Issue 35, October 1992 Six News
UKSMG would like to see this work updated for 2005, please contact the
if you are able to volunteer |
Click here for full details of M2 Enterprises series of 6m beams.
Following the discussion on antenna stacking in the last issue
of Six News, we thought it was about time to look at 6m antennas.
For practical reasons this review is limited to antennas that are
available in the UK and to manufacturers of good standing who are
able to provide adequate after sales support.
There are several related issues to consider when choosing an
antenna: electrical performance, boom length, cost, and quality
of manufacture. Very rarely, if ever, do any of us have an
opportunity to select an antenna without entering into a
compromise on one or more of the above points. The fist three are
directly related, as a quick scan of the table will show. With
regard to the latter, there are no concerns with any of the
manufacturers listed so far as we are aware.
It is always very difficult to objectively compare competitive products when undertaking any purchase but, to act as a starting point, we have plotted graphs in Figure 1 of forward gain and boom length on the same axis. This provides a straightforward way of looking at the trade-off of gain versus boom length. To provide a trustworthy reference we have plotted the forward gains of several NBS designs and joined them together as a reference. Although it is possible to better the NBS design profile, a manufacturer is unlikely to do so by several dBs for a similar length! Which brings us to the most contentious issue, can the gain figures claimed by manufacturers be trusted? First of all, at least one specifies their gain in dBi (i.e. the gain compared to an isotropic radiator). Using this method, manufacturers can seemingly ‘obtain’ an extra 2.1 dB. The standard way of quoting gain is dBd where the gain is relative to a dipole. In my view a manufacturer claiming in dBi does lose credibility and has a ring of specification enhancement to trap the unwary. There is nothing actually wrong with using dBi as long as the manufacturer states so clearly in the specification. Tonna does this, so to enable comparison with other antennas we have taken 2.1dB off the gain claimed. Two other manufacturers seem to claim unusually high forward gains; Create and Cushcraft. Create only state their gains in dB, not dBi or dBd. Looking at the gains claimed by Create in comparison to NBS designs, we take the view that they are really using dBi and we have therefor subtracted 2.1dB from their figures. Cushcraft actually state their gains are dBd however, all of their antennas claim gains greater than NBS designs. For example, their excellent 6m Boomer is claimed to have a forward gain of 14dBd on a boom length of 34 feet. While their competitor, KLM, with a the 6M-14 requires a boom length of 61 feet to achieve the same gain! I leave it to your discretion to decide which is correct! We have split the graph into three sections: economy, serious, and the seriously rich! Here are our recommendations. Remember, choose the best and the biggest antenna you can afford and fit into your garden - you cannot make up for low gain in your antenna no matter how much you spend on your transceiver and mast head amplifier!
If
you are using MS Explorer 3.0 and would like a copy of the table
below in Excel (.XLS) format click here
(select 'open' not 'save'!)
 |
A Tabular Comparison of Commercial 6m Antennas |
 |
Plot of Antenna Forward Gain versus Boom Length |
We really cannot recommend the Jaybeam 4- element, although it is a well built antenna and will last a lifetime, its performance figures are just not good enough for the 1990s. Why don’t Jaybeam pull their fingers out and update the design with dates from the 60s. The best buy in the category are undoubtedly seems to be Tonna and DeeComm. They have sensible prices, are well specified and are well manufactured. In fact DeeComm will manufacture a Yagi to your specification if you so wish.
There is much of a muchness in this category, but we reckon in terms of value for money, performance and cost, Create comes out ahead. Also, look at the weights, compared to some Create are very light. This is an important consideration if you are intending to stack.
What is there to say? In this category cost is of no consequence and there is no problem in having an antenna longer than the mast is high in the grounds of your country mansion. Therefore, the KLM 6M-14 wins hands down, But don’t all rush at once with your cheques for 499 pounds!
To return to the archive page click here