Tuesday, 18 September 2018

DCI-145-2H 2m Filter.

I recently swapped an unwanted Daiwa VSWR meter for a DCI-145-2H 4 pole bandpass filter for 2 metres.   I don't really need it however I have on the odd occasion thought it might help with some strong out of band signals that occasionally pop up so swapping an unwanted piece of equipment for a piece that might be useful I thought was a good deal.

DCI quote the following specification.

Centre Frequency : 145MHz
Band Width : 2MHz
SWR : < 1.3:1
Return Loss : >18dB

DCI measure the filter response at the following intervals.

135 MHz : -72.650 dB
140 MHz : -46.450 dB
145 MHz : -0.755   dB
150 MHz : -42.981 dB
155 MHz : -65.548 dB

Out of pure interest I thought I see what I measured the above as using the DG8SAQ VNWA.

Filter response etc measured with the VNWA.
As you can see the filter specifications for SWR, RL as described the only difference is with the filter skirt readings being slightly off but in quite good agreement with DCI which I'll assume used a slightly better VNA than the one I have. ;-)

Saturday, 8 September 2018

New 2m Antenna Is Finally Installed.

With the help of my nephew Fred and Dave M1DNJ I've finally got the two new Powabeam 9 ele CQM's installed, see my previous post for specifications.

Fred got the job of taking down the original system which consisted of a single 9 ele LFA from InnoAntenna this antenna has worked faultlessly and in fact I only switched to the CQM design due to weight, I don't have a tilt over mast so the stub needs to be lifted into place with the top beam as well as the coupler and 70cm beam by hand not a easy task while standing on a ladder, the LFA even survived being dropped into a hedge from 8m with the rotator and mast attached when the guys from MM0CUG took the antenna down before fitting it to the new mast.

The original 2m LFA with a 70cm 12 ele above.
The first thing to do was remove the original antennas Fred duly got on the steps and disconnected the antenna tails and loosened the rotator stub clamps.

Fred disconnecting feeder and loosening clamps
With antenna removed Fred G-Clamped the new rotator cage to the garden bench and fitted the rotator and thrust bearing which we both proceeded to align. 

Rotator, Thrust Bearing Fitted and Aligned. 
With the rotator and bearing completed Fred got on with the task of fitting all 18 parasitic elements as well as the driven elements to the booms ready for installation.

Fred with set square fitting the parasitics.

Dave M1DNJ and Fred along with Amber then got on with fitting the rotator cage including stub mast, top beam, power coupler and 70cm to the mast thank the gods Fred has good arm strength and a taste of heights.

Stub with top beam, 70cm beam and cage fitted.
Next up was fitting the bottom beam to the mast. 

Bottom beam being attached to stub.
And finally connecting up the bottom beam to the coupler and jobs a good un. 

Coupler connections all done.
And lastly fixing the cables to the mast.

All most done.
Hurrah the finished system finally raised.

The new system raised.
The system gives an VSWR of 1.1:1 @ 144.300MHz with a resistance of 45ohms and reactance of 2 ohms.  

I must give thanks to Dave M1DNJ, Fred and Amber putting up with me trying to run them over with the wheelchair while I fretted over various bits and pieces.   I've been told I'm quite OCD about my antennas. ;-))

UPDATE : 6th September 2018 --   Well the first hard rain since putting the antenna up and the SWR has shot up to 6:1 oh bother this means sadly I'll be off 2m for awhile until I can get the antennas down and workout where the water has got, I suspect the Powabeam driven element ABS moulded fixing block which I had heard can give issues I thought I had sealed it up with extra sealant but obviously not!