Help with M2 23CM35 yagi

[VK2GOM]

Great idea Doug on the tunable screws, I like that.

I gave up on my 16ele 23cm Yagi. Could just not get it below 3:1.

I will be building another soon; 40ele this time, with a slimmer (16mm square) boom, and with a commercial 23cm driven element, but might install tuning screws like that on the first couple of directors. +/- 10mm adjustment would be ideal.

73 - Rob VK2GOM / GW0MOH

[VK3BJM]

Adam,

If you want a quick way to change the spacing between the driven and D1, try removing the driven and reinstalling with the sealing cap to the front instead of the rear. I note the M2 instructions stipulate mounting driven as you have done, and as shown in your photos. But as it doesn't work quite as it should when installed as per the manual - well, what have you got to lose? Quicker and easier than bending elements and cutting and installing a new D1 - especially without spare retainers...

And it would be interesting to document what happens.

73,
Barry
VK3BJM

[VK4GHZ]

M2 were kind enough to look into this issue, and is presented below so that others may benefit.

Hello Adam,

I had Mike look into this first thing this morning. He spent about an hour or so working on this, actually setting one up on the test stand.

A few things might be happening here.
First, there may be a problem with the driven element.
To eliminate that, we put a new, off the shelf DE on the test antenna.
Verifying that the elements and spacing were at “stock” dimensions, we tuned this for better than 20 dB return loss (equivalent to about 1.2 VSWR) across most of the band, particularly up at 1296.

The next thing to look at is the director length.
One can simulate shortening and lengthening an element without actually changing it.
We use a small piece of tubing, about 5-10mm long, with a diameter slightly large than the element diameter.
Sliding one on each side of the element, one can simulate shortening the element by running the “cheater” all the way in against the boom.
Placing the “cheater” on the tips effectively lengthens the elements. That may lead you to discover if the antenna “likes” an element length change.

One more possibility is the mast used to mount the antenna.
The mast is nearly all cases much run “under” the lip of the “L” bracket and not be run on the other side, allowing it to cross the plane of the elements.
Even a fiberglass mast is “seen” by the antenna and will create a bad match situation.

Another alternative is accuracy of the test gear, including cables.
At 1296, as you may know, it does not take much to be “off,” so sometimes that happens as well. You may have thought of and eliminated that possibility already.

I hope these measures will help get you up and running.
Thank you and 73.

Regards,
Jason Boyer, N6EY
Amateur Marketing and Sales

[VK5PJ]

Hi Adam,
it may be a case that your D.E assembly is just "faulty" or was built out of tolerance, error's do occur with manufacturers and 23cm does not forgive many tolerance errors.

After MANY years of stitting out in the rain, I had poplulated an old 23cm boom with elements about 18 months ago (DL6WU). I have had sleepless nights about how best to feed it and this has always stopped me progressing to be able to use it.

I stumbled over an old DUBUS article by Rainer, DJ9BV (Dubus 2/1994) where he gives details on the construction of various lengths of VERY long 23cm yagi's.

In it they outline the construction of a 4:1 balun out of UT141 on an N socket and a folded dipole out of 4mm copper wire. While I had read it before a few years ago but do not recall what stopped me following his feed system then.

I used a lenght of UT141 instead of the 4mm wire and have just put it out on the test stand an hour ago. The indicated VSWR is 1.2:1 on my REVEX W570 (23cm capable) meter, I have not fiddled it in any way and just did a placement by eye on whether the dipole was central on the boom.

If all else fails, it would be worth a few hours to hunt down the DUBUS article (or I can send the PDF) and you could in an hour or two make a replacement D.E for the M2 yagi.

I know it does not fix what SHOULD work but it might save another sleepless night

Will try to take a photo or two and if your interested I can send them on to you.

Regards,
Peter, vk5pj

[VK3HZ]

I'd thought to mention this too, but not sure if it's much help to you Adam as you probably want the M2 to work with the parts supplied.

I built a long (54-el) DL6WU for 23cm and used the DJ9BV feed: http://www.qsl.net/ok1cdj/dj9bv23.pdf
He had difficulty getting a good match with the standard DE and balun dimensions so altered the lengths to find a good combination.

When I measured the SWR, also using a W570, reflected power indicated zero. I thought the W570 was faulty and turned it around, but still had zero reflected (now indicated as forward) power. So, it was a virtually perfect match. This was with the antenna pointing up vertically with the reflector about a metre off the ground. No change when up the mast.

Regards,
Dave.

[VK2KRR]

Gavin VK3HY.. 1.8:1 at 1296 is not real flash, im sure it would have been better than that when I had it, or else the IC910 would start doing its TX power limiting tricks that it does when it see's a higher SWR. If it seems that far out, I would probably try some of the tricks Adam is working on to try get it better.

[VK4CZ]

Just built a driven element and balun to the DJ9BV specs.... Will be tested soon to compare with the 'standard' DL6WU dimensions!

[VK2FAK]

Hi all...

It seems this return loss issue goes back a long way...I was looking around and found this....it may give some ideas...this from postings on the Amsat site...in 2002...

>I recently installed an M2 23CM35 L-band antenna for use as an uplink on
> AO-40 but am getting a really bizarre SWR curve. At 1250MHz, I get a 1.5:1
> SWR; at 1269MHz, a 2.1:1 SWR and 1.2:1 at 1280MHz (measured with a Diamond
> SX-1000 SWR Meter).

The suggestion was...

"We had a somewhat similar problem on our 432CP30. The
factory suggested we check the resistance to each of the
driven elements to make sure there was less than .1 ohms
between the F connector and the element.

In our case, two of the elements were bad. One had 34 ohms
and the other was something like 4 ohms."


It may be worth having a look into.....

John

[VK4CZ]

My two 1,296MHz 36el DL6WU yagis finally went through SWR testing this afternoon with the help of Kevin VK4UH. (Thank you KJ)

The 'Field Day' version tested 1.1:1.. with fairly flat SWR cure across approx 8MHz. Wow! (fluke??) The second yagi (to be installed permanently here) tested 1.6:1 with the best SWR approx 4MHz low. Swapped in the DJ9BV driven element I build this morning to the second yagi and SWR 1.2:1 with fairly flat SWR curve.

Both yagis have now had the feed points epoxied. Now awaiting next stage on tower refurb here so 2m, 70cm and 23cm yagis can be mounted.

[VK6OX]

Just built a driven element and balun to the DJ9BV specs.... Will be tested soon to compare with the 'standard' DL6WU dimensions!

ImageUploadedByTapatalk1358642284.534970.jpg

A very nice piece of fabrication Scott...well done!! I don't want to take this thread OT so I'll PM you.

Cheers

[VK4EA]

Scott,
What material did you use for the folded dipole?



Sent from my MZ601 using Tapatalk HD

[VK4GHZ]

Scott,
What material did you use for the folded dipole?

I was wondering that myself.
As a last resort, I'd knock one of these up myself.
And to add to Peter's question, where did you get the material, and what was your reference material for dimensions etc?

[VK3QI]

Reference the DJ9BV design.

A link to the article is: http://www.qsl.net/ok1cdj/dj9bv23.pdf

There are quite a few of these antennas floating around in VK3 using this design. Most have been constructed using brass rod for the elements and UT141 hardline for the 4:1 balun, but I have seen a few using copper tube (such as brake line available from REPCO) for the driven element.

The secret for success seems to be positioning of the N socket in relation to the driven element using a suitable bracket, usually at about 45 degrees to enable the connecting cable to clear the elements without having a proximity effect on the reflector or first director.

Our Field Day station VK3ER/p used such an antenna for a number of years with good success before moving on to dualband parabolic setups.

Cheers

Peter VK3QI

[VK4CZ]

Driven element was 3.2mm brass rod. (BTW parasitic elements are 3mm al rod).

The DE on yagi #1 was straight off the DL6WU design as output by the yagi prog by VK5DJ. It tuned 'perfectly'. (still consider that a fluke). The second yagi originally was using the DL6WU, but the DJ9BV was made just in case based on previous comments in this thread. And was used!

After looking at the DJ9BV article, I had to adjust the dimensions to suit my construct... DJ9BV used 15mm boom, mine 19.05mm. DJ9BV not insulated DE, mine fully insulated.

But in essence the main changes I noted after recalculating the dimensions were the 'off centre' gap in the dipole, and the shorter balun.

I also saw articles which described making a 'jig' for bending the DE, which I didn't. I made a number of elements without one and used those closest to 'spec' (<1mm tolerance). A jig would be necessary if making more than a couple, without wastage!

I've taken a number of photos of the build along the way, might have to write it up for a forum topic

And may just have to make a 3rd one so I can install a stack here at home!

[VK3BJM]

And may just have to make a 3rd one so I can install a stack here at home!

Nothing works like an array of four, Scott...

http://www.flickr.com/photos/72319077@N ... 461538031/

http://www.flickr.com/photos/72319077@N ... 461538031/

73,
Barry
VK3BJM

[VK4CZ]

Too true Barry... but may have to wait until I can justify another tower.

I had wanted to do some 432 EME, but realised that unless I rationalise the current antenna array, that an additional tower would be needed to do that properly. As three towers already call this place 'home', I am struggling justifying a fourth!

[VK4GHZ]

Getting the M2 retainer clips off, and being able to re-use them is not that difficult.

Using a small flatblade screwdriver, carefully bend back, only enough, each tab.



You may not have to loosen all the tabs, just enough so that the retainer clip is no longer binding to the element.

Using the same screwdriver, you can start to move the retainer up.
Then using small pliers, you can lift it off.
For longer elements you can use your fingers once there it clears the insulator.



To re-use the retainer, I used a nail punch to gently press each tab back down.
I would expect the tabs to fatigue at some stage, if this process was done repeatedly.

Obviously, you only need remove the retainer from one side in order to pull the element out.

[VK2FAK]

Hi all...

Is the plan still to work out what is wrong with the antenna, or to just get it operating.......the 2 maybe different things...
This problem seems to have been around a while would be interesting to find out what it is...

John

[VK4CRO]

Hi , I have 4 9el 2m M2 yagi and no problems and was thinking of 2 by 35 elements for 1296
But did you resolve the swr problem??
regards Ron

[VK4GHZ]

...was thinking of 2 by 35 elements for 1296
But did you resolve the swr problem??

Hi Ron

Have been a bit busy of late, and put this on the back burner.
If/when it stops raining (hopefully tomorrow), I will sweep the return loss with a network analyzer.
(Rather than measuring SWR with a dubious ham quality SWR meter.)
Can't take the gear out in the rain/drizzle though.

I will certainly post the results here.
As I want to eventually run a bay of four, I am hoping this issue can be resolved before I spend $$$$ on three more.