On VHF, where the ambient noise level is higher than -106 dBm, the system noise figure calculation and the lower NF of the preamp become irrelevant because they are based on the thermal noise floor of -106 dBm. Since the NF of a good preamp is less than the NF of a tuner, the system noise figure is improved according to the Friis formula because the preamp is at the headend of the system. On UHF, a preamp will amplify a signal, amplify the noise, and add its own noise. It looks pretty crowded in that attic must have taken a while to do the setup. Thank you for the interesting report from WA. Any additional comments re are welcome, of course.Įdit: Added a pic of the current attic setup (DB4e and 30-2476) and more FM radio info. I recall rabbit had some explanation on why pre-amps don't help on VHF, so I will look for it. I have the Hi-V into the pre-amp still, but it's for convenience and not necessity. I've mostly been able to get KCTS now from Seattle, but I put up the big Stellar 30-2476 in the attic to make it (mostly) reliable. I have 3 LOS FM stations from Capitol Peak, at about 18 miles, one of which is a whopping 70kW. It definitely isolates Hi-V but not FM radio. So, I will filter VHF on the UHF input next time. It is now, but it does little for the 3rd strongest station there (88.1). That was a bit of a shock and my FM trap wasn't in. What I found most interesting is that the classic CM 7777 pre-amp was passing FM radio on the UHF side even with the VHF side trapped.
I tried 3 different pre-amps and various sets of attenuators. It definitely helps UHF quite a bit, however. After many different tweaks, I've pretty much concluded that pre-amps on Hi-V are of little to no benefit, at least for the short 6' cable runs I have to my tuners. I was up in WA again this past weekend for the 4th and did all kinds of things to improve Hi-V reception. 106 dBm Thermal Noise + 6 dB tuner NF + 15 dB SNR = -85 dBm Simplified calculation of minimum required signal:
This means that dropout will be at a level higher than -85 dBm because the VHF signal needs to be stronger to have sufficient SNR above the higher VHF noise level. The ambient noise level on VHF is higher than the Thermal Noise Floor of -106 dBm for a 6 MHz channel. The dropout test should be done with a UHF channel. It's the difference between the SDR reading and -85 dBm. If I have any doubts about the correction factor, I only need a variable attenuator for a double check.Įven if you don't have a signal level meter, you can calculate the correction factor with an attenuator and dropout at about -100 dBm (uncorrected) on the SDR. Now that I know the correction factor, I don't need my signal level meter. Signal Strength, Signal-to-Noise Ratio and Other Related Issues in DTV If you are using a preamp, dropout might be at a lower dBm value (more likely on UHF than on VHF) if the Noise Figure of the preamp is less than the Noise Figure of the tuner. Information submitted to us is only available to employees managing this information for purposes of contacting you or sending you emails based on your request for information and to contracted service providers for purposes of providing services relating to our communications with you.Most tuners dropout around -85 dBm close enough. We will never share, sell, or rent individual personal information with anyone without your advance permission or unless ordered by a court of law. We use security measures to protect against the loss, misuse and alteration of data used by our system. We respect your time and attention by controlling the frequency of our mailings. If you received a mailing from us, (a) your email address is either listed with us as someone who has expressly shared this address for the purpose of receiving information in the future ("opt-in"), or (b) you have registered or purchased or otherwise have an existing relationship with us. We have created this email privacy policy to demonstrate our firm commitment to your privacy and the protection of your information. NO REFUNDS WILL BE GIVEN ON ABANDONED PROPERTY. ANY ITEM REMAINING AFTER JANUWILL BE CONSIDERED ABANDONED PROPERTY. ALL ITEMS MUST BE PICKED UP ON ON THE DAYS SPECIFIED ABOVE. No party, other than Bidilla, Inc is authorized to release any item sold at this auction. Preview appointments can be made email at PICKUP: All items are to be picked up by the buyer on January 12, January 13, OR January 20 2022, from 9 AM CT to 2 PM CT, after full payment of the invoice and verification of funds. Preview day is Januwith a time prearranged with Bidilla, Inc in advance.
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