Help with M2 23CM35 yagi

[VK4GHZ]

Hi all

Just wondering if anyone else has an M2 23CM35 yagi?

The 23CM35 instructions suggest leaning the DE forward.
I have done that (see image below) and the best match I can achieve @ 1296 MHz is not wonderful at 1.8:1.
It is an improvement over the initial 3.5:1.



Rated 1250 - 1300 MHz, there are many troughs in the SWR curve.
My best match 1.2:1 is down at 1263 MHz.

The best match at 1296 I can achieve is 1.8:1.
I'm not entirely happy with that.
Tests being done with a 1300 MHz rated SWR meter, and the yagi is 7 foot above ground.
I am normally standing on a ladder from behind the reflector when tweaking.

What have you done to improve the match at 1296 Mhz?
Help!

I have noted the following;



When I place my fingers across here (note where index finger is), the match @ 1296 becomes 1.2:1.
Can hardly operate like this though.

Also, placing a finger towards the end of D2 has a large (bad) effect on the match, more so than D1.
I wonder if D2 is too long.

Any suggestions welcome.
(And yes I have contacted M2 several days ago - and no, they have not replied).

Very frustrating, and holding up putting up the new 2m stack.

[VK4WDM]

You could have at least painted your fingernails for the photo

If "body capacity" is changing the impedence of the feed something must be wrong somewhere. I would have a very careful look at any metal to metal contacts and make sure that there is no s--- on them.

This sort of thing can be very frustrating, especially at a frequency where just breathing on something can change it.

73

Wayne VK4WDM

[VK3PF]

Adam,

I have no experience with the M2 antennas. Given that tilting the DE forward helped, you could try bending Dir1 back (or forward), a little at a time. I would bend it a small amount on both sides and see the result - if it goes the wrong way, rotate the element 180 degrees so that it now bends away from the DE. From memory, the DE-D1 spacing has significant effects on the feed impedance.

Good luck,

Peter VK3PF

[VK3OE]

Hello Adam,

I also have the same M^2 23 cm antenna. I followed the instructions very carefully, even brought a micrometer to measure the elements to be sure that they were all in the right place.

I used a calibrated length of 50 ohm cable with a HP network analyser. I bent the DE forward and back. Result = 1.8 to 1 at 1296, exactly as you describe.
I used the finger test but with nail polish and I got the SWR to 1.0000:1, well just dreaming.

So, it seems to be a genreic problem with these antennas, the claim of SWR of 1.2:1 typical over the frequency range 1250-1300 MHz is clearly misleading.
Maybe they should have said SWR < 1.8:1 over the frequency range 1350-1300 MHz as that is what it seems to really be.

Maybe they can send you the optional finger and thumb.

73,

Andrew
VK3OE/VK3OER

[VK2GOM]

I have just been playing with a home built 23cm Yagi this evening... can't get better than 3:1 Lots of 1st director and DE tweaking and bending too.

I even have a commercial Wimo driven element from one of their Yagi kits, which I substituted for my home brew one. In free air, the Wimo DE shows 1.5:1, but once in place on the Yagi, it jumps to 3:1.

This will have a bearing on my field day this weekend. I can't see there being any chance of obtaining a commercial 23cm Yagi between now and Saturday morning

73 - Rob VK2GOM / GW0MOH

[VK4GHZ]

Appreciate all the comments so far.

I should have added, I was especially anal in assembling this one!
Using digital calipers to measure element lengths, and for centering to better than 0.5mm.
The assembly manual says "Accuracy of 1/32" is adequate."
(1/32" = 0.8mm)

Before I screwed the DE to the boom, I slowly slid the DE along the boom (whilst observing SWR) and determined that the best SWR was actually forward, towards D1.
Once you bend the DE forward, access to the mounting screw becomes awkward.

Not only that, you will no doubt (sooner or later) break the solder connection under the heatshrink in manipulating the DE.
At this stage the DE will probably have kinks in it from using a wooden dowel etc to bend it forward, and plier marks in trying to squash it towards the boom.



I took the DE off, removed the heat shrink and inspection bung, and carefully straightened each dipole half in the vice.

It seemed better to preset some forward lean using something with a broader face.






Where in Australia can you get these 3/16" stainless "shaft retainers" they use?
(And what's their real name?)

Once the element is fixed from both sides, that's it!
The only way of getting an element out is to nip away at one of the retainers.

If I can get some retainers, I can experiment with adjustable D1 and D2 lengths.
ie; Get some similarly sized rod, cut 10mm shorter than spec, and tapped with an M2.5 hole at both ends.
M2.5 x 12mm bolts would become adjustable 5mm tips.

Considering D2 caused a bigger "spew" in SWR with finger proximity, I'm inclined to experiment with D2 first.

[VK4TI]

Hi all

Just wondering if anyone else has an M2 23CM35 yagi?

The 23CM35 instructions suggest leaning the DE forward.
I have done that (see image below) and the best match I can achieve @ 1296 MHz is not wonderful at 1.8:1.
It is an improvement over the initial 3.5:1.



Rated 1250 - 1300 MHz, there are many troughs in the SWR curve.
My best match 1.2:1 is down at 1263 MHz.

The best match at 1296 I can achieve is 1.8:1.
I'm not entirely happy with that.
Test being done with a 1300 MHz SWR meter, and the yagi is 7 foot above ground.
I am normally standing on a ladder from behind the reflector when tweaking.

What have you done to improve the match at 1296 Mhz.
Help!

I have noted the following;



When I place my fingers across here (note where index finger is), the match @ 1296 becomes 1.2:1.
Can hardly operate like this though.

Also, placing a finger towards the end of D2 has a large (bad) effect on the match, more so than D1.
I wonder if D2 is too long.

Any suggestions welcome.
(And yes I have contacted M2 several days ago - and no, they have not replied).

Very frustrating, and holding up putting up the new 2m stack.

What happens when you tape a thin strip of alloy coke can in the finger test area ?

[VK6ADF]

Where in Australia can you get these 3/16" stainless "shaft retainers" they use?
(And what's their real name?)

A bit of looking on google and I found the clips are called internal tooth springrip retainers.



Now where you get them from, I don't know but any industrial nut,bolt and washer retailer may have them.

An internal tooth lock washer looks similar but not exactly but who knows it might be possible to use for the same job if you find them instead.

[VK2ABO]

G'Day Adam
You may want to try supercheap auto as these type of clips are used in door trims in older cars and other internals. If you can find a motor trimmer they also may them.
Cheers
John

[VK4GHZ]

What happens when you tape a thin strip of alloy coke can in the finger test area ?

Barry, I taped a narrow layer of aluminium kitchen foil near where my index finger was.
(Effectively extending that DE tubing half)
No difference.


But this morning, got a response from M2.

Hello Adam,

I’ve forwarded your email to Mike Staal for assistance.
He’s got a few tricks to make this antenna match pretty much anywhere in the band where you need it.

He’s working on some custom antenna designs, but should get back to you at his first convenience to help you out with this.

Thanks for your patience and 73!

Regards,
Jason Boyer, N6EY
Amateur Marketing and Sales

Will wait and see what they come back with.
VK4OE also has a 23CM35, and has observed the same matching issues.
I think this will help quite a few people.

In the meantime, I think I have one spare retainer here, so I can sacrifice one to get D2 off, and try a shorter element there.

[VK2KRR]

HI Adam

I had one of these before I set up my dish for 1296. They work quite well.

I recall having to move the driven element around quite a bit, but I did eventually get a very good SWR it would have been in the 1.1?:1 area. I am really particular with getting my SWR, Ret Loss very close to perfect on all of my antennas.

Numerous people have PROBLEMS with M2 antennas, mostly with manufacturing and SWR issues. I'd have to say this 23cm yagi is the only antenna i have gotten from them that I didn't find any problems with. Even my marine yagis I got were not built/tuned correctly, it was so bad it was embarrassing. I emailed them and even sent photos and got no response like you. After spending so much money, I exepect not to actually have to modify them myself at all.

In anycase, I sold my 23cm yagi to Gavin VK3HY, I believe he still uses it for field days, it would be interesting to see what SWR he is getting from it now and if he has touched the driven element at all, perhaps a photo of it if its still testing good.

Edit- also try moving the ends (ie the curved ends of the dipole) of the DE closer to D1.

[VK4TI]

What happens when you tape a thin strip of alloy coke can in the finger test area ?

Barry, I taped a narrow layer of aluminium kitchen foil near where my index finger was.
(Effectively extending that DE tubing half)
No difference.


But this morning, got a response from M2.

Hello Adam,

I’ve forwarded your email to Mike Staal for assistance.
He’s got a few tricks to make this antenna match pretty much anywhere in the band where you need it.

He’s working on some custom antenna designs, but should get back to you at his first convenience to help you out with this.

Thanks for your patience and 73!

Regards,
Jason Boyer, N6EY
Amateur Marketing and Sales

Will wait and see what they come back with.
VK4OE also has a 23CM35, and has observed the same matching issues.
I think this will help quite a few people.

In the meantime, I think I have one spare retainer here, so I can sacrifice one to get D2 off, and try a shorter element there.

Obviously you realise mechanically altering the shape , element spacing and the feeder have a major effect , not having bought such an antenna exactly escapes me but I know with mine (home built) I tuned it by altering the spacing some and squashing the feed point a bit and adding some metal with the tig on the balun side of the driven element . Either the plans were imperfect or mechanically I made errors . Perhaps the thing is not to spec and the reply's may confirm this , good luck it as I expected adding metal would alter the resonance and impedance (feeder is flat into a dummy right?) . Those retainers look like furniture retainers used to locate and tighten metal rods , sorry no source though .

[VK2MER]

Hi adam I think u can get tooth clips from rs components

[VK5BC]

Hi Adam

I use a M2 23CM35 yagi and mine tuned perfectly, in fact I thought there was something wrong with the SWR meter, it wasn't moving so put fingers across DE and sure enough up came SWR. I assembled it exactly as per their instructions, one of the hardest tasks getting the correct length elements in correct order. In real life I think it performs better than my previous 1296 yagi, a homebrew 28 el DL6 design.

Incidently I think Mark VK2EMA has a bank 0f 4 and seems to have a lot of success, may be worth asking him.

I have 3 other M2 yagi's, 6M7 & 6M5XHP 6m yagi's and 2M12 2m yagi. Could not get the 2M12 SWR down to what below about 1.5 so emailed to M2 who told me to put it up and it would work, not much assistance, the 7el 6m yagi starts to died just above 50.200 and is my present 6 m antenna, I not sure its as good as my home brew 6 el YU7EF design yagi. Only had the 6M5XHP up for a couple months but SWR was good to about 50.5 and it seemed to perform OK, would make a great portable yagi, quick & easy to assemble.

Will be interesting to see what M2 say.

73's Brian
VK5BC

[VK4AFL]

Hello Adam - Under no circumstances should you try & improve the match of your M2 antenna [or any antenna] by playing with director lengths or spacing. This is introducing another error in an attempt to fix an existing error. These antennas have been critically designed & changing something is guaranteed to have a negative impact on the pattern, gain or f/b etc which defeats the purpose of buying the antenna in the first place. The only exception to this is if the maker supplied you
with an element that was the incorrect length but I think you have already checked that. In the picture the antenna for testing purposes looks very low which might well influence the SWR. Get it up higher & in the clear. It does not take much
capacity loading at 1296 MHz to alter its tuning. Failing that the only thing you can play with are the dimensions of the driven element which usually means making another one but I would be surprised if that turns out to be necessary. Have you tried another feeder line? You were looking for some Heliax at some point contact me if that is still the case.
Regards & 73`s, Trevor, VK4AFL.

[VK3AUU]

I would have to disagree with Trevor. Altering the spacing and/or length of the first director can have a significant effect on the matching and may actually be the solution to your problem. Tie a length of nylon to the ends of the director and pull back toward the DE and observe what happens, that should give you a clue which way you should ulimately bend it. I would not touch the driven element. Also, point the antenna straight up with the reflector half a metre or more above the ground.

David

[VK5PJ]

Hi Adam,
Trevor and David both make very valid points, both of which have caught me out over the years.

Hello Adam - Under no circumstances should you try & improve the match of your M2 antenna [or any antenna] by playing with director lengths or spacing. This is introducing another error in an attempt to fix an existing error.

Failing that the only thing you can play with are the dimensions of the driven element which usually means making another one but I would be surprised if that turns out to be necessary. Have you tried another feeder line? You were looking for some Heliax at some point contact me if that is still the case. Regards & 73`s, Trevor, VK4AFL.

I had spent an entire afternoon trying to get an older design 432MHz yagi from the ARRL to work back in the lat 1980's to only find the length of coax between the yagi and the SWR meter was a bad length. Only after a friend asked me to change the coax did it all start to work and I could get a SWR below 2.5:1 on the T match.

On my current 432 yagi (K1FO experimental 32 element) which has a folded dipole, I had to reduce the length of Director 1 to get the SWR below 1.8:1 so do not exclude these from your investigations. I seem to remember that M2 told Leigh (2KRR) to slide some nuts along Director 1 to see if that improved his SWR problem, I guess making the element FATTER would be the same as making it longer? Maybe Leigh can remember more?

Regards,
Peter, vk5pj

[VK4AFL]

David VK3AUU you did not read my posting correctly! Yes changing the length/spacing of the first director most certainly will affect the matching BUT its not the way to do it because you are creating another error in an attempt to correct an existing one. Sure you might end up with a great match but what has it done to the rest of the parameters? To fix a
problem first you have to establish the source of the problem rather than blindly bending things. 73`s, Trevor, VK4AFL.

[VK4ADC]

I make a point of aiming my yagis straight up into the air when checking/tuning them - that goes for anything from a 10/15/20M tribander up to 23CM+. Just make sure that you have the back of the yagi well above ground - the standard big plastic rubbish bin is a good starting point and it puts the back about 1.2M above the ground - using nylon ropes to hold it vertical.. I find that the SWR across a typical yagi's frequency range is virtually the same as when it is finally mounted at a 'suitable' height.

My homebrew 23cm yagi wasn't producing the lowest of SWR figures at 1296.1 and in the week preceding the 2012 Spring Field Day, I set about optimising it by cutting off about 10mm from the ends of D1 through D3 (6.3mm diameter solid rod), then tapping those ends, finally adding 4mm screws/locknuts. I also ended up adding some brass shim to my brass folded dipole and then soldering it in its final position. I used a remote signal source on 1296 on receive plus a directional coupler on transmit to re-tune these three directors. I got the SWR well down this way but the thing really dropped to 1:1 when I added a rectangular section of 10mm square mesh directly behind (and then nylon-tied) to the reflector. The polar pattern was probably better, only having the major lobe plus some minor ones well down, and that was how I left it for that event plus the 2013 Summer FD this weekend. I am happy with how it works in the field so it will stay that way now.

[VK3HY]

[Quote]

In anycase, I sold my 23cm yagi to Gavin VK3HY, I believe he still uses it for field days, it would be interesting to see what SWR he is getting from it now and if he has touched the driven element at all, perhaps a photo of it if its still has it.

Hi Leigh

As Leigh mentioned, I purchased his 23CM35 Yagi a few years ago. I used it for the FD this weekend and as a solo FD operator find it easier to manage than the 1m dish I had previously used. It seems to have a little more gain too which is a bonus. I had not previously checked the VSWR so having read the previous postings did so today.

1290MHz. 1.8:1
1292MHz. 1.65:1
1294MHZ. 1.5:1
1295MHz. 1.5:1
1295.8MHz. 1.7:1
1296MHz. 1.8:1
1296.5MHz. 2:1

The folded dipole element is bent backwards toward the reflector. This was done (by Leigh, I guess) and I haven't altered it. I will post a picture of the driven element when I figure out how to do that from my iPad or when I return home later in the week.

73 Gavin VK3HY