Help with M2 23CM35 yagi

[VK4GHZ]

It's nice being able to "see" what's going on now.
This is a R/L sweep of the 23CM35, with the DE returned to the stock standard position.



No wonder it tunes up so well, down on the satellite band.

I found that altering the length of D2 (the element most susceptible to "finger proximity") did not affect the frequency of best match.
Same with D1.
This verifies what the AV-1000 SWR meter was telling me.
Moving some nuts, (as per the M2 advice), along D4 did though.

Having a "better" reflector, some solid aluminium plate, made no difference.

As per the M2 advice, moving the DE close to Reflector lowers the frequency of best match. You reach a point where moving it closer to D1 does nothing, and this is no where near 1296MHz.

If you can imagine it, having two fingers touching the DE, where the DE tubes are welded to the aluminium box, has a huge difference. There is a nice dip in return loss @ 1290 MHz.

M2 actually have a replacement DE in the mail to me.
When it arrives, it will be interesting to see if there is any difference, and whether the original DE was simply "out of spec".

[VK2JDS]

Hi Adam, your comments about 'dubious swr meter' are well founded.
that meter has problems.

i have 2 of the avair av1000 meters that i use for 23cm.
for a correct vswr reading only apply enough power to just get the 'calibrate' (fwd) to full scale with the sensitivity knob flat-out.
then flick to reflected and see what it reads.

both these meters of mine do the same thing : if you run 10 watts the best vswr is nearly 2:1, while running less than half a watt you get to see the true swr of an antenna down to 1.1:1
stray rf leaks inside the instrument is the problem

there is no substitute for proper test gear, like network analysers and bird wattmeters, but they are expensive.
73 from Dave vk2jds

[VK4GHZ]

...both these meters of mine do the same thing : if you run 10 watts the best vswr is nearly 2:1, while running less than half a watt you get to see the true swr of an antenna down to 1.1:1
stray rf leaks inside the instrument is the problem

That's a great tip, Dave.
Thanks for sharing, will have to keep that in mind.

OK, a replacement driven element was received from M2 yesterday.


Above: 23CM35 broad Return Loss sweep with replacement DE.


Above: A closer look at 1240 - 1310 MHz

I noted the small variations in screen shots (after they were taken) due to my own proximity to the rear of the yagi (18-24" away), but essentially the same pattern.

Note; good match down on the satellite band, as well as @ 1296 (R/L = -21dB = better than 1.2:1).
And if you were using these vertically polarised for FM work, the good match @ 1273 as well.
(I don't think that 20 MHz wasteland in between repeater inputs & outputs should bother an FM operator?)

Just like the manufacturer intended.

Not only that, this is with the DE mounted in exactly the prescribed spot.
ie; it is not leaning forward or back, nor was the height above boom tweaked at all... it was just bolted on.

The original DE must have been out of tolerance.

I'd like to thank both Jason and Mike at M2 for great service.

[VK4CZ]

Great news Adam.

[VK2JDS]

indeed great news, but i must ask, what can you see as a difference between the 2 driven elements?

the plots look great for the new replacement one!

on a sidenote, check http://vk1od.net/transmissionline/VSWR/vmhsl.htm
it describes problems with cheapy swr meters that use 1n4148's as detector diodes.
so, we have internal leakage and non linearity in detection to contend with when using these types of instruments

73 from Dave

[VK3DXE]

My other concern with this would be where optimal performance is with these yagis, gain and pattern-wise, with or without the new DE Adam.

Have you had an opportunity to at least do a rudimentary polar plot?

[VK5PJ]

It's nice being able to "see" what's going on now.
This is a R/L sweep of the 23CM35, with the DE returned to the stock standard position.

Hi Adam, may I ask what the softare package is that you used to get the data from the analyser? I have a HP spec-an/tracking gen and would like to get a display on my pc (after I buy a GP-IB card)

Peter, vk5pj

[VK4GHZ]

indeed great news, but i must ask, what can you see as a difference between the 2 driven elements?

Dave, I cannot see much difference at all.
Have just taken these pictures.



Old on top of new

The old one is bent out of original shape with all the tweaking, but overall dimensions look the same.
I'm not game to open the access hatch, or risk taking off the adhesive heat shrink on the new one to investigate any further, but perhaps there was a problem with the RG316 coax inner that runs inside the hollow tube on one side?

My other concern with this would be where optimal performance is with these yagis, gain and pattern-wise, with or without the new DE Adam.
Have you had an opportunity to at least do a rudimentary polar plot?

Alan, I don't understand your concern.
The yagi now behaves as advertised, so I have no further reason to doubt it's claimed performance, and I haven't done any polar plots.

Hi Adam, may I ask what the softare package is that you used to get the data from the analyser?

Peter, I am using a WindFreak SynthNV.
Really cool!
Might do a video on it, as still pictures and words cannot explain how neat these devices are.

I have a HP spec-an/tracking gen and would like to get a display on my pc (after I buy a GP-IB card)

S T O P!!!
A Prologix USB interface is the modern way to go.
viewtopic.php?f=22&t=10164&p=20739&hili ... gix#p20738
If you eventually replace your PC, chances are there will be a new card slot format.
USB will be around for a long time to come, and the USB Prologix interface can be used with both the desktop machine, or the Notebook.

There are cheaper GPIB USB interfaces found on eBay, but beware!
Even KE5FX (make sure you check out the Toolkit link in the Prologix topic I pasted above) recommends the Prologix device.
I use the KE5FX "7470" package with my HP-8562A, and with 7470 running, it takes only one function key press to grab a spectrum analyzer screen shot.
Would recommend the Prologix USB adapter and KE5FX software for any GPIB instrument.

[VK4FLR]

Hi Adam - extremely interested in the WindFreak SynthNV you mentioned & its sweep capability - this might help solve our lack of access to test equipment up here in the bush especially with our 2.4ghz transverter construction project which you so generously helped us with, re the PLL programming corrections & general advice recently . .. would be interested in any video /comments on the Windfreak device re its accuracy & general usage ? might buy one based on your opinion ?? have been following this thread with a great deal of interest ! glad you sorted the problem out !

73's
frank VK4FLR

[ZL1RS]

Peter, I am using a WindFreak SynthNV.

Adam, I assume according to http://www.windfreaktech.com/docs/synthnv/wfapp1_1.pdf ?? As a matter of curiosity, what was the directional coupler you used?

I've been looking into "plotting" type antenna analysers and the WindFreak SynthNV + directional coupler is of interest to cover higher frequencies than the HF to 180/200/230 MHz offerings like the AIM4170C / SARK-110 / Rig Expert AA230.

Unless I missed something, the WindFreak doesn't go down to HF ... otherwise a big chunk of HF/VHF/UHF/SHF Amateur spectrum could be covered with that and 2 or 3 directional couplers!

73

[VK4GHZ]

This is a segment of a bigger video production... that never happened.

As a part of a recent club Tech Talk presentation, I decided to finish this bit as a self contained video.
Using a SynthNV to sweep an M2 23CM35.

[VK2KRR]

I'd probably try not to use a metal ladder as a stand. Do u think thats a bit close or would not affect the reading ?

PS- awesomely well put together video

[VK4GHZ]

I'd probably try not to use a metal ladder as a stand. Do u think thats a bit close or would not affect the reading ?

PS- awesomely well put together video

Hi Leigh
The yagi was over 2 wavelengths away from the metal ladder, so I don't believe the proximity to it had any negative effects.
In theory, firing up into the sky like this, if the reflector is doing it's job properly, it could have been closer to the ground.

[VK2KRR]

Point up is all good, I was just concerned with the ladder. Should be easy to do a comparison with something non conductive if u wanted to and see if there is any difference out of curiosity.
Can you save or get a screen capture of the initial graph ?

[VK4AQF]

My feeling is that their DE/D1 design is out somewhat. Match by altering the DE length or some method (depends on type here maybe harder to change) other is alter D1 spacing which has most effect usually.
Fingernails noted. Im also sure my finger is the perfect tuning toll for frequencies above 1000MHz!!