Category - M0XXT Archive

We continued the prep work for CQWW SSB this weekend and got the 40m VPA (Vertical Parasitic Array), our Caribbean Array, built and tested. It appears to be performing as expected and should improve our rates on 40m significantly. Photo’s coming soon.

Shack Decoration

29th September 2009

With CQWW looming and it becoming certain that we would not be in our new shack in time, we decided that our current temporary shack could do with a clean up and a fresh coat of paint. So over the last weekend we stripped out everything from the shack, painted and cleaned the room then put it all back together again.

Much cleaner now the walls are painted

It’s amazing how much kit we had in there.

We also took the opportunity to get on the roof and do some work on the matching system for our top band dipole.

CQWW International Invitation

21st September 2009

Friends,

The UK Scout Contest Team is putting on a high power Multi-Two station for CQWW from Dorridge (24th / 25th October 2009).

Would you like to operate a mega-station? The station details are genuinely very impressive and would blow away anyone’s capability they might have at home; from full sized 160m dipoles at 70 feet to 3-element arrays on 40m to the USA. Both multi-band stations have an ACOM 2000 fed by either an FT2000 or a K3. We have station filtering to allow simultaneous high powered operation by two stations just feet from each other on adjacent bands and each band will have at least two antennas available. It’s pile-up heaven.

Stub tuning completed

21st September 2009

Finished tuning the stubs filtering system yesterday, they are quite easy to do however i should probably have done this at the main station shack as my own shack is a bit small for hundreds of meters of Coax

Filtering

20th September 2009

Overview

Very early on in the development of the station we realised that filtering was going to be essential to our station, it would be almost impossible to put together a multi transmitter station without adequite filtering. Because our antenna’s are in very close proximity we set about designing a filtering system that would cope with this.

We decided to address the filtering issue in two stages. The first would be through the use of Band Pass Filters on the low power side (between transmitter and amplifier) and the second stage would be coaxial stub filters on the high power side (between aplifier and antennas). One we bagan to research this we realised quite quickly that there is very little practical information available on the real world use of filtering in a M/2 or M/M contest station environment.

Low Power Stage – Band Pass Filters

After quite a bit of searching for a suitable BPF solution it appeared that there were only really two main options for a Multi-2 setup where each station must have switchable filtering for each band, these are either the Dunestar 600 or the I.C.E Band pass filters. Both of these options are quite expensive and didn’t really help with our understanding of filters as they are essentially off the shelf solutions. It then came to our attention that Bob Henderson 5B4AGN had designed a switchable multi band BPF system based on the W3NQN filter design and had produced a number of professional boards & cases for these.

The W3NQN filter design is very widely used as it provides excellent out of band rejection and is quite simple to construct. See below for the schamtic of a W3NQN filter.

What Bob had done is combine the excellent filter design of W3NQN, with a motherboard & daughter board system that allowed filters for all the HF contest bands to be combined together in one box and be easily switched. We purchased two sets of boards and cases along with the various components needed, these filters also incorporate a band decoder and relay drivers, the relay drivers especially would be essential for our plans for the second stage filters. The filters also allow us to automatically bypass the BPF’s if we are using a band where a supported filter does not exists, WARC bands for example. Below is a picture of one of the completed BPF boxes.

Performance and Frequency Response

Performance of the filters is excellent, these had their first real test on SSB Field Day in 2009 and they performed superbly, however due to the close proximity of our antenna’s there were still some problems on the exact harmonics, these will be dealt with in the second stage filter system.

I will be posting frequency responses when i am able to, however due to the failure of my VNA i am unable to do this currently. Once the new VNA is completed i will update this article.

SWR Response

SWR Response was measured with an MFJ-260C Dummy Load and where taken using 100W from an FT-2000 on an external SWR Meter

BPF1

	160	80	40	30	20	17	15	12	10	6
Control (no filter in line)	1.05	1.05	1.07	1.09	1.09	1.08	1.09	1.08	1.09	1.1
Pass Through	1.03	1.03	1.05	1.05	1.04	1.05	1.06	1.06	1.07	1.04
160	1.19			N/A		N/A		N/A		N/A
80		1.15		N/A		N/A		N/A		N/A
40			1.14	N/A		N/A		N/A		N/A
20				N/A	1.18	N/A		N/A		N/A
15				N/A		N/A	1.38	N/A		N/A
10				N/A		N/A		N/A	1.3	N/A

BPF2

	160	80	40	30	20	17	15	12	10	6
Control (no filter in line)	1.05	1.05	1.07	1.09	1.09	1.08	1.09	1.08	1.09	1.1
Pass Through	1.06	1.05	1.06	1.08	1.07	1.08	1.08	1.06	1.05	1.19
160	1.13			N/A		N/A		N/A		N/A
80		1.1		N/A		N/A		N/A		N/A
40			1.08	N/A		N/A		N/A		N/A
20				N/A	1.14	N/A		N/A		N/A
15				N/A		N/A	1.2	N/A		N/A
10				N/A		N/A		N/A	1.4	N/A

High Power Stage – Coax Stub Filters

Coaxial stubs are very versatile things, they have many uses from antenna matching to phasing lines for antenna array’s, however they are also extremely effective for filtering of harmonics. They are widely used but there seems to be little practical information on constructing a stub filtering system.

There are many different types of stubs that can be used for filtering however we will only be using 1/4 wavelength shorted stubs and 1/2 wavelength open stubs. A 1/2 wavelength open stub, that is a stub that is open circuit at one end will null harmonics on F/2, 3F/2 & 5F/2 where F is the frequency for which the stub is 1/2 wavelength. A 1/4 wavelength shorted stub, that is a stub that is a short circuit at one end will null harmonics on 2F, 4F, 6F… where F is the frequency for which the stub is 1/4 wavelength.

The type of coax to use for stubs is not particularly important, however i would suggest using RG-213 or better (avoid RG-58 if you are using any power at all). The impedance of the stub coax is also not important, for our stubs we use 75Ohm coax. The one factor that will affect the performance of the stubs is the loss of the coax, the lower the loss the sharper and narrower the null, coax with higher losses will present a shallower but wider null.

When building stubs, it is useful but not essential to know the velocity factor of the coax being used as this will allow the rough cutting of the coax to be more accurate. Stubs cannot be cut by measuring only, it is essential to use some form of analyser to tune the stubs correctly. I would advise that any stubs be rough cut with sufficient spare left for the final tuning. Stubs should also be well insulated at their ends as high voltages can be produced here.

Single stubs can be very effective, however they often leave harmonics outside of their null’s, because of this our filtering system was designed to utilise multiple stubs on each band to reduce the harmonics as much as possible. As the null’s can be quite sharp they will often not cover enough of the band, to address this two stubs for the same band can be connected together, this will provide much greater attenuation, however if the tuning of the stubs is offset then this will also widen the null to the extent that it will cover a sufficient partion of the band.

There are many ways of switching stubs, however we decided that we would utilise two ArraySolutions SixPak switches for this purpose as this would allow us to switch in feed lines with our multi stub arrangement attached for each band, it would also allow us to share the one stub system between the two operating positions.

The SixPak’s have been modified to take some nice lockable DIN connectors, this allows us to easily dismantle and re-assemble the system as needed, it also makes things a lot easier to fault find if a piece of equipment needs to be removed. The two SixPak’s are driven by the band pass filters which contain current sourcing relay drivers, these are connected to the two SixPak’s via an interface box that allows us to drive the two SixPak’s in tandem. The Stub’s are then connected to between what would normally be the antenna outputs.

160m Stub Arrangement

160m uses a simple two stub arrangement, these are 1/4 wave length on 160m

Center of nulls

Cable	160m	80m	40m	20m	15m	10m
HPF160S1A		3.510	7.035	14.095	21.155	28.230
HPF160S1B		3.550	7.105	14.210	21.315	28.478

HPF160CC is the phasing line between the two sets of stubs and is cut to 1/24 wavelength at 1.900Mhz

80m Stub Arrangement

80m uses a simple two stub arrangement, these are 1/4 wave length on 80m

Center of nulls

Cable	160m	80m	40m	20m	15m	10m
HPF80S1A			7.044	14.093	21.160	28.244
HPF80S1B			7.108	14.223	21.300	28.550

HPF80CC is the phasing line between the two sets of stubs and is cut to 1/32 wavelength at 3.550Mhz

40m Stub Arrangement

40m uses a six stub arrangement, HPF40S1A & HPF40S1B are both 1/4 wavelength shorted stubs which will null 20m & 10m, however this still leaves a harmonic on 15m to deal with. This is addressed with stubs HPF40S2A & HPF40S2B, these are both 1/4 wavelength at 10.5Mhz or 1/6 wavelength shorted on 40m, however this presents a problem as it will affect the SWR on 40m. To compensate for this stubs HPF40S3A & HPF40S3B are inserted in parallel as compensation stubs, these are both 1/12 wavelength on 40m.

Cable	160m	80m	40m	20m	15m	10m
HPF40S1A				14.090		28.238
HPF40S1B				14.245		28.560
HPF40S2A					21.220
HPF40S2B					21.350
HPF40S3A					21.220
HPF40S3B					21.350

HPF40CC is the phasing line between the two sets of stubs and is cut to 1/16 wavelength at 7.100Mhz

20m Stub Arrangement

20m uses a four stub arrangement, these are 1/4 wave length on 20m, two are shorted and two are open

Center of nulls

Cable	160m	80m	40m	20m	15m	10m
HPF20S1A			7.044		21.160
HPF20S1B			7.110		21.400
HPF20S2A						28.263
HPF20S2B						28.580

HPF20CC is the phasing line between the two sets of stubs and is cut to 1/24 wavelength at 14.225Mhz

15m Stub Arrangement

15m uses a simple two stub arrangement, these are 1/4 wave length on 15m

Center of nulls

Cable	160m	80m	40m	20m	15m	10m
HPF15S1A				14.090		28.230
HPF15S1B				14.245		28.560

HPF15CC is the phasing line between the two sets of stubs and is cut to 1/24 wavelength at 21.300Mhz

10m Stub Arrangement

10m uses a four stub arrangement, two are 1/2 wavelength on 10m, the second two are 1 wavelength on 10m or 1/4 wavelength on 40m

Center of nulls

Cable	160m	80m	40m	20m	15m	10m
HPF10S1A				14.090
HPF10S1B				14.230
HPF10S2A			7.058		21.215
HPF10S2A			7.110		21.375

HPF10CC is the phasing line between the two sets of stubs and is cut to 1/6 wavelength at 28.500Mhz

SSB Field Day 2009

18th September 2009

Field days seem to whoosh by in a seamless tirade of bodily abuse that starts in the balls of the feet, grows through your hands and wind blown cheeks before reminding you that you are starving hungry and you’ve only just taken over the driving seat.

A very dissapointed 1012s QSO this year and we still can’t work out why we lost ground so fast with the other leading stations, even on 80m where we should have held our own. Certainly having a tribander at only 35 feet is a hell of a penalty to have to suffer every year, but why our 40m and 80m runs were not producing the numbers that the other high-flying entrants were managing? I just don’t know. High probably does mean might. Last year’s 1,000 foot entry was very different on the higher bands to this year. Mostly, we were firing right through a heavy forest. I wonder how much attenuation there is in 500 yards of dense oak trees that are about 80 feet tall? Well, you get my drift.

Filtering this year was amazing. We used a second rig as a dedicated 2nd receiver using James’s new Band Pass Filters, made to Bob Henderson’s designs and we had negligable breakthrough. I can’t wait to use the new permanent multi-two station when we have the stub filters in place too.

Dorridge Day 2009

18th September 2009

Fan Dipoles at 50 feet, 400 watts and lots of atmosphere. We scored just under 100 contacts mostly UK based throughout the UK.

After bumping into my friend Alan (G3LUA) on 80m, he jumped in his car and came to see us with his wife. Alan was one of my instructors at Solihull Amateur Radio Society when I first applied for a license and realised that I couldn’t do the RAE anymore, I had to do a Foundation exam. I did finally achieve my aim though, I took the last ever RAE ever held in Dec 2004 (I think). and passed..!

Lovely day, great fun and good excuse to roll out the toys again.

Wendy and her team were also out in force with Girl Guiding. Having both Guiding AND Scouting in the one family can be hilariously funny as we compete with each other. I won the tallest structure, she won the most colourful!

Pictured is James (2E0YOM) running the pile on 80m.
Callum.

The Station

17th September 2009

The M0XXT Contest station is located in the Dorridge scout hut.

We are currently undergoing a shack move and major station re-design, below is the current systems overview schematic for the planned station

we will be documenting the various elements of the new station as it is designed and constructed, so check back often for updates.

Great Circle Map Centered on the M0XXT shack

Band Pass Filters Complete

17th September 2009