Odd signal results from Zinwell- AV-COM combination

[Anonymous_1]

The feedarms are not the same for a CM240 without sub reflector, the sub reflector is mostly used for uplinker.

The feedarms and LNB support are more longer without the subreflector option . I don't have it without subreflector, I made my onw LNB holder for Cband but not perfect.
For KU or KA band you can use the subreflector the SNR (C/N, etc) is the same with or without subreflector. (my experience)

PS: related thread: Dimensions for Channel Master 2.4m Feed Arms

 

[blademedia]

I can provide accurate measurement's from my 2.4 with standered arms nelson if required.

 

[nelson_b]

The feedarms are not the same for a CM240 without sub reflector, the sub reflector is mostly used for uplinker.

The feedarms and LNB support are more longer without the subreflector option . I don't have it without subreflector, I made my onw LNB holder for Cband but not perfect.
For KU or KA band you can use the subreflector the SNR (C/N, etc) is the same with or without subreflector. (my experience)

PS: related thread: Dimensions for Channel Master 2.4m Feed Arms

Thanks for the info ... and link to the related thread

 

[Anonymous_1]

I can provide accurate measurement's from my 2.4 with standered arms nelson if required.

Yes, please if possible.
Thanks in advance

 

[nelson_b]

I can provide accurate measurement's from my 2.4 with standered arms nelson if required.

Yes indeed that could be useful to me .... what type of K/u l.n.b holder arrangement do your standard arms have?....

 

[blademedia]

@Feedsat_DXer @nelson_b when I say standard there the same as this with standard holder.


If the above type measurements are useful let me know and I will go and measure them,

In the near future when I install this dish I will be doing away with them and doing a modification of my own.

 

[nelson_b]

@Feedsat_DXer @nelson_b when I say standard there the same as this with standard holder.
View attachment 108205

If the above type measurements are useful let me know and I will go and measure them,

In the near future when I install this dish I will be doing away with them and doing a modification of my own.

yes certainly the measurements could be useful to me ... do the arms on yours connect to the dish side and bottom like the 1.8 arms do .. see pics

 

[blademedia]

Hi nelson yes that how it connects same as the 1.8,

Ok the side arms are identical to your 1.8 apart from being 505mm longer


Things alter on the bottom arm it has a slight bend at the LNB end, the 1.8 is straight, I will get back to you on this with accurate measurement's and angles.

 

[nelson_b]

Hi nelson yes that how it connects same as the 1.8,

Ok the side arms are identical to your 1.8 apart from being 505mm longer
View attachment 108208

Things alter on the bottom arm it has a slight bend at the LNB end, the 1.8 is straight, I will get back to you on this with accurate measurement's and angles.

Great --- whenever its convenient for you .

I would like to make up some arms - and see if the k/u performance is any different using a regular offset setup - from using the sub reflector setup, which i must say is good, and will take some beating i think

I like the arrangement i have on the 1.8 it has proved itself well over the years, and would like to create similar on this 2.4 if possible.

 

[blademedia]

Hi nelson as mentioned the side arms are identical to the 1,8 but 505mm longer, total length is 1975mm to bend,


I'm trying to explain this the best I can ok here goes

Above is the dish end 80mm the center of bend


Above is LNB end 60mm to centre of bend

Above is centre between both bends the straight part/middle section 1380mm


Above is the overall length including bends,



Above is to show you what way the bends go red is the dish end, blue is the LNB end, I will get you the angles tomorrow, anything ive missed please let me know.

 

[nelson_b]

That,s great B.M. - thanks if i think of anything else - i will indeed ask
Again - whenever is convenient for the angles...... as you know things don,t move very fast here ..... i have quite a lot on this week

 

[blademedia]

Ill check tomorrow nelson, hopefully the angles are the same as the 1.2/1.8 then you only have to remove a arm and put the same angle on the new arm.

 

[RimaNTSS]

when i set up my l.n.b support i was working on the basis of the l.n.b probes being at the same spot as the central point of the sub reflector

This is not right..... On the Gregorian design the Focal point of the dish is co-located with one of the ficiies of the subreflector ant this is not central point of it.
Wherever you place LNB and then tune antenna to maximal possible signal then any movement of the LNB will cause worsening of the signal. But that does not mean that LNB is in the right spot! The best way how to check whether LNB is in right position is to tune antenna to the maximum signal and then check leaning of the "face" of the dish. It is well known that CM 2.4m has an offset angle 22.62*, so if you have tuned to the satellite with elevation 22.62* than the face of the dish should be dead-plumb, simple like that. IMHO, it does not matter what is the length of the feedarms (they can be quite different ).... more important is that LNB holder used is holding LNB in proper position and points LNB towards proper point on the surface of the dish.

 

[nelson_b]

This is not right..... On the Gregorian design the Focal point of the dish is co-located with one of the ficiies of the subreflector ant this is not central point of it.
Wherever you place LNB and then tune antenna to maximal possible signal then any movement of the LNB will cause worsening of the signal. But that does not mean that LNB is in the right spot! The best way how to check whether LNB is in right position is to tune antenna to the maximum signal and then check leaning of the "face" of the dish. It is well known that CM 2.4m has an offset angle 22.62*, so if you have tuned to the satellite with elevation 22.62* than the face of the dish should be dead-plumb, simple like that. IMHO, it does not matter what is the length of the feedarms (they can be quite different ).... more important is that LNB holder used is holding LNB in proper position and points LNB towards proper point on the surface of the dish.

Thanks for your input here - RimaNTSS

Setting the support so that the C band l.n.b.probes were at the central point of the subreflector was my starting point and i got a signal ... since then i,v made many slight changes in height and distance to optimize the signal .. so i doubt it is at that point now.
the good signal strength i,m getting from some transponders makes me think i,m quite close to optimum. with C band on this dish ...The AFN transponder at 1 west is giving me 9.5 db .. that,s 2.0 db more than i get on the 1.8 and around 1.0 db less than i used to get with the 3 metre Prodelin ... the closest sat to
elevation 22.62 at my location will be 26 east (23.1 elevation according to dishpointer) .. i will see if i can locate one of the data transponders there and measure the dish face for almost plumb ...
regards ....

 

[RimaNTSS]

the closest sat to
elevation 22.62 at my location will be 26 east (23.1 elevation according to dishpointer) .. i will see i can locate one of the data transponders there and measure the dish face for plumb ...

Satellite with elevation 22.62* was only an example. Any satellite can be used to do the offset-angle test. If you use 26*E for this test than maximum signal should be achieved when dish is leaning backwards 0.5*. But it is better to do this experiment on your true-south satellite.

 

[RimaNTSS]

Forgot to tell: When antenna is polar-mounted "Offset angle test" can be done only on true-south satellite. When antenna is on Az/El mount then test can be made on any satellite.

 

[Captain Jack]

Interesting test. Will give this a go on mine - probably miles out!

 

[nelson_b]

Struggling to find a straight piece of timber here in my stores to put against the dish face ... and its pouring with rain here right now ... reasonably confident that i,m not far out though, from the signal strength that i,m getting in general from 1 west --and 10 and 38 east ... its all good fun, much more interesting that going to work

 

[RimaNTSS]

In furniture shops they sell metal (aluminum) profiles, I think they are up to 3m long . They can be used as a tool for tuning of sat-antennas . In fact, some branded antennas (CM is one of them ) there are several places on the mount where is possible to attach inclinometer and find out the leaning angle of the dish "face" .

 

[nelson_b]

In furniture shops they sell metal (aluminum) profiles, I think they are up to 3m long View attachment 108226 View attachment 108227 . They can be used as a tool for tuning of sat-antennas View attachment 108228View attachment 108230 . In fact, some branded antennas (CM is one of them ) there are several places on the mount where is possible to attach inclinometer and find out the leaning angle of the dish "face" View attachment 108229 .

I found some aluminium U shaped channel in my shed that does the job nicely
Dishpointer gives 28.2 elevation for 0.8 west (my south sat) at my location .. so i can expect my dish to lean back 5.58 at best signal strength on AFN transponder ?...
here is my result ....

with a little over 0.3 out i,m pretty happy with this for C band