RF components for TV and satellite installations

Hills TV/Satellite diplexer Model 19062

This device is intended to combine TV signals from a UHF or VHF antenna and L-band signals from a satellite LNB on to a single coaxial cable. Conversely, it can selectively divide signals from a coaxial cable to a satellite receiver and a TV receiver. From the photo, you can see that there is a dc path on the satellite side, so that the LNB can receive power from the satellite receiver. The important parameters for this type of device are the losses on each side and the amount of rejection provided from the other input port.

The network analyser plot of insertion loss vs frequency with the two ports overlaid is shown below:

From this plot, the insertion loss for TV signals is less than 0.5dB for VHF and up to about 1.5dB for UHF signals. The satellite side has less than 0.5dB loss from 1100MHz up. Indications are that this low loss figure will extend to 2400MHz. Rejection of the 'other' port is very good in both cases, and this device is a well-performing example of it's type.

WISI 2-way splitter Model DM12

This is a typical two way splitter although this one has diode steered dc paths from both split ports. The device covers the frequency band of 40MHz to 2050MHz and is effective for splitting both TV bands and satellite bands. The diodes in this case allow two receivers to be connected without the risk of feeding dc from one back to the other. However, if you do run two satellite receivers in this way, the one providing the higher dc voltage (e.g set to H polarisation or 18Vdc) will preside over the other. If both receivers are providing 18V there is no interaction, but if one receiver were set to select V polarisation (14Vdc) or was off, this would be ignored while the first receiver was still switched on.

The network analyser plot of insertion loss vs frequency and return loss vs frequency is shown below:

The insertion loss for either leg of the splitter is more or less 4dB as claimed across the band to 1600MHz apart from a minor resonance around 1050MHz. The loss is measured to one port while the other has a 75 ohm load connected. Return loss (the match) is very good below 250MHz, but worsens above this to be only 5dB at 1400MHz and higher. This does indicate we can expect an increased insertion loss above 1400MHz; the start of which can be seen on the plot. The other vital parameter for a splitter which I have not plotted, is the isolation. To test this, a signal is fed into one output port and measured at the other output port while the common port is loaded in 75 ohms. This parameter determines how much interaction occurs to one port from the other. Higher isolation is better. This splitter measured between 20dB and 25dB isolation over the full range 40MHz and 1800MHz, which is a very good result. Overall a useful splitter, very good isolation although insertion loss starts to increase above 1600MHz.

RSE 2-way satellite splitter Model A902

This is a two way splitter for satellite only covering the frequency band of 900MHz to 2050MHz. There is no dc path to either port so applications for this splitter are limited to situations where the satellite LNB is powered separately.

• Insertion Loss: 5dB at 900MHz to 7dB at 1.8GHz
• Return Loss: 6-8dB
• Isolation: 13dB at 900MHz to 18dB at 1.8GHz

Tests March 2012

2-way splitter ProLink Model SPHQ275F

This is a two way splitter covering the frequency band of 5MHz to 2050MHz with power pass from both ports. Following is a plot showing insertion loss in blue, return loss in red and isolation in green. The common port is loaded in 75 ohms for the isolation test.

The insertion loss for either leg of the splitter averages 4.1dB across the band to 1800MHz. The loss is measured to one port while the other has a 75 ohm load connected. Return loss (the match) is very good; being no worse than 15dB at any point. Isolation for this splitter is poor being no better than 10dB and as bad as 6dB in places. There will be interaction between loads because of this.

4-way splitter Signalmaster STM

This is a four way splitter covering the frequency band of 5MHz to 2400MHz with power pass from one port. Following is a plot showing insertion loss in blue, return loss in red and isolation in green. The common port and unused output ports are loaded in 75 ohms for the isolation test.

The insertion loss for either leg of the splitter averages 8.3dB across the band to 1800MHz. The loss is measured to one port while the others have 75 ohm loads connected. Return loss (the match) is very good; being no worse than 15dB at any point. Isolation for this splitter is very good and exceeds 20dB over the whole band to 1800MHz (which is the limitation of the analyser). Another check of interest is the isolation when not all ports are correctly loaded. In this case, removing the other output loads (leaving one port loaded) reduced the isolation to 14dB worst case, which is a good result. It means you can utilise the splitter with loads that are not very good matches and maintain a reasonable degree of isolation between them.

4-way splitter CHY

This is a four way splitter covering the frequency band of 5MHz to 2000MHz with power pass from one port. Following is a plot showing insertion loss in blue, return loss in red and isolation in green. The common port and unused output ports are loaded in 75 ohms for the isolation test.

The insertion loss for either leg of the splitter averages 8.6dB across the band to 1800MHz. The loss is measured to one port while the others have 75 ohm loads connected. Loss increases slightly to be 9-10dB above 1200MHz. Return loss (the match) is very good; being no worse than 15dB at any point. Isolation for this splitter is very good and exceeds 20dB over the whole band to 1800MHz (which is the limitation of the analyser). Another check of interest is the isolation when not all ports are correctly loaded. In this case, removing the other output loads (leaving one port loaded) reduced the isolation to 14dB worst case, which is a good result. It means you can utilise the splitter with loads that are not very good matches and maintain a reasonable degree of isolation between them. This model performs very similarly the Signalmaster above.

2-way splitter with Belling-Lee connectors

This is a two way splitter of no discernable parentage covering the frequency band of 5MHz to 900MHz (not covering satellite L-band). It is without power pass. Following is a plot showing insertion loss in blue, return loss in red and isolation in green. The common port is loaded in 75 ohms for the isolation test.

The splitter averages 4dB loss to 900MHz although it is increasing in loss from about 600MHz, reaching some 7dB. Return loss and isolation are surprisingly good for a model with these connectors. Isolation reduces down to around 10dB without a load on the common port.

3-way splitter Antronix model CMC2003BH-A

This is a three way splitter covering the frequency band of 5MHz to 1000MHz without power pass. Admittedly I had not heard of Antronix but they are a large supplier to the cable TV industry based in New Jersey, USA. Following is a plot which this time shows two insertion loss tests. In blue, loss is measured with all other ports loaded. Then, in green is the loss with the other two 'unloaded'. Return loss in in red as before.

The insertion loss for either leg of the splitter averages 5.3dB across the band to 1000MHz. The loss is measured to one port while the others have 75 ohm loads connected. Loss increases slightly from 820MHz to hit 6.8dB at 1GHz. Return loss (the match) is generally good although it does become worse than 10dB at a couple of points in UHF. Although I have been remiss in not plotting isolation, one can tell that it is high (good) because there is not much difference in the insertion loss when unused ports are left open.

10m of RG-6 coax

To illustrate the losses of this common domestic coax cable type, here is a plot to 1800MHz. Various manufacturers claim slightly differing figures but all are in the same ballpark.

This is for 10 metres. Different length? Just recalculate in dB proportions. Got 20m? Loss at 1GHz is 2 x 2.2dB, or 4.4dB.

Comment

for the splitters can they be used the other way around to combine signals and how much power can they take. thanks Gavin.