LNBF really drifting badly

[wejones]

Yesterday, I was surfing through AMC3 looking for changes in the PBS lineup. Since my big dish was on another sat, I used the 90CM, and connected the passthru of my lifetime to one of my DCII receivers. I first tuned in the Fortec to the Montanna PBS at 12145 MHz. Then I switched to my DCII receiver, and started browsing through the channels to see if there was anything new or missing. After a short run through the channels, I found what I THOUGHT was a new channel. It had an IF of 1394.25, and it had some interesting programming on it. Thinking that I had a new channel to report, I did the conversion to downlink freq, ie 10750+1394.25= 12144.25 . Then a light went off in my head, and I realized that this couldn't be correct. Ie if I'm receiving the Montanna PBS signal at 12145, I CAN'T be receiving a DCII channel at 12144. Then I remembered, that the KUL1 lnbf on my 90CM dish has been off by about 2 MHz. I checked the freq offset on the DCII receiver, and it was about 2.5 MHz off, so I THOUGHT that this was "normal", and the Montanna PBS channel I had running on the Fortec off the same signal at the same time was actually tuned in with a 12143 MHz freq because of the 2 MHz that I thought I was off.
Well, to make a long story shorter, after fooling with the thing for a couple hours, I finally identified the channel I was looking at. It was the Annenberg CPB channel, at 12151 !!!! So I switched to that channel on my DCII receiver, let it run a while, and checked the frequency offset. It was off by almost 5 MHz!!! Ie the 2.5 MHz I had noticed when first looking at the 1394.25, was a positive 2.5, and I remembered that normally I had a negative 2 MHz offset, so I was really looking at an error of 2 + 2.5 = 4.5 MHz.
This morning, I looked at the DCII signal again, and it was still off by 4 MHz on the 12151 signal. I thought that perhaps this was temperature related, so I found an old glove, and went out and put it loosely over the LNBF, then came back in, and watched the freq offset. I've been watching for about a half hour now, the offset has been slowly, but steadily dropping. As I type it has dropped to -3.375, and I think it is still dropping.
I'm thinking about trying to make a foam insulation jacket for the thing, to keep the temperature a bit more stable, because there probably isn't enough heat generated within the LNBF to match what is lost from a loose fitting glove. However, I guess what I really need to do is upgrade to a higher quality LNBF that doesn't drift so much with temperature changes. Ie if it drifts this much when the temperature is only around 15 deg F, I can't imagine how much it will be off when the temp gets down to -15.

Anyway, if anyone is having problems finding narrow signals, you might consider that your lnbf is drifting, because at least this KUL1 thing seems to drift quite a bit.

[Sadoun]

Bill

All consumer level LNBFs will drift. See also the Invacom specs http://sadoun.com/Sat/Products/Invacom/Single.pdf

The drift is +/-3 Mhz. At 15F, the LNBF will drift to the max.

If you are looking for a commercial level stable LNBF, then prepare to spend $$$ for it.

[wejones]

Originally Posted by Sadoun

Bill

All consumer level LNBFs will drift. See also the Invacom specs http://sadoun.com/Sat/Products/Invacom/Single.pdf

The drift is +/-3 Mhz. At 15F, the LNBF will drift to the max.

If you are looking for a commercial level stable LNBF, then prepare to spend $$$ for it.

I understand that, but 4.5 MHz is pretty bad for even a consumer LNBF.
I guess I was used to, and comparing to the performance of the consumer level LNBs I've had on my big dish. My old Cal Amp lnb, which was poor for even consumer level drifted as much as maybe 1.5 to 2 Mhz at times, but the drift was centered around the correct frequency, and it was usually off by less than 1.5 Mhz. My current big dish LNB, which is still consumer level, ie one of the cheaper Norsat LNBs, is usually within 1 MHz of the correct freq. It's rated at something like +/- 750 KHz.

This KUL1 was off by 2MHz out of the box, and seems to be temperature dependent. The KUL1 is rated at +/- 1 MHz, but that is at 25 deg C. It's actually fairly stable at whatever temperature it's at, ie it doesn't really "drift" so much as it's freq changes with temperature. For DVB signals, I can deal with it being off freq by altering the LO freq in the receiver setup, but it makes locking on DCII signals difficult because the frequency is determined by the VCT not by the user, and DCII receivers don't have a LO setting in the setup. High SR signals lock in pretty quickly, but it can take 5 minutes for narrow SR signals to be found, and sometimes it finds the wrong signal.

But you're probably right about the you get what you pay for, as I think I paid more for even my cheapest big dish LNB than I did for this little LNBF. I've never figured out why an LNB should be more expensive than an LNBF, but they seem to be.

Part of my problem is that while there seems to be a fairly good selection of LNBFs out there, most of them seem to be universal, and since I also do DCII, I need a standard, and it seems like I'm pretty much limited to either the KUL1 or the Invacom. I'm curious with respect to whether anyone knows of any other "standard" lnbfs that have good frequency accuracy and stability? I probably could just get another KUL1, and it would probably be better than the one I have, but I think that I'm going to give the Invacom a try.