Prototype Cheap Yagi N Socket Bracket

Well, as mentioned in the previous post I forgot about todays lunchtime net – even after telling everyone it'd definitely be on. Again, I apologise for that. But here is the post detailing what I was doing…

Today I designed and fabricated a bracket to hold an N socket for connecting to my 70cm cheap yagi (see photos and video below). The idea being, that the main body of the bracket will be attached to the boom and flush up against the part of the driven element which the shield of the coax is connected too. Then, the center pin of the socket is mounted such that it lines up with the 'J section' of the driven element. From the center pin a piece of copper wire will be soldered and then will connect to the J section through a hole drilled in the element and then wrapped around it (and possibly also soldered for extra strength). Finally (or, probably first up) the bracket will simply be hot glued to the boom to minimise any additional metal.

Hopefully this all works out, but I have three concerns:
1. All the extra metal for the bracket – hope it doesn't disrupt things too much;
2. The quality of the connections – I don't have the equipment (nor skills – yet) to be able to solder to aluminium; and
3. The strength of the bracket with only hot glue – time will tell if I need to screw it to the boom for strength.

But, at least I finally have a design for the bracket, so from here I can do as many iterations as I'm willing to perfect it – first of which is for the planned 2 4el 2m beams for stacking. But here's to the prototype!!

(Oh, on a side note. I've also modified the reflector and DE length of the beam after modelling with 4nec2 so that the beam will be targeted at 439MHz instead – so that I can use it for FM as planned. The changes got the SWR down to about 1.2:1 for about 438 through to I think about 450 – and still with a gain of around 11dBi and a good F/B ratio. Once I've tested the SWR, I'll share the details and NEC model for any interested.)

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Oops!! I forgot it was Thursday today!

Sorry everyone, I forgot today was Thursday and thereby totally forgot about the lunchtime net. I'm truly in holiday mode and as a result was fabricating a socket bracket for my 70cm cheap yagi. I'll post up some pics and details later, but for now I just wanted to apologise about the net.

I promise it'll be on next week. I'm updating my calendar reminder now.

Sorry. :/

More on 435MHz WA5VJB – High SWR

As previously mentioned, after completing the basic build of an 8el version of the WA5VJB Cheap Yagi for 435MHz, I found the SWR to be so high as to be unsable (for that part of the band). I've now gone away and done an NEC2 model to see if the issue was the design or the build.
 
Well, all I can say (and I add the disclaimer here that at best I'm a beginner NEC modeller) that it appears to be an issue with the design. From what I can see from the model, this beam was doomed to fail from the start with an SWR approaching 3:1 at 435MHz.
 
Anyway, I've attached the model and a capture of the SWR graph for your perusal. Feel free to have a play, and if I've got it wrong let me know. But so far, the model confirms the physical implementation – which I'll now simply use for SSB at the bottom of the 70cm band, and as a practice platform for adding a socket.
 
I might now go away and do a model of the Cheap Yagi targetted at 432MHz…
 
Quick Note: I did find if I changed the length of the DE from 13.0" to 12.7" that I could get the SWR down around 1.6:1 at 435MHz and another dip at 441MHz with an SWR of around 1.4:1. More playing with the optimizer might yield even more improvements…. Ahhh, so it does… Changing the reflector from 13.4" to 13.06" resulted in an SWR around 1.36:1 from 435MHz to 441.3MHz where it drops to it's lowest of 1:31:1!! If I was to do this, then the beam would cover the FM portion of 70cm like I was after!! I wonder how feasible this is now that I've varnished it… (Oh, and it still has a reasonable pattern – albeit reduced F/B ratio – with a gain a bit over 11dBi.)
 

435mhz_8el_wa5vjb

Define HSWR on a FT-817ND

Well, in my previous posted I commented on the readings for the 435MHz WA5VJB I built up – which I've just put the last coat of varnish on. During this I mentioned my FT-817ND was reporting HSWR but I was not sure what ratio this translated to.

Well, after trying to tune up my 15m/40m dipole yesterday on 10m – and failing – I can now report what it is. Due to using a different VSWR meter for HF I was able to get a proper reading. It appears that HSWR on a FT-817ND translates to approximately 2.5:1.

So this means, that beam is no where near suitable for 435MHz!! So I really need to spend a bit more time here in front of this computer this holiday and build a model. Quick sticks! (But in the mean time, I think I've come up with a design for the socket mounting….)

Progress of Cheap 70cm Yagi

Well, my hopes for last week-end didn't quite work out, however today I did finally got back to building the cheap yagi for 70cm.

I attached the mounting bracket and then thought that before I put the varnish on I should put it up in the air and do some tests. Well, things weren't quite as hoped.

Basically, it looks as though the beam is tuning way down the bottom of the band – essentially just like the version for 432MHz. This is not too surprising, as the radiating element is identical to that for 432MHz, but still I was hoping the changes to the reflector and D1 (of 0.1") would result in the needed improvement in tuning. I'm thinking now I need to model it up and see what NEC can tell me.

But none the less I noted the basic SWR details. This time due to low power I was not able to use my SWR meter (couldn't get enough power through it to calibrate it) so I used the SWR meter on the FT-817 instead. It showed the following:

1:1 from 430MHZ – 433.295

Then it increased quickly with the FT-817 reporting HWSR at 435.895. Now I'm not sure what the FT-817 considers a High SWR, but I'm going to guess it's at least 2:1 – but the SWR meter on the FT-817 is only about about half – so maybe 1.5:1???

Anyway, that tells me it's definitely only useable at the bottom half of the 70cm band, and even at the designed frequency it's still rather high. Really, you'd only use this at 435MHz if you had no choice, and definitely not up at 438MHz like I was aiming for.

So, what could have caused this? Well, I did use an element thickness twice the designed diameter (as that was the smallest aluminium I could find); and as you go higher up the frequencies the tolerances are definitely reduced, so I guess that's it. But to be sure, I'd like to model this up as per the design, and then increase the thickness and see the result. Will keep you posted.

As for what I'll do with the beam… hmmm.. Guess I might as well just finish it anyway and accept it's for 70cm SSB – not 70cm FM as hoped. Plus I still need to figure out the mechanical mounting for the connections – as I'll then use that on the two 2m beams for phasing I have planned.

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Progress of Cheap 70cm Yagi

Well, my hopes for last week-end didn't quite work out, however today I did finally got back to building the cheap yagi for 70cm.

I attached the mounting bracket and then thought that before I put the varnish on I should put it up in the air and do some tests. Well, things weren't quite as hoped.

Basically, it looks as though the beam is tuning way down the bottom of the band – essentially just like the version for 432MHz. This is not too surprising, as the radiating element is identical to that for 432MHz, but still I was hoping the changes to the reflector and D1 (of 0.1") would result in the needed improvement in tuning. I'm thinking now I need to model it up and see what NEC can tell me.

But none the less I noted the basic SWR details. This time due to low power I was not able to use my SWR meter (couldn't get enough power through it to calibrate it) so I used the SWR meter on the FT-817 instead. It showed the following:

1:1 from 430MHZ – 433.295

Then it increased quickly with the FT-817 reporting HWSR at 435.895. Now I'm not sure what the FT-817 considers a High SWR, but I'm going to guess it's at least 2:1 – but the SWR meter on the FT-817 is only about about half – so maybe 1.5:1???

Anyway, that tells me it's definitely only useable at the bottom half of the 70cm band, and even at the designed frequency it's still rather high. Really, you'd only use this at 435MHz if you had no choice, and definitely not up at 438MHz like I was aiming for.

So, what could have caused this? Well, I did use an element thickness twice the designed diameter (as that was the smallest aluminium I could find); and as you go higher up the frequencies the tolerances are definitely reduced, so I guess that's it. But to be sure, I'd like to model this up as per the design, and then increase the thickness and see the result. Will keep you posted.

As for what I'll do with the beam… hmmm.. Guess I might as well just finish it anyway and accept it's for 70cm SSB – not 70cm FM as hoped. Plus I still need to figure out the mechanical mounting for the connections – as I'll then use that on the two 2m beams for phasing I have planned.

Cheap70cm_001_1Cheap70cm_002_1

Started 70cm Cheap Yagi

Well, while also studying for my upgrade and learning CW I've still got some beam builds planned. As such, Friday night I got started on the 70cm Cheap Yagi I want to build. I'm doing the 8el one targeted at 435MHz in the hope that'll give me a good SWR in the FM Simplex segments of 70cm (433.750MHz – 434.250MHz and 438.750MHz – 439.250MHz). This is because my Cushcraft 11el 70cm beam was purchased for 70cm SSB work and as such is centred way down the other end of the band and has no chance of a suitable SWR, but hopefully this will.

This will hopefully allow me to run some lunchtime 70cm nets and also have a play around with some longer distance 70cm FM. Should be interesting me thinks.

Anyway, today I finished cutting and bending all the elements, and attaching them to the boom. Hopefully tomorrow (Sunday) I can drill the holes for the mounting bracket and then start applying the varnish. After that I've got to figure out how I will attach the cable. I'm hoping to come up with some kind of mechanical mounting system (so a bracket/clamp) this time, as aluminium is too much hassle to solder to. I also want to figure it out here as I intend to do the same fo the two 2m ones I wish to build to stack.

Oh, and this time I made the holes nice and tight so no hot glue is required to hold them in place. However I am going to hot glue them once all the varnish is done – just for added strength.

Well, that's about it. More pics to follow, and hopefully I'll have it done in time for the holidays – although the socket mounting could trick me.

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