Need a second opinion.

**Optima Collins** · 21-11-11, 06:31 PM

Guys, I'm working on a solid 180cm ground mount and I'm only getting 2 transponders on IS8 at about 55-60%. The setup isn't ideal, as I will explain below, but I'm missing something so I'd like to get some feedback from you lot. You know, like minds thinking as one ....

Anyway, the transponders I have are 4020H and 3740H and coming well and clear. No other transponders are visible and I can't get a lock on the satellite. There are no obstructions and both the elevation and azimuth are fine, i.e. my satfinder peaks at the current position. The issue is that the dish was a throw-away and I had to beat 2 of the petals back into shape with a rubber mallet and a wooden parabolic guide I made for this purpose. I think I did a reasonable job. Also, the LNB is old and has seen better days.

So, my question. C-Band interference aside and allowing for the fact that the dish may not be perfectly parabolic along all sides, what other factors might be affect the missing transponders. From experience using similar junk, I should be getting more TP's, but this isn't happening.

Any help appreciated!

Cheers
OC

**weirdo** · 21-11-11, 07:38 PM

Not knowing your location I'd say 1.8 meter is on the small side especially if it has been panel beaten.

**beer4life** · 21-11-11, 08:07 PM

Originally Posted by Optima Collins

Guys, I'm working on a solid 180cm ground mount and I'm only getting 2 transponders on IS8 at about 55-60%. The setup isn't ideal, as I will explain below, but I'm missing something so I'd like to get some feedback from you lot. You know, like minds thinking as one ....

Anyway, the transponders I have are 4020H and 3740H and coming well and clear. No other transponders are visible and I can't get a lock on the satellite. There are no obstructions and both the elevation and azimuth are fine, i.e. my satfinder peaks at the current position. The issue is that the dish was a throw-away and I had to beat 2 of the petals back into shape with a rubber mallet and a wooden parabolic guide I made for this purpose. I think I did a reasonable job. Also, the LNB is old and has seen better days.

So, my C-Band interference aside and allowing for the fact that the dish may not be perfectly parabolic along all sides, what other factors might be affect the missing transponders. From experience using similar junk, I should be getting more TP's, but this isn't happening.

Any help appreciated!

Cheers
OC

G'Day Cobber,
Yes, you're right, there is something awry. There are 30 odd TPs on the Pacific Beam. They should scan in even if encrypted.
Possible causes.
Focal distance of LNB.
The radius of the dish curvature should be twice the focal length.
To add to that, the focal point is further back than the face of the LNB.
First of all, I would be checking or replacing the LNB.
I'll give it some more thought once you answer.
Kindest Regards, " The Druid ":.

**Snookums** · 21-11-11, 08:19 PM

you didnt get the dish from JD did you??

**mtv** · 21-11-11, 08:35 PM

If the dish is OK and the focal distance is set correctly, then I would suspect the 'old' LNB.

How's the cabling and in particular, the connectors?.. check for any signs of moisture ingress/corrosion.

**Optima Collins** · 21-11-11, 10:17 PM

Originally Posted by weirdo

Not knowing your location I'd say 1.8 meter is on the small side especially if it has been panel beaten.

I'm in Western Sydney and yes, a 1.8m dish may not be ideal, but I have already installed 2 of these at a nearby location, one on AS5 and another on IS8 and the signals are reasonably good. I pointed this one to IS8 instead of IS5 for MTV, in addition to the BBC and Australia Network.

OC

**Optima Collins** · 21-11-11, 10:19 PM

Originally Posted by Snookums

you didnt get the dish from JD did you??

Found it in a demolition site... a bit too late!

Originally Posted by Beer

... Focal distance of LNB...

Now, there's something to that Beer. I have a feeling you may be right. When I found the dish one of the petals was bent under one of the lnb supports. Whilst the lnb seems to be at the focus, it may be slightly out of alignment. Two things: (1) apart from a laser pointer, what would be the easiest way of checking that the reflections are actually hitting the lnb and (2) would a scalar ring improve matters, do you think?

Originally Posted by MTV

If the dish is OK and the focal distance is set correctly, then I would suspect the 'old' LNB.

How's the cabling and in particular, the connectors?.. check for any signs of moisture ingress/corrosion.

The cabling and connectors are new, I replaced those. I haven't replaced the lnb because the screws have rusted tight and I can't remove them without drilling. And, that begs the question, does lnb electronics lose selective frequencies with age?

OC

**beer4life** · 22-11-11, 11:10 AM

Originally Posted by Optima Collins

Now, there's something to that Beer. I have a feeling you may be right. When I found the dish one of the petals was bent under one of the lnb supports. Whilst the lnb seems to be at the focus, it may be slightly out of alignment. Two things: (1) apart from a laser pointer, what would be the easiest way of checking that the reflections are actually hitting the lnb and (2) would a scalar ring improve matters, do you think?

The cabling and connectors are new, I replaced those. I haven't replaced the lnb because the screws have rusted tight and I can't remove them without drilling. And, that begs the question, does lnb electronics lose selective frequencies with age?
OC

This should give you a good idea, without getting too involved.

Determining the focal length of a parabolic dish (axi-symmetric, circular)

Focal length = f
Depth = c
Diameter = D
f = ( D * D ) / ( 16 * c )
Measure the depth using a tight fishing line across the dish and a rule to measure depth c.

The radius of the curvature of the dish is 2f.

Kindest Regards, " The Druid ".

**Guiseppe** · 22-11-11, 11:22 AM

Originally Posted by beer4life

.. The radius of the curvature of the dish is 2f.

[/B][/SIZE]Kindest Regards, " The Druid ".
[/COLOR]

Umm. I thought dishes were parabolic.

**mtv** · 22-11-11, 02:00 PM

Originally Posted by Optima Collins

...... does lnb electronics lose selective frequencies with age?

OC

Have you checked inside the LNB/feedhorn for any ants/spiders/wasps/other crawlies, webs, corrosion, dirt/dust, moss growth etc?

Apart from the physical possibilities above, components do deteriorate with age and yes, it's not uncommon for some frequencies to be affected and some not/less affected.

**Optima Collins** · 22-11-11, 05:15 PM

Originally Posted by mtv

Have you checked inside the LNB/feedhorn for any ants/spiders/wasps/other crawlies, webs, corrosion, dirt/dust, moss growth etc?

Apart from the physical possibilities above, components do deteriorate with age and yes, it's not uncommon for some frequencies to be affected and some not/less affected.

MTV, other parameters aside, I think age may be an issue. The lnb is clean, I checked its insides. I may actually drill the screws off and replace it if I don't get a clean signal on the other TP's. At the moment I can hear my kids dancing to MTV China despite the rain and cloud cover, so that TP is coming through strong enough.

Originally Posted by Beer4Life

This should give you a good idea, without getting too involved.

Determining the focal length of a parabolic dish (axi-symmetric, circular)

Focal length = f
Depth = c
Diameter = D
f = ( D * D ) / ( 16 * c )
Measure the depth using a tight fishing line across the dish and a rule to measure depth c.

Actually, Beer, you gave me a very good idea. If I extend a piece of string or line from the dish vertex to the edges of the lnb aperture the distance should be the same on opposite sides. If it isn't then the lnb is not centred on the focal point, i.e. the signals are not entering the LNB horn at 90 degrees causing the loss of those TP signals that get reflected away. Averaging the measurements along the lnb circumference should equal the length of the hypotenuse (h) of a hypothetical right angled triangle from the apex to the lnb face with f-delta(f) (delta f being the distance from the lnb face to the true focus) as the adjacent side. Now, if I move the lnb so that all points along its circumference measure h to the vertex, then it should be aligned properly.

Cheers
OC

**carjackma** · 22-11-11, 05:28 PM

Originally Posted by beer4life

This should give you a good idea, without getting too involved.

Determining the focal length of a parabolic dish (axi-symmetric, circular)

Focal length = f
Depth = c
Diameter = D
f = ( D * D ) / ( 16 * c )
Measure the depth using a tight fishing line across the dish and a rule to measure depth c.

The radius of the curvature of the dish is 2f.

Kindest Regards, " The Druid ".

is there a similar formula for offset dishes as I was given a ex tab 2.4 offset dish without the feed legs??

**gordon_s1942** · 22-11-11, 05:29 PM

Although its only a 180cm, I have a Fibre glass Proline Off set dish gathering dust in my yard that I wouldnt mind seeing going to a 'Good Home'.
No mount or LNB supports unfortunately but I bodged up a mount and arms and had it working on C1 etc.
I have the manual for it safely hidden away somewhere and it has all the details for the mount, focal point etc.
I am only a couple of Sunday Driving hours west of Sydney so if its of use as I said I would like to see it go to a 'Good Home'.

**Optima Collins** · 24-11-11, 01:10 AM

Originally Posted by gordon_s1942

Although its only a 180cm, I have a Fibre glass Proline Off set dish gathering dust in my yard that I wouldnt mind seeing going to a 'Good Home'.
No mount or LNB supports unfortunately but I bodged up a mount and arms and had it working on C1 etc.
I have the manual for it safely hidden away somewhere and it has all the details for the mount, focal point etc.
I am only a couple of Sunday Driving hours west of Sydney so if its of use as I said I would like to see it go to a 'Good Home'.

That's very generous of you Gordon and I'd be very tempted, but I can't justify driving 4 hours for another dish, but I'm sure someone on this forum would like to have it ... if they haven't already sent you a PM.

Cheers
OC

**beer4life** · 24-11-11, 11:00 AM

Originally Posted by carjackma

is there a similar formula for offset dishes as I was given a ex tab 2.4 offset dish without the feed legs??

G'Day Cobber.
A little more complex I'm afraid.

You'll find the HDL_ANT program and description here:-

Kindest Regards, " The Druid ".

**porkchops** · 30-11-11, 01:03 PM

Optima Collins, Did you grab a new C-band LNB for this dish? As interested in the details if you have - due to having an ex-commercial solid dish sitting in my back-yard well overdue for my attention.

Would be interested to know what others have used for C-band, more specifically as to what and where to source an appropriate LNB from!

**Optima Collins** · 30-11-11, 04:32 PM

Originally Posted by porkchops

Optima Collins, Did you grab a new C-band LNB for this dish? As interested in the details if you have - due to having an ex-commercial solid dish sitting in my back-yard well overdue for my attention.

Would be interested to know what others have used for C-band, more specifically as to what and where to source an appropriate LNB from!

Hi there porkchops. No, I haven't attended to this dish yet. The rain in my area hasn't really stopped long enough for me to get around to it. What I can do is check my other C-band LNBs and get back to you. I can't remember off hand what they all are. I know one is a BAS and not a very expensive one at that with a noise rating of 17K, which is perhaps on the poor side, but it hasn't missed a beat on AS5 (solid 180cm dish), so I'm not complaining.

Likewise, the old LNB spoken of above on the beaten up dish is still working fine on ESPN (audio only since I have no subscription) and MTV China. If I can get BBC, Australian Network and MTV, I may just leave it as it is.

I normally shop at BASSAT on the Great Western HWY in Mays Hill (Western Sydney), because they're close by and reasonable (...if you're reading this guys, and I'm sure you are, I want a cut ...) or on eBay. The former have a good selection of gear and C band filters, should you need them.

Cheers
OC