Low threshold receivers

[Keith Brannen]

Interesting discussion, especially about the differences in where a receiver will lock on and display a weak signal. Makes me very glad I bought a Pansat 3500SD to begin with. When I think of all the times I pointed dishes and hand-held LNBs (and even hand-held 60e dishes!) searching for a glimmer of a signal, I would hate to think of how I would have missed that first indication of being in the right area if I had been using a different receiver that wouldn't display anything until it got a lot stronger signal.

Perhaps that is why some people have more trouble aiming their first dish than others, they may pass right by it because of their receiver's threshold.

Linuxman, what size dish are you using that you get 45% on the National Labs test card? I get the same signal quality on my 80cm (and my LNB is 6 degrees off-centre, and it is 9 degrees away from the top of my arc).

 

[linuxman]

Linuxman, what size dish are you using that you get 45% on the National Labs test card? I get the same signal quality on my 80cm (and my LNB is 6 degrees off-centre, and it is 9 degrees away from the top of my arc).

It's only 10 foot but it is on a polar mount for moving across the arc.

The explanation for that is, the bigger the dish, the more accurately it has to be pointed and adjusted especially if you want to get the best signal across the arc.

 

[Keith Brannen]

It's only 10 foot but it is on a polar mount for moving across the arc.

LOL! "only" 10 foot!

The explanation for that is, the bigger the dish, the more accurately it has to be pointed and adjusted especially if you want to get the best signal across the arc.

I understand now (especially how the accuracy would have to be much more precise than for a smaller dish), and was wondering if it was a stationary dish, or one that travelled the arc.

 

[turbosat]

Linuxman says The explanation for that is, the bigger the dish, the more accurately it has to be pointed and adjusted especially if you want to get the best signal across the arc.>quote
I would also say, the taller your trees and bushes are, the sharper your chainsaw's chain must be kept!

For what its worth, on my primestar 1m, on a polar mount/linear actuator I get Nat'l Labs 12060 at 74/74, on my VS Ultra, most channels on that bird come in, as McCloud used to say, like a high wind. For curiosity I looked at White springs, same dish/receiver, getting 65/63 but signal could be better-my polar mount needs a tiny amount of tweaking east/west,just been afraid to go mess with it since it's so easy to go too far.
I have my first dvb which is a Coship 3188C, primitive receiver, but I think it has better threshold than this ultra, or my Traxis 3500. Scans in everything, but is slow as molasses. Only use it for dish tweaking now, when I need to.

 

[linuxman]

I understand now (especially how the accuracy would have to be much more precise than for a smaller dish), and was wondering if it was a stationary dish, or one that travelled the arc.

To illustrate the difference in dishes sizes surface accuracy etc, on the Birdview, that same frequency is at 75% SQ on the Pansat and it is only an 8 footer. That's after it was adjusted to get best signal across the arc. Before the adjustment it was at 95% SQ.

On the Unimesh prior to adjustment it was at 65% on the Pansat.

Perhaps that is why some people have more trouble aiming their first dish than others, they may pass right by it because of their receiver's threshold.

I would have to agree 100%.

 

[linuxman]

So I still haven't gotten but a couple of answers to my original question.

What are some other brands, makes, models of FTA receivers that we don't hear about much, that have blind scan, handle motors well, handle multiple diseqc/22k switches well, have ac3 passthru, you get my drift?

Plus have a low threshold for receiving low signals?

Much thanks to the couple of responses I did get.

 

[Mr Tony]

I know on my various receivers the meter and threshold is different

Pansat 1500 goes from 10-99 with threshold around 25-30
Coolsat 5000 is from 63-85 with threshold at 65...but the meter sucks. Pansat can be at 45 or 60 and Coolsat shows 69.
Fortec Ultra is 10-99 with threshold of 40
Visionsat is 15-99 with threshold between 35-40
My old Pansat 2100 goes from 60-99 and sadly the meter sucks. If I have a 45 or a 75 on the 1500 the 2100 shows around 90.

But it also depends on the channel, symbol rate and FEC. I can get the Equity stuff on G10 KU at 25 and be stable (FEC 3/4) but the G3 stuff my 6 footer can lock it at 60 and it isnt stable due to the 7/8 FEC.

The test stuff on G11 seems low. my TS is 93 and those on G11 I get at 70 on the Pansat and 72 on the Coolsat

 

[hyper]

Hi:

The best comparison between receivers that indicates ability to pull low level signals from the sky is the tuner/receiver sensitivity, often expressed in dB. The lower down this rating, the greater is the detection capability for that receiver. The term "low threshold receiver often refers to any receiver below 7dB sensitivity (commonly). There are other measures for sensitivity, too.

Due to all manufacturers software differences (as there are no standards for displaying quality of signal via bar graph or percentiles), the SQ measure/display is fairly relative and hence inaccurrate for comparing true performance (i.e., is not absolute between different makes) so one brand's 20% SQ is potentially another brands 45% SQ, for example.

And, to be sure, most any sat's footprint varies by multiple dB across the entire boresight/main footprint terrain, as well as relative to the local noise level from other MW traffic that is terrestrial in nature. The footprints from Lyngsat do not consider any such local noise or interference but publish the theoretical values from the sat makers, mostly. And, let's not forget that atmospheric moisture drop for any Ku band signal - its a real killer (attenuator), yet has much less C band impact.

hyper

 

[linuxman]

Thanks Iceberg and Hyper,

I appreciate the answers, and explanations.

I took a few minutes to run up to the roof while my son watched the meter on the Traxis on G11 with the above freq and managed to run it up to a little over 60% SQ. I came down and checked the ends and there was no change on White Springs or AMC6 in SQ, so I must not have given the last elevation adjustment the other day when I hit the magic spot.

I was so happy to finally get it tuned in, I forgot.

So now I shouldn't have any loss of picture on the test cards under normal operating environments.

Fred

 

[kymics]

Hyper,
Welcome to SatelliteGuys! That was quite the answer for coming out of nowhere. So I'm curious, what's your background in sat?

 

[ghermai]

I agree with Anole. The issue is receiver sensitivity , which meanse that the smallest signal a receiver can detect befor it hit the noise floor.

This test can be done easily by inputing a variable Attenuator (75 Ohm) between LNB and Receiver input. Adjust it the attenuator till you loose the Picture and write the Signal Quality number for both receivers. Remember the Signal Quality number is not the same for each receiver. This will give you a good apple to apple comparison.

Good Luck
Ghermai

 

[linuxman]

This test can be done easily by inputing a variable Attenuator (75 Ohm) between LNB and Receiver input. Adjust it the attenuator till you loose the Picture and write the Signal Quality number for both receivers. Remember the Signal Quality number is not the same for each receiver. This will give you a good apple to apple comparison.

That would be great is I know what an Attenuator was, and then where to get one.

Sorry, I am not an electronics genius.

 

[wshillington]

Hi:

I used to have a Fortec Ultra. It seemed to work well. It would blindscan and seemed to pick up all the stations. Anything with a signal level of 30 or above would be picked up okay. My friend has a Coolsat 6000. He seemed to pick up most of the stations I could. He needed a signal level of 70 but it seemed that any station I was getting at a level of 30............. he was getting at a level of 70............. I expect the two receivers were getting the same level but showing it differently. I replaced the Fortec with a Viewsat Ultra and I really like this receiver. It also has a fairly decent blind scan. This receiver will pick up stations with a level of 25................ but again I think it just reads the level differently then the Fortec and the Coolsat................. it picks up the same stations.

cheers
Bryce

 

[qwert1515]

I agree with Anole. The issue is receiver sensitivity , which meanse that the smallest signal a receiver can detect befor it hit the noise floor.

This test can be done easily by inputing a variable Attenuator (75 Ohm) between LNB and Receiver input. Adjust it the attenuator till you loose the Picture and write the Signal Quality number for both receivers. Remember the Signal Quality number is not the same for each receiver. This will give you a good apple to apple comparison.

Good Luck
Ghermai

I don't think the best way for a comparison is with an attenuator (a device like a big resistor), the receiver powers the LNB, if you place an attenuator between the receiver and the LNB you will reduce the current and voltage going to the LNB.

Also the attenuator might change the impedance of the system (receiver to lnb) which could give different results on different receivers, depending on their sensitivity over the L-Band spectrum.

I am sure Anole will share his thoughts soon

 

[Anole]

you know me too well...

I don't think the attenuator idea is a generally attractive one for most people.
And I discussed other options, above.
However, here is something -close- to the sort of attenuator I was talking about (warning: PDF file).
They do come in 75 ohm versions, so that's a moot point.
The power to the LNB is a problem and would need to be routed around the attenuator in the usual way.

The idea with an attenuator, would be to put it in line between the receiver and LNB...
... set it for no attenuation...
. . . then slowly lower the signal (increase the attenuation) 'till you got a pixilated picture.
Then, note the Q-rating on the receiver at this point as a reference.
You might also note how much attenuation (how many db) you had to apply before screwing up your signal.

And I do think that "pixelated picture" should probably be the criterion, but that's up for argument.

When comparing two receivers, you'd have to do them within minutes of each other.
Or do 1, 2, 1, 2, and see if the numbers match.
Better yet, you should do them in parallel (at the same time).

What you would get, is how many db down from the nominal signal, each could hold a clean picture.
One would obviously be the winner.
Just being able to say brand X held 6 db longer than brand Y, might be a revelation!
Of course, that would only be taken as truth, once several other members confirmed.
You could also report to the group, what point on the receiver's Q-scale it lost the picture to breakup.
Hopefully, the latter would be useful to other members with that receiver.

But in summation, the problem with DC at the attenuator, getting a decent attenuator, using it within its rated frequency, cost, et al, just make it a harsh choice for most members, here.
So, we should probably find a more simple method.

(didn't help, did it? )

 

[linuxman]

I did google for attenuators, and found out what they were, but Anole is right when he says the cost might be prohibitive for someone not already in that line of business. The one I looked at had a knob that you turned and it was $170.00.

That would be out of my budget, but if someone here already had the equipment and wanted to do the experiment, I think we would all benefit from the results.