OTHER Invacom SNH-031 Universal LNB Off Frequency

[cyberham]

Yesterday I installed an Invacom SNH-031 universal LNB. I obtained this basically for free from a fellow leaving the hobby. This was a Cadillac of LNBs when it was used by some 20 years ago.

It is heavy! This makes you wonder how it differs in construction from a typical LNB. Probably some metal inside. It works beautifully except its local oscillator must be off frequency. It consistently scans transponders in at precisely 11 MHz high in frequency. Even with this characteristic, I decided to leave it installed to try it for awhile. I had to erase all scanned transponders on all satellites and rescan since 11 MHz is enough that they can't be locked without doing this.

Without any kind of frequency counter, could I open up the LNB while it is installed and perhaps tune the LO while monitoring a known satellite transponder on my receiver to correct this?

 

[primestar31]

Yesterday I installed an Invacom SNH-031 universal LNB. I obtained this basically for free from a fellow leaving the hobby. This was a Cadillac of LNBs when it was used by some 20 years ago.

It is heavy! This makes you wonder how it differs in construction from a typical LNB. Probably some metal inside. It works beautifully except its local oscillator must be off frequency. It consistently scans transponders in at precisely 11 MHz high in frequency. Even with this characteristic, I decided to leave it installed to try it for awhile. I had to erase all scanned transponders on all satellites and rescan since 11 MHz is enough that they can't be locked without doing this.

Without any kind of frequency counter, could I open up the LNB while it is installed and perhaps tune the LO while monitoring a known satellite transponder on my receiver to correct this?

You can try this, however, you need a NON conductive screwdriver to do this. Don't attempt it with a metal one.

 

[cyberham]

You can try this, however, you need a NON conductive screwdriver to do this. Don't attempt it with a metal one.

Good point. I think I may have a plastic one.

 

[a33]

Otherwise, when you can set your LOFs manually in your receiver, you can set the LOFs 11 MHz different. No problem.
And better than changing all individual frequencies.

I had a LNB once, that had a temperature-dependent LOF. I changed LOF values every spring and fall in my receiver.

Greetz,
A33

 

[cyberham]

Otherwise, you can set your LOFs manually in your receiver, you can set the LOFs 11 MHz different...

It's not possible to change the LNB LO frequency in my three receivers. You must choose from a fixed collection of LOs in a dropdown list. You can adjust yours in your receiver?

Update: I guess I can edit my LO manually in my Edision Mio4k+ but not in my GT Media receivers. I prefer not since I move my Edision among multiple dishes so I would need to change it on each satellite for different LNBs. Correcting at the LNB would be more convenient: one time fix.

 

[lost_mesa]

I adjusted the LO frequency of a Ku band LNB back around 1990. It was easy to do and pretty obvious what to turn, since there was only one thing that looked like an adjustment. It looked a bit like a screw. YMMV.

 

[a33]

You can adjust yours in your receiver?

Absolutely.
But alas, in the receivers that I own, it is not possible to set the "threshold" between high an low band.

 

[cyberham]

Absolutely.
But alas, in the receivers that I own, it is not possible to set the "threshold" between high an low band.

My Edision Mio4k+ does allow adjusting LO and the threshold. But first I'll try adjusting the LNB.

 

[Titanium]

There are two tuning slugs. Simple to tune with a non-metallic flat blade tool and a spectrum analyzer with signal generator. I forget which slugs are for high and low band, but recall that they are labeled.

If you don't have a 12G signal generator, use a known frequency narrow carrier and a SA or calibrated RTL-SDR tuned to the IF. The satellite ID is a good narrow signal (CW) and listed on the operator's bird specifications or licensing agency's grant.

Edit: Found this photo online.

 

[cyberham]

There are two tuning slugs. Simple to tune with a non-metallic flat blade tool and a spectrum analyzer with signal generator. I forget which slugs are for high and low band, but recall that they are labeled.

If you don't have a 12G signal generator, use a known frequency narrow carrier and a SA or calibrated RTL-SDR tuned to the IF. The satellite ID is a good narrow signal (CW) and listed on the operator's bird specifications or licensing agency's grant.

Haha. I have a voltmeter.

I will try adjusting a small amount, then run into the house to blind scan to see how much effect it had. I will intelligently repeat. This is how one improvises when one doesn't have a lab of equipment at their disposal. If I mess it up, that's OK. FTA is all an experiment.

 

[Titanium]

Surprised that you don't own an RTL-SDR. Best $35 you will ever spend...
www.nooelec.com/store/sdr/sdr-receivers.html

 

[cyberham]

Surprised that you don't own an RTL-SDR. Best $35 you will ever spend...
www.nooelec.com/store/sdr/sdr-receivers.html

Diverting...I've been on the edge many times for getting an SDR. I want to be able to record a complete overnight segment of the AM broadcast band to be able to listen to it in the morning hours with my coffee searching for DX. Seniors can't stay up all night tuning the radio live. Maybe I should take the plunge...

 

[cyberham]

Below from online. It may not be as simple as tuning. Mine is off by precisely 11 MHz as this mentions:

• Stability: The SNH-031 has a typical LO stability of +/-1 MHz and a maximum drift of +/-3 MHz. If your LNB is off by a significant amount (e.g., 11 MHz), it may indicate a failure or that it is near the end of its life, although, for some, this unit still performs well despite being off-frequency.

 

[lost_mesa]

I moved the LO 50 MHz! Not because it was broken but because it was made for a nonstandard 950 to 1400 MHz IF. I was changing my system to the more standard 950 to 1450 IF. Technology has changed a lot since then, so you might not have such a large range of adjustment.

 

[Titanium]

The stability range referred to warm-up and operational drift, i.e. thermal. Over the years, two problems haunted the Invacom LNB(f)s: 1. The feed throat cover quickly failed due to UV. 2. LO drift, which would happen even if it was NOS stored unused in temp/humidity control.

Several times I have re-tuned an Invacom 8+ MHz. Never swept the slugs to check for maximum range or roll-off, but 10 MHz adjustment is very doable.

 

[cyberham]

The final answer (for now...) is the SNH-031 has left the dish. The path of least resistance was to install a Geosatpro SL1PLL standard LNB. The universal gives me nothing extra at this location, the SL1PLL is MUCH lighter which makes my Stab rotator happier with the low voltage it receives through my long cable run, and I find PLL LNBs are superior in locking signals.

Maybe in future I'll get back to this Invacom or it may remain in my satellite museum along with my Geosatpro microHD receiver.