Rabbit73, looks like you have a good collection of equipment for portable testing.
Having a near field view over open water helps with signal reception. Quote:
Quote:
Quote:
As you know, a lab grade antenna range is implemented in such a way to minimize all reflections that could be received in the main beam or sidelobes of the antenna under evaluation. Quote:
Quote:
General comment: All measurements have limits in accuracy. For most TV reception purposes, the measurements taken with less than optimum conditions may be satisfactory. In comparative testing, if there variables that one cannot control. Some form of averaging to wash out the variability can be helpful. In the case of systems receiving signals that vary with time, then time averaging can reduce the errors. If long enough time and enough samples are averaged for each system under test, then errors in measurement can be reduced. =========================== Quote:
However, the preamps may behave slightly different when connected to an actual receiving antenna with different transmission line and no splitter. In many case, this difference could be small enough to not matter to the individual performing the test. . |
Quote:
My wife supported my experiments, so I was able to collect the equipment I needed to solve reception problems. Quote:
Quote:
Quote:
Kent Britain, WA5VJB, creator of the Cheap Yagi, would place the antennas at ground level to minimize ground reflections during antenna shootouts. I tried that with indoor antenna tests. The results were consistent with results at 3 ft above the floor, but the signals were about 20 dB weaker on the floor (concrete slab covered with carpet). http://www.wa5vjb.com/references/Ant...0Notes-keb.pdf WA5VJB Antenna Measuring Notes, Extract Kent Britain WA5VJB (Written for Scatterpoint issue 1-2000 updated Sept 2006) Quote:
http://forum.tvfool.com/attachment.p...1&d=1495302313 http://forum.tvfool.com/attachment.p...2&d=1495302363 Quote:
Quote:
_____________________________ Happy Thanksgiving! Hope you are staying safe. Best regards, rabbit73 |
Quote:
Thanks for the .pdf, interesting read. Wonder how you use the BT double sideband Modulator? Do you inject a tone to provide a pair of CW signals, or add a DTV baseband. or something else? Quote:
. |
5 Attachment(s)
Quote:
My use is very simple. I don't have a UHF signal generator, so I use the NTSC video carrier of the modulator as a constant strength test signal. All I have to do is select an output channel on the Agile Modulator and tune my signal level meter or SDR to that frequency. It isn't necessary to modulate the carrier, the video carrier exists without video or audio input. http://forum.tvfool.com/attachment.p...1&d=1606500200 For VHF, I use a more sophisticated (and expensive) source; I generate an ATSC 1.0 carrier with my Thor Petit Modulator. http://forum.tvfool.com/attachment.p...3&d=1606503206 http://forum.tvfool.com/attachment.p...8&d=1606517223 http://forum.tvfool.com/attachment.p...9&d=1606518082 Testing the Thor Petit HDMI RF MODULATOR https://www.avsforum.com/threads/tes...lator.3095882/ |
Quote:
Not that it would be a serious problem for most antenna testing; Being a double sideband modulator, doesn't the NTSC video carrier show up twice in the spectrum? Quote:
. |
4 Attachment(s)
Quote:
http://forum.tvfool.com/attachment.p...1&d=1502665287 http://forum.tvfool.com/attachment.p...4&d=1606507557 Quote:
The video carrier is more precise; the ATSC signal is much wider and not always flat. So, where do you measure the ATSC Carrier when it isn't flat? My SLM takes an average of many readings when it scans the whole ATSC channel, but can measure the NTSC video carrier more exactly. With the SDR, I can select the measurement frequency at any place on the ATSC channel. http://forum.tvfool.com/attachment.p...5&d=1606508676 http://forum.tvfool.com/attachment.p...6&d=1606508775 http://forum.tvfool.com/attachment.p...7&d=1606516308 |
Thanks for the images.
Looks like displays from three different STL-SDR units, that is if the RTLSDR Scanner is running on one of the lower cost devices? When comparing the SDRplay and the Airspy, noticed the noise spectrum on the lower frequency side of Channel 3 is different for each. Specifically, the noise is increasing near lower edge of Ch3 for the SDRplay, for the Airspy decreases a bit near lower edge of Ch 3. Wonder if that reoccurs, repeatable? . |
1 Attachment(s)
Quote:
1. RTL-SDR.COM V3 dongle with free open-source Scanner software from GitHub 2. SDRplay RSP1A SDR with SDRuno software 3. Airspy R2 SDR with Spectrum Spy software that is included with the SDR# (SDRsharp) software download Quote:
1. The noise floor is not constant on VHF, especially VHF-Low; the scans were done at different times 2. The RSP1A with the SDRuno software is limited to a useful bandwidth of about 8 MHz; each side falls off pretty fast. The Airspy R2 with the Spectrum Spy software has an extremely wide bandwidth for a scan only limited to the full bandwidth of the R2. 3. The bandwidth of the antenna http://forum.tvfool.com/attachment.p...0&d=1606523160 |
Quote:
Quote:
Can the Airspy not scan & display a narrow 8-10 MHz region like the RSP1? When the RSP1 scans from say 45 MHz to 80 MHz, does the spectrum look like the Airspy R2 spectrum at the lower part of Channe 3? . |
6 Attachment(s)
Quote:
http://forum.tvfool.com/attachment.p...1&d=1606528894 R2 and Spectrum Spy at 10 MHz width: http://forum.tvfool.com/attachment.p...2&d=1606533033 Quote:
50 MHz width with RSP1A and RSP Spectrum Analyser: http://forum.tvfool.com/attachment.p...4&d=1606535050 I don't actually have an RF channel 3 in this area, or any 2-6 channel. That is why I bought the Thor modulator to simulate an RF 3 ATSC channel. I have been studying the affect that a high noise level has on the reception of VHF-Low channels. I first became interested in that project while trying to help a Canadian receive RF 2 and 4. I thought a CH3 folded dipole had a chance of receiving both. He was having no luck using an FM folded dipole of twinlead with 30 gauge conductors. I encouraged him to make a CH3 FD with larger diameter conductors, but he seemed unwilling to do it. I suspected that he had sufficient signal strength, but a high noise level. He was able to receive 9 OK. http://forum.tvfool.com/attachment.p...8&d=1606575802 http://forum.tvfool.com/attachment.p...5&d=1606574455 http://forum.tvfool.com/attachment.p...7&d=1606574746 I have two CH3 folded dipoles. I have one connected to the output of the Thor modulator. The other is connected to my SDR or a TV. It picks up the CH3 ATSC signal from the Thor modulator as if it were an OTA signal AND the ambient noise. This tells me how much stronger a VHF-Low signal needs to be for a sufficient SNR above the ambient noise. If you want a specific test done, I could set it up over the weekend. I don't keep the CH3 folded dipoles set up in my room. I would need to know exactly what test you want me to do. I could try to do 45 to 80 with all three SDRs, but it would require both CH3 folded dipoles to pick up the ambient noise. |
Quote:
Quote:
Quote:
Appreciate the offer, but not necessary. Your several images in this thread provide a fairly good idea of what can be expected from the RTL-SDR devices. ----------------------- One of the specific tests planned in KY: To determine if the 3rd order IMD from a broadcast station can be seen on one of these devices. The station IMD3 is strongest very near the edges 6 MHz spread. However, those edges are also where the SDR-RTL internal IMD may be highest. Therefore, it may be difficult to see low level station IMD with such devices. Another requirement for such an observation is for the broadcast station to be fairly well isolated from any other stations and have a high S/N ratio (in some case 50 dB or more). This condition may not be met in populated areas (cities, etc). There is a PBS station in rural KY that meets such criteria. ------------------------ Appreciate the patience, tests, and and images you have displayed in this thread and others. . |
All times are GMT. The time now is 5:05 AM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © TV Fool, LLC