH4n3
Dim mm inch mm inch mm inch mm inch
s121/2121/2121/2121/2
a42716 13/1642816 7/839915 13/1640516
h491 15/16481 7/8602 3/8572 1/4
L190735 11/1696037 13/1699539 3/1696137 13/16
L280431 11/16813328133281031 15/16
Z36014 3/164331744817 5/847018 1/2
X2409 7/1630011 13/1631412 3/831612 7/16

All Gray-Hoverman designs are covered by GPL v3 or later as stated here.


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Copyright 2010 Nikolay Mladenov.
nikolay dot mladenov at gmail dot com