Wednesday, 18 July 2018

2m Antenna Upgrade.

I current have a single 9 Ele LFA from G0KSC and though I have no complaints regarding the antenna I'm now at a stage where the only place I can make a sensible improvement in my 2m setup is to replace the antenna.  

I would have liked, probably like most amateurs, to have more the space to put in an array of four 9 element antennas however this isn't practical on my property.  

Now I would like to give EME ago at some point but I don't have elevation available so this put me in a quandary how to improve the system why still allowing myself a little bit of freedom to still carry out a few EME and Meteor Scatter communications when conditions allowed but also give me a better score in the RSGB 2m UKAC as well as general tropo, E's etc QSO's.

I had a chat with few local amateurs I discovered one of them M1DNJ has a similar setup to myself but has a better antenna and mast setup after numerous discussions with David I decided I go with a 9 Element G4CQM design made by Powabeam antennas a CQM9C4 as the performance looked to be about the same as the LFA but with the bonus it's lighter in weight so would make lifting on the mast much easier to accomplish as I don't have a tilt over.   I decided to go with a of two stacked Yagi's.

Richard at Powabeam has published the specifications for a single Yagi as well as a quad array but I couldn't find the specifications for a stack of two so decided to run the simulations myself.  I'm not going to go through all the figures and configuration that can be deduced from the Powabeam website and the images below.

4nec2 - 3D - 2 x CQM9C4

Total Field - 2 Stacked CQM9C4
Horizontal Plane - 2 Stacked CQM9C4

Verical Plane - 2 Stacked CQM9C4

TANT - CQM9C4 - 2 x Stacked Array.

Tuesday, 17 July 2018

2m quarter wave coupler

I'm just about to update the 2m antenna system moving from a single 9 element LFA by G0KSC to two 9 element CQM9C4 Powabeams stacked.   To stack the two yagi's you need a coupler to join to the them together.

A quick search on the net I came across two ways of doing this one based on using coax and the other using aluminium box section with a 15mm copper pipe forming a square piece of coax.

You can buy a ready made coupler but I so happened to have a piece of aluminium box section of the correct length as well as a piece of 15mm copper pipe and three N-Type laying around so I though I'd see if I could save myself £70 and build one myself.  

The way to work the dimensions you use a piece of software called appcad this will allow you to calculate the length of the inner copper pipe which turns out to be 520mm for my size of aluminium box I followed the design for the two port coupler from DG7YBN's website.

What I found was the length isn't particularly critical but the distance between the copper tube running thought the box section is my ali box has an inner dimension of 24mm and as mentioned before the copper pipe is 15mm which requires a spacing of 4.5mm to obtain this I wound insulation tape around a screwdriver until it conformed to the 4.5mm and then used this to centralise the tube in the section.  

An afternoon with the hacksaw and drill press I had the basic coupler built and I ten minutes with a 100W soldering iron had the copper tube soldered to the N-Type sockets.

I tested the coupler on the VNA and got a return loss of around 25dB and a VSWR of 1.1:1 which is near enough so I'm a happy bunny.

I'm still awaiting the materials to build the powabeam yagi's but I'll post again with the build and how they went together.

2m Quarter Wave Coupler Results @ 144.3MHz

Sunday, 8 July 2018

Vine 6M4DX

A few weeks ago a message came up on my radio club message board offering a Vine 6M4DX 4 element 6m beam for sale, now I've not worked much on 6m and in truth I don't tend to working on anything other than 2m and 70cm but the antenna was cheap £40 pounds so I emailed the seller Colin and bought the beam.  

Now I wasn't holding out for much as it's a secondhand beam but upon picking the beam up I was pleasantly surprised as the beam came in the original box and been taken down and packed away with the bits marked and fitting placed into plastic bags, happy days.

I thought that the beam was missing any instructions and I was unsure of how to fit the hairpin match so emailed the manufacturer which I discovered had ceased trading in 2016 but there website is still present with an email so I emailed them not expecting a response.    To my utter surprise Ron at the aforementioned company emailed me back with 12 hours with all the specs and fitting instructions  which I thought was amazing and I only wish some companies that are trading could match this defunct companies customer support. 

The Vine 6M4DX has the following radiation pattern. 

6M4DX Radiation Pattern
I also managed to pick up for free an older rotator and controller so this would get me QRV 6m for next to nothing from a friend of mine so even more happy days.

Here's my nephew Fred and my mate Mal G1NOX
baking in the sun putting the beam together. 
It took Fred and Mal about 4 hours to construct the beam and get it up on the chimney.

The completed beam up on the chimney stack

When I tested the VSWR the beam gave less than 1.5:1 across the whole 6m band which is fine for my purposes.  

Now typically once the beam was up the rotator controller died within 5 minutes, oh bother so I need to fix that before I can the beam a full work out.  But all in all a great bit of kit for peanuts and gets me active on 6m.

Iceni 70cm Transverter from G4DDK - Part 4

I finally got around to finishing the Iceni transverter as depicted below.

Finished Iceni Transverter
The unit is configured to give 17dBm for 0dBm of drive which is then reduced a bit more so that the 70cm PA gives 30dBm which is great for the BNOS 432-1-50 PA I have.

All in all a great project which I'm extremely happy with.