23cm antenna?

Equipment Antennas
61

Hi Elliott,

Yep similar idea to my own thoughts for my 13 cms yagi.

Being 130mm (13cms) the standard 50mm water pipe will do the job nicely (as long as there is no metal compounds within the plastic make-up - a quick check in the microwave oven to see if it gets warm?). A 1/2 wave is about 65mm so unlike your own I will drill holes through centre of the pipe to take each ‘2mm solid rod’ element within itself. Likewise with the driven section - like yours a folded dipole with access holes on either side of the pipe to get access to terminate and mount a BNC or similar.

Now as the tube is 50mm there will only be about ( 65 - 50 = 15mm/2) about 7.5mm protruding - about a 1/3rd of an inch in old money - on either side of the tube. And ideal for clipping onto the outside of my SOTA rucksack without bending the elements.

Locating the yagi on my SOTA pole is determined by drilling two holes using a cone cutter on either side of the tube. The upper side of the pipe has a smaller hole than the lower. This is to accommodate the tapering nature of the telescoping pole. Another set of holes are drilled at 90 degrees. Either set of holes accommodate for vertical or horizontal polarisation operation. The yagi finds it’s own height on the pole (of course I have predetermined this from the hole diameters). I have used this trick from my telescoping 6M to 70cms SOTA dipole which I have used for many years.

Total price to produce the yagi I reckon a tenner £10 - if that. I have all the parts in my workshop bar the 50mm pipe.

Interesting times - on new band for me.

Es 73

Jack(;>J

62

Love it, Jack. And can be scaled for other bands.

EL

63

Of course Elliot,

13cms is ideal for this type of design and likewise 23cms, but as you progress down in frequency you introduce the ‘droop’ factor. Now this not a symptom of old age - just gravity playing with our designs & ‘desires’ :wink: .

Cheers

Jack(;>J

64

I’m also using the SG Lab transverter for 23cm and 13cm and have enjoyed a few contacts on 23cm SOTA so far. The 13cm kit appears to be working but cannot test locally due to lack of stations on that band, hoping for a SOTA contact on my next trip in UK and Ireland.

I will be over in Ireland from 30/03 till 02/04 and EI/IE-003 Tonelagee in the Wicklow Mountains is on the agenda, WX permitting. From IE-003 (817m) there is a good chance to work Wales and the Lake District even with 1W.

I am using home built Yagis: a 10 el. (extension to 21 el.) for 23cm and a 27 el. for 13cm. All aluminium with folded dipole and 4:1 coax balun.

I’ve made an antenna support in polyethylene which clips onto a fiber mast. I would normally use horizontal polarisation for SSB but can easily arrange the clip for vertical polarisation.

Will be posting an alert nearer to the date.

73, Phil ON4TA

ON-001_13cm.jpg1024×754 222 KB

65

Are you going to QRV on April 2nd? I am at the GMDX convention on April 1st so cannot get out to a summit then and I’ll be stuck at work the days before.

66

Anybody using a Quaggi? I have one for 70cm that is very good. Easy to tune and match.
http://n6nb.com/quagi.htm

67

Hi Phil,

Well done on your H/B yagi. Looks very impressive. Presume you used a beacon to determine it’s performance?

And. Interesting feed arrangement which I would possibly like to copy because the folded section could possibly fit within the diameter of the 50mm tube - the folded element through a 2mm hole near the top & bottom determined by the fold spacing - this would make for easy termination. And did you make the balun yourself?

73

Jack(;>J

68

I will be on VHF/UHF from the Wicklow Mountains on March 30+31 and April 1+2, pointing the Yagi across the Irish Sea. Aiming to be QRV around lunchtime, will decide the day before which SOTA to activate as very WX dependent.

I have enjoyed building the Yagi for my first attempt at 23cm (and 13cm). The boom is 15x15mm and has been reclaimed from a 2m Yagi. There is an extra 15cm behind the reflector so I can mount the antenna before-the-mast for local experiments, for SOTA I use a polyethylene support 15x15cm centrally mounted for balance. The boom is drilled for H or V mounting (M6 bolt and wing nut; for when hands are getting cold and wet on SOTA). The support has 25mm plastic clips to click the antenna onto the fiber mast. For safety I add a quick release tie-wrap as high winds have un-clicked the antenna on occasion!

My first antenna for 23cm was a 10 element Yagi, I have since added an experimental “extension” to make it 21 elements. The two sections strap to my rucksack, they are assembled with an M6 bolt. I used a beacon some 85km away to get a feel of the antenna pattern, turning the Yagi by hand as I would do on SOTA. Last year I managed a QSO Ireland-to-Wales with just the 10 el. Yagi but I am very keen to try the full length version this year.

The folded dipole is made from 3.2mm welding rod, it is very sturdy. The 4:1 impedance transformer is made from 50 Ohm semi-rigid coax, attaching it is quite tricky as the center conductor is very thin. A simple jig made from wood off-cuts is a great help to keep the balun in place whilst soldering!

I’d be happy to supply dimensions and some photo’s of the build please send me a PM (email info on QRZ) or I can publish the dimensions in this thread if you feel that is OK.

Photo below of the 23cm Yagi being tested.

73, Phil

SOTA_23cm_21el_Yagi_test.jpg1024×1069 209 KB

1 Like
69

Tks for the reply Phil,

I’ll get back to you direct by email.

Jack(;>J

70

Hi Phil

Publishing the details here would be on topic, and I’d very much like to see them! :smile:

73
Adrian

71

Here are the dimensions of the 23cm Yagi I built. I had a JPG prepared for an article I was working on, it may not scale 100 percent on screen please download the file and print it.

Some (calculated) figures:

10 el. 3dB bandwidth = 41 degrees, gain = 11.7dBd
21 el. 3dB bandwidth = 27 degrees, gain = 15.4 dBd

The elements are aluminium rod 4.0mm, construction method is elements bonded through the boom (15x15x1.5mm). Element lengths are valid for 15mm boom (correction factor applied).

The folded dipole is (welding) rod 3.2mm, construction is 25mm bend (inner) diameter and mounted fully insulated from the boom. Dipole center gap is 5mm.

For transport I made the boom in two sections, a round tube fits inside for quick alignment and two M6 bolts will temporarily fix the two sections.

This design allows to cut the antenna virtually anywhere past the 10th element, say you had a 1m boom available that would be long enough to make a 15 el. Yagi. It is all part of the experiment.

73, Phil ON4TA

Yagi_23cm_21el.jpg417×1346 92.1 KB

1 Like
72

I still haven’t completed an antenna, but I did take the transverter and 817 out onto Long Mynd G/WB-005 for the UKAC last night.

Using the PCB patch antenna, I worked 34 stations in 8 QRA locator squares in an hour and a half, which was much better than I hoped. EDIT: ODX 196km

It was a warm summer evening, and expecting the summit to be busy, I took the heavy tripod etc to set up away from the paths. In the event, I only saw two or three people pass by, and so I used the trig point.

I worked every station that I could hear, and in some ways my broad beam-width antenna was well suited to the task. I’m looking forward to trying something with a bit more gain, though.

What I carried up (except the concrete bit) :

What I used:

I recognised a few SOTAist callsigns, notably Stuart G0LGS/P close to Cleeve Hill, but no S2S on this occasion.

Thanks for all the contacts,

73
Adrian
G4AZS

5 Likes
73

Here is another option I found lurking in my workshop in a box called radio mics.
A pair of log periodics that happen to work at 23cm as checked out on my 23cm SWR meter. Shown here fitted to an mic stand.
I’ll try them out on my next outing

Compton

1 Like
74

I have opted for the 13 element from here : http://www.antennas-amplifiers.com/23cm-High-gain-Yagi-1296-MHz

At a reasonable price including shipping, I may buy the 2m/70cm dual band yagi.

As for the 40 meter 3 element beam… it may be a bit too big for the rucksack!

Matt

2 Likes
75

Another month on, and my home brew 23cm yagi has not progressed very far. In my defence, I was distracted by the gift of an old J Beam 15 over 15 (or 16 over 16, depending on which bits you count!).

This I have cleaned up, and tested in last night’s 23cm UKAC from Long Mynd G/WB-005.

It isn’t at first glance the most practical antenna for SOTA, but it is very light, 900mm long, and hangs easily on the back of my rucksack.

Results compared to last month, using the PCB patch antenna, were better with 36 versus 34 QSOs, 9 Locator squares versus 8 and ODX of 240Km versus 198Km. Not a statistically significant comparison of course, because conditions might have been different, and different stations will have been active.
In the context of SOTA (rather than a contest) perhaps not enough of a difference to make it worth the extra weight and mounting requirements?

“Pointy” antennas do have pros and cons. I heard two strong stations in QSO. They had been working (calling CQ) on the same frequency as each other, but it was only after an hour and around 20 QSOs each that they became aware of that, presumably when their beam headings coincided! Having laughed about it, one of them agreed to move up 5KHz.

My ODX contact was with the same station as last time - though he was in a different location. I heard him for the first time late in the contest, and we had an easy exchange both ways, as compared to a bit of a struggle both ways last month.

Here is a photo of my set up, the transverter being mounted above the antenna. Happily the forecast heavy rain and lightning didn’t materialise:

It was good to be chased by Matt G8XYJ, and have a S2S with Frank G3RMD on Cleeve Hill G/CE-001

73
Adrian
G4AZS

3 Likes
76

I would have expected a reasonable length Yagi to be far better than a patch antenna. Seems a bit odd to me.

77

The supplied antenna is a 3 ele Yagi on a PCB rather than a true patch. ISTR a patch would be about 7dBd and a 3ele about 5dBd (not sure about the gain of small Yagi TBH).

I think the claimed gain of the J-Beam is 15dBi or about 13dBd, so it should be a whole S point and “something” better than the PCB antenna. The J-Beam is a skelton slot fed Yagi and I think that gives it much greater bandwidth than the equivalent single Yagi of more elements. Proper antenna people are welcome to correct any mistakes.

1 Like
78

Found this: http://www.batc.org.uk/forum/viewtopic.php?t=1102

It seems to imply that the J beam antenna might be best used as a ladder for mice.

1 Like
79

I had intended to make A/B comparisons, but I got caught up in the excitement of the contest!

It might be that Long Mynd is relatively close to the centres of activity - such that it is possible to hoover up most of the available contacts with either antenna.

The FT817 isn’t ideal as an indicator of relative signal strength, because it has a step-change bar graph display.
I might try something a bit more controlled, using the old FT290 with its little analogue meter, and a nice switched attenuator between the transverter and receiver. That would assume that the transverter is linear, but my attenuator wouldn’t be accurate at 1296MHz.

GB3SE near Stoke is a good steady signal from high points around here.

Also, this is an old antenna, and although I have cleaned and re-mounted all the directors, I was reluctant to disturb the driven element, because the castings are a bit fragile. I have taken a DC resistance measurement, which was very low - suggesting that there is no corrosion in the signal path. Also, the transverter thinks the SWR is OK on a very short feeder.
But, there could be something amiss.

All good fun :smile:

80

Yes, I found that too! Very few other references - I was hoping to find an original drawing / assembly instructions, as I’m not sure that it had been assembled correctly.

The quality is not top notch. Some of the elements appear to be the correct length (compared to their peers), but are not drilled exactly in the centre. They don’t look like replacements.

I think “odd” is a good word to use, but it had to be worth investigating…

In my bottomless junk box I found 26 identical 6BA bolts to replace the corroded ones. I knew they’d come in handy one day :wink: