Changed to Invacom LNBF, Q dropped

[JohninSD]

I wanted to get ION and NASA from 119W so changed my LNBF from a WSI DMX521 to an Invacom QPH031. It worked nicely but the Q on all the linear channels dropped by about half or a little less. The picture and sound look fine but I haven't watched very much since making this change so I don't know if I've lost anything in terms of viewability or not. What I'm wondering is whether it would be worthwhile to change the Diseqc switch from the DMS International DS-7241 to a Spaun SUR 211-WSG or to another higher quality Diseqc switch. Just on first look it seems it would help as the DMS switch lists a 3 db insertion loss and the Spaun claims less than 1 db. Anyone made this kind of change? What about using an in-line amp after the switch?

thanks,
John

 

[Lak7]

It's possible that the weight of the QPH has pulled your dish outta whack.

 

[guapoharry]

I had the same problem. The dish was working with a dual LNBF. Then, I installed a QPH-031. Signal quality went down a lot.

Try this:

While looking at the SQ, lift up a little on the LNBF body. When I did this, the SQ went up a lot.

To remedy this, I cut a wood block to wedge in between the LNBF body and the LNBF holder. The idea is here to counteract the effect of LNBF weight and torque on the plastic holder.

YMMV..

 

[Mr Tony]

It's possible that the weight of the QPH has pulled your dish outta whack.

yep. Thats why I dont use one. With my true south being 38 degrees it was very low and the QPH weighed down the dish arm resulting in poorer signal

 

[zamar23]

quapoharry

I'm surprised you needed to do it. Your dish has struts, and the setup looks so rigid including the LNBF holder.

 

[AcWxRadar]

I wanted to get ION and NASA from 119W so changed my LNBF from a WSI DMX521 to an Invacom QPH031. It worked nicely but the Q on all the linear channels dropped by about half or a little less. The picture and sound look fine but I haven't watched very much since making this change so I don't know if I've lost anything in terms of viewability or not. What I'm wondering is whether it would be worthwhile to change the Diseqc switch from the DMS International DS-7241 to a Spaun SUR 211-WSG or to another higher quality Diseqc switch. Just on first look it seems it would help as the DMS switch lists a 3 db insertion loss and the Spaun claims less than 1 db. Anyone made this kind of change? What about using an in-line amp after the switch?

thanks,
John

It's possible that the weight of the QPH has pulled your dish outta whack.

JohninSD,

It is correct that the Invacom QPH-031 is a very weighty LNBF (about 1.25 lbs to 1.5 lbs) and will pull your LNBF arm down lower from the "spot-on" alignment.

The best way to remedy this is to add "side-struts" to help support your LNBF arm. This way you can place any weight on the end of the arm and it should not move. This is a good thing to do regardless of what LNBF you put out there as it also keeps even the lighter LNBFs from bobbing in the wind.

With a dish antenna that is made with heavier gage metal, this should normally not be that noticeable, but it always helps regardless.

The best thing to do is remove the LNBF from the end of the arm, then measure and cut/fold two 3/8" aluminum tubes and attach them between the outer perimeter of your dish to the end of the LNBF support arm.

You want the arm to rest in a natural position as it was designed. Hopefully the arm was set spot-on from the factory and hasn't been bent out of shape in any way. When you attach these struts, that will beef up the entire assembly, but you may need to tweak the dish elevation angle to get it back to perfection if the support arm angle has been slightly angled. It does not take much to screw the focal point up.

With the addition of these support arms, you can put anything out on the end of the LNBF support arm, stopping short of doing chin-ups on it, and it will remain aligned.

Beyond that, there should be no degradation in your quality when upgrading to an Invacom QPH-031 LNBF. It should actually improve your signal in most cases. Sometimes the improvement is barely noticeable, but it should never be a reduction. The Invacom LNBFs are quality components and you should be able to trust them very explicitly.

Of course, there is always a chance that any LNBF could be different or weaker and even possibly defective, but with the Invacoms, I doubt that very much. I have used so many that I would personally vouch for them as being near to perfection in operation and consistency.

I think that all dish antennas should have these side struts to aid in supporting the LNBF arm. I won't buy an antenna that doesn't have them now... Now that I have seen how important it is.

RADAR

 

[phlatwound]

Here's a couple of pics of struts I added to a .9m Fortec. I made them out of elements from a scrapped OTA antenna, very light and strong.

 

[JohninSD]

Thanks for the suggestions -

I'm going to try the wooden block first - my dish is a WSI 9036 that has the struts as standard but the plastic LNBF mount could be bending a bit under the weight of the Invacom. I adjusted the dish tilt upward a bit and it brought in the 125W channels much better but then I lost the 101W satellite and those further East. I'll try the wedge and redo the alignment from scratch and see if that does it.

 

[starman345]

I can't endorse getting a Spaun to replace your DMS switch. I have lots of switches here, most of them cheapos, right now I'm using an old RocketTech 4x1 with my Prof 7301 card because the Spaun switches erratically with the card....and its the only one of the three or four I've tried that acts that way. It might be getting tired, its about 8 years old now.. anyway after trying many switches I am convinced more expensive is not necessarily better.

 

[Jim S.]

Beyond that, there should be no degradation in your quality when upgrading to an Invacom QPH-031 LNBF. It should actually improve your signal in most cases. Sometimes the improvement is barely noticeable, but it should never be a reduction. The Invacom LNBFs are quality components and you should be able to trust them very explicitly.

I haven't used a QPH-031, but I've used a DMX-521 which he says he upgraded from. The DMX-521 is listed with a slightly lower noise figure and a much higher gain than the QPH-031. (Although I've heard that advertised gain numbers are never to be relied upon.)

 

[AcWxRadar]

I haven't used a QPH-031, but I've used a DMX-521 which he says he upgraded from. The DMX-521 is listed with a slightly lower noise figure and a much higher gain than the QPH-031. (Although I've heard that advertised gain numbers are never to be relied upon.)

I haven't tested every LNB available, but I do use the Invacom QPH-031 exclusively now. It has become my standard.

When you apply any LNBF of this quality range (noise figure and gain) I gaurantee that you won't see a noticeable change in your signal quality. Definitiely you wouldn't see the degradation that JohninSD is showing here. For him, there must be another factor which is causing this. A one percent change or less (positive or negative) I would find acceptable and believable, but anything more than 2% change indicates that there is something else beyond the LNBF itself that is at fault.

Through my own personal experience, I find that almost all LNBFs operate the same. They either function nearly identically or they don't work at all (totally dead out of the box). I have not found any LNBF that works only half measure, yet.

JohninSD's situation seems to reflect some other problem or error and not the fault of the LNBF. I am not a gambling person, but I would place money on this one. There is something else wrong.

RADAR

 

[SATisfied]

yep. Thats why I dont use one. With my true south being 38 degrees it was very low and the QPH weighed down the dish arm resulting in poorer signal

Not to go off topic, but I thought you lived in Minnesota. How is your true south 38°? Wouldn't that put you over the Atlantic somewhere?

 

[Mr Tony]

sorry. I meant true south elevation

my true south sat is 93W

 

[JohninSD]

Readjusted dish, Q back up

I went through the dish adjustment again yesterday - Q went back up for the 125W channels - also getting ION nicely.

One problem turned out to be the latitude adjustment on the DG380 - there are scales on both sides of the mount and they don't read the same - so I split the difference and that seems to work OK. The scales aren't all that precise anyway.

That's all I plan to do for a while -

 

[turbosat]

john in SD, I think I had the same experience with that latitude scale on the DG380. If I remember it correctly, I was adjusting by the scale on the left side of the motor (looking from behind the motor) and it never quite matched up with what it was supposed to be. I just watched the tv at the dish, and quite tweaking when it was tracking properly, but that scale didn't read what it was supposed to. A few days later, I happened to look on the scale on the other side of the bracket, and it was dead on the exact latitude number!!