strange C2PLL operation...

[Cham]

Have been having trouble with some TPs, various satellites lately. Finally had the time to play around with the system, checking connections, switches, power supplies, etc. All seems good. Dish pole still vertical to less than 1/10 of a degree so that's good. Brought out the step ladder to check the LNBF, played around with skew, focal distance, angle to the dish, etc, no real improvement... if not made it worse. Just by chance I decided to turn the LNBF upside-down from where it was set and presto! Signals back where they should be. Really odd...

Nothing was found in the LNBF throat other than a bit of dust inside the cover which I cleaned off before moving the LNBF assembly. The heat sink now faces about 10 o'clock instead of 4 before.

Was using 4100 H on 97W to check, was having trouble with this TPp as well as one on 101W. They are both coming in fine now better than 13dB s/n (was 11-12 before).

Funny how things work sometimes...

 

[KE4EST]

I have done the same before. Just goes to show you the dish is not perfect. You are getting a better reflection from the other side.

 

[beavs2112]

Glad to hear you got it back up to snuff again
This is completely off topic but did you get that 3.0m Andrew dish? The reason I'm asking is I am picking up a used one next week

 

[Cham]

Yep. Just haven't had a chance to assemble it. Kind of looking for a polar mount I can use it on, but haven't come across anything heavy duty enough yet. Getting late in the season up here hoping I can at least get it up and running temporarily stationary before the winter hits. Would be nice to have two 10' dishes that track though.

 

[Titanium]

Look into the feedhorn throat and notice that the polarity probes enter the cavity from one side and extend approx 3/4 across the cavity.

Signals entering the feedhorn converge, cross and are reflected from the feedhorn wall and once again converge in phase at the probe. Ideally the probe will receive all reflected signal paths in phase, but this is near impossible due to mechanical accuracy of the reflector and feed. By rotating the feedhorn, the probe was simply placed in a position that collected more in-phase signals. You will likely find that if the system is tuned to another transponder, polarity or dish swing to a different satellite, the signal quality reading (BER - Bit Error Rate) might be better if the probe was in the original position.

Optimization is easier with a single polarity and fixed dish. Each mechanical parameter of the reflector and feed can be set to optimize for a specific transponder. This can attenuate adjacent satellite interference by reshaping the lobes, optimizing cross polarity separation, peaking for optimum efficiency and phasing of the target signal. Optimizing for a single transponder on a motorized dish will likely result in decreased performance on other transponders and satellites.

Optimizing a motorized system is about compromise...

 

[Cham]

Hi Brian,
Agreed, motorized systems are somewhat compromised. Tuning for one polarity and transponder frequency will affect others. So far though I have not seen any problematic signal drops, and many are higher than before, so as KE4EST suggests the dish might be just a bit warped causing a better focus from one side or another, this is an old fiberglass dish and passes the string test, but may have some surface abnormalities from being in use for 20+ years in the elements.
If it was worse I would consider switching out the fiberglass dish with the solid aluminum Andrews dish I have not set up yet, but this minor tinkering seems to have the original 10-footer working well once again.

Think I have mentioned before regarding setting focal depth, polarity, and scaler position. This can be an extremely delicate operation when trying to maximize several TPs over the whole C-band spectrum; lots of measuring and re-adjusting and re-measuring to optimize the weakest signals without over-compromising stronger ones. It takes time and patience to get it all working...sometimes at least. It's good time spent though, the results are quite rewarding!

I may have mis-labeled this thread... suggesting a "problem" with the C2PLL LNBF, where the issue was really with the whole setup as a receiving antenna system, and how the parts work together as a unit. I certainly don't mean to pick on the LNBF. I actually think it works better than the Chaparral feedhorn/LNB corotor I was using previously... that is; more consistent signals over the band than I could achieve with the corotor. Expensive PLL LNBs might have worked too, but this is so much simpler and cheaper!

 

[Titanium]

I didn't take it wrong. No worries!

Understood what you found and why your solution improved the reception. Thought that I would turn your finding into a learning moment for others.

 

[wvman]

Have been having trouble with some TPs, various satellites lately. Finally had the time to play around with the system, checking connections, switches, power supplies, etc. All seems good. Dish pole still vertical to less than 1/10 of a degree so that's good. Brought out the step ladder to check the LNBF, played around with skew, focal distance, angle to the dish, etc, no real improvement... if not made it worse. Just by chance I decided to turn the LNBF upside-down from where it was set and presto! Signals back where they should be. Really odd...

Nothing was found in the LNBF throat other than a bit of dust inside the cover which I cleaned off before moving the LNBF assembly. The heat sink now faces about 10 o'clock instead of 4 before.

Was using 4100 H on 97W to check, was having trouble with this TPp as well as one on 101W. They are both coming in fine now better than 13dB s/n (was 11-12 before).

Funny how things work sometimes...

I've noticed that a 71/2 foot dish is marginal on SES1. For MeTV HD, I have never got a signal level above 50/49, which stays locked with no breakup unless there's thick cloud cover or hard rain. I've rolled one of my 10 footers to SES1 and had similar signal levels. Using the same 71/2 foot Unimesh dish, I can park it on Galaxy 19 and have a 90/85 signal level on all the channels. I have channels on Galaxy 16 that really shouldn't be locking with a signal level of 55/45.

THIS, COZI and a couple other channels are as low as 50/45 and they stay locked even in bad weather. All the other channels on SES1 and Galaxy 16 are in the 85/75 range, and some of them are the same polarity as the weaker channels. I've even seen channels like H&I be at a 55/50 level for several hours, and go to 85/75 later in the day. All the other channels in the MUX are much higher.

Even the other H&I feed is much higher than the other one. I believe a lot of it has to do with power levels at the provider, and the age of the satellite and atmospheric conditions. I've seem some weird things happen, especially with the equinox changing. I've even seen channels with a 90/85 signal level break up for no apparent reason. With levels like that, you'd think there would be no break up, but it happens.

I'm about to embark on a new adventure. Just ordered a Linkbox 9000i. We'll see how that goes.

 

[Cham]

Can't rule out terrestrial interference being an issue too. I just found out a tower was installed a few months ago due south of me maybe 3 miles away and they are using wimax to distribute broadband to their customers. Talking to a buddy today at one of the government departments that organizes RF spectrum and they have had complaints from one of the other local service providers, as well as from the municipal airport nearby. Looks like the tower is almost in line with the runway??? Unreal!!
Might have to rent out my cutting torch...