Railroad Base Scanner Indoor Antenna Question

[Ubbe]

The big difference between standard RG58 and RG6 are that the RG58 have a single braid that in many cases are not dense enough and will let interferences pass through it too easily form electronic equipments like network routers, LCD screens, all kind of computer things.

Impedance of coax and antennas for receive are secondary as scanners have problems to match those impedances anyhow.
https://forums.radioreference.com/u...6-bcd536hp-front-end-filter-measurements.html
https://forums.radioreference.com/u...-ubc780xlt-front-end-filter-measurements.html
https://forums.radioreference.com/whistler-scanners/371483-trx-2-front-end-filter-measurements.html

/Ubbe

 

[GROL]

Using 75 ohm coax instead of 50 ohm for receive is very insignificant. Not even worth the concern. The lower loss of RG-6 vs RG-58 more than overcomes any loss due to impedance mismatch. The dipole or the ground plane antenna will only present a 75 or 50 ohm match at only one frequency each. They are not broad band at all. I would expect the impendence will range from as little as a few ohms to a few hundred ohms over the 150 - 165 MHz for either antenna. In fact, the ground plane antenna will present a 75 ohm match at one frequency as well as it will be 50 ohms on another frequency. Opposite is true for the dipole. Usually when the impedance is stated as 50 or 75 ohms, it is in reference to a center frequency for the frequency range.

I have never checked, but I am curious what the impedance range is for a ground plane or dipole over a 15MHz range. I am usually checking antennas over a much narrower range. Usually not more than a few hundred KHz on HF or 4 MHZ range on 2 Meters. I'll have to try that out this weekend with my antenna analyzer. I know it will be a wide range of impedance, but not really sure exactly what.

 

[GROL]

The big difference between standard RG58 and RG6 are that the RG58 have a single braid that in many cases are not dense enough and will let interferences pass through it too easily form electronic equipments like network routers, LCD screens, all kind of computer things.

Impedance of coax and antennas for receive are secondary as scanners have problems to match those impedances anyhow.
https://forums.radioreference.com/u...6-bcd536hp-front-end-filter-measurements.html
https://forums.radioreference.com/u...-ubc780xlt-front-end-filter-measurements.html
https://forums.radioreference.com/whistler-scanners/371483-trx-2-front-end-filter-measurements.html

/Ubbe

Just be sure to buy 95% braid coax and it will be just fine. There is cheap stuff that is only 40%. Not enough difference to need double braid or double shielded coax to reject interference. Maybe only if you ran the RF coax parallel to and right against AC wiring. If you need to run parallel to AC wiring, try to get at least a few feet of separation. The only time I ever encountered a need for double shielding was a military application. It was used to insure nothing leaked out of the coax, not leak in.

 

[tkenny53]

When I used to rewire houses, Closets used to be one above the other. What I did was run the cable in a corner of a closet and up to the next one. Not knowing how many stories you have, see if you can do the same thing and run it to the attic space, then mount an decent base/mobile antenna there.

 

[Ubbe]

I sweept a GP 1/4 wave antenna for 150MHz and the result can be seen in the picture. The markers are for 10MHz steps down in frequency for the cut frequency (152MHz) but are the same going up.

/Ubbe

 

[GROL]

I sweept a GP 1/4 wave antenna for 150MHz and the result can be seen in the picture. The markers are for 10MHz steps down in frequency for the cut frequency (152MHz) but are the same going up.

/Ubbe

Nice!

It is not as wide a change in impedance as I thought it would be for 15MHz bandwidth, but I rarely look at antennas in the 150MHz range with an analyzer. In fact, I only use it to check for SWR on 2 meter antennas. I mainly use my analyzer in the HF bands where you see large changes of impedance when adjusting the length of an element.

The OP does not need to be concerned about using 75 ohm coax. It will not matter for his receive application. In fact, I have used 75 ohm coax for transmitting. I have a large surplus role of RG-6 and there are crimp on BNC connectors available for RG-6. It was a temporary installation until I found a really good deal on some military surplus HARRIS RF 50 foot RG-213 cables with BNC ends. $48 each I bought 6 cables before the guy ran out of them.

Thanks for posting your results.

 

[GROL]

Nice!

It is not as wide a change in impedance as I thought it would be for 15MHz bandwidth, but I rarely look at antennas in the 150MHz range with an analyzer. In fact, I only use it to check for SWR on 2 meter antennas. I mainly use my analyzer in the HF bands where you see large changes of impedance when adjusting the length of an element.

The OP does not need to be concerned about using 75 ohm coax. It will not matter for his receive application. In fact, I have used 75 ohm coax for transmitting. I have a large surplus role of RG-6 and there are crimp on BNC connectors available for RG-6. It was a temporary installation until I found a really good deal on some military surplus HARRIS RF 50 foot RG-213 cables with BNC ends. $48 each I bought 6 cables before the guy ran out of them.

Thanks for posting your results.

OOPs I meant to say I bought 2 of the RG-213 cables for $48 on each order. They were $24 for each cable. I don't recall the shipping, but it was less than $10. I bought three 2 cable orders over about 6 weeks time. If that eBay seller hadn't run out, I would have bought more.

 

[trp2525]

...there are crimp on BNC connectors available for RG-6...

I use compression-type BNC connectors (Radio Shack #278-033 or equivalent) on my RG-6 coax to avoid the use of any F-to-BNC adapters at my scanners. (These are like the compression-type F connectors used by the cable and satellite TV companies.) If anyone is interested here's a link to purchase 6 of the Radio Shack BNC compression connectors for RG-6 coax for $5.99 with FREE shipping included: https://www.ebay.com/itm/RADIO-SHAC...BNC-CONNECTOR-6-PACK-P-N-278-033/272755771926

 

[GROL]

I use compression-type BNC connectors (Radio Shack #278-033 or equivalent) on my RG-6 coax to avoid the use of any F-to-BNC adapters at my scanners. (These are like the compression-type F connectors used by the cable and satellite TV companies.) If anyone is interested here's a link to purchase 6 of the Radio Shack BNC compression connectors for RG-6 coax for $5.99 with FREE shipping included: https://www.ebay.com/itm/RADIO-SHAC...BNC-CONNECTOR-6-PACK-P-N-278-033/272755771926

Yep. The crimp on BNCs are nice on RG-6. They cost a bit more, but you can also find them at Lowes and Home Depot. You really should use the proper crimp tool for them, although I have been able to push them in with an open-end wrench that is snug around the back of the push in clamp. I don't recall the wrench size. But I had a couple failures doing that.

 

[Ubbe]

Isn't RG6 better than RG213 and easier to route as the dimension are less?
RG213 are only good for low frequencies with the single braid. RG214 are a better choise but it is more costly than a 1/2" coax with better specification.

Use the standard twist on F connector that's hard to fault as crimp on requires a costly crimp tool and it is easy to make mistakes when crimping with intermittent faults and strange signal losses. You'll probably need adapters to the antenna anyhow so why not use one at the scanner as well.

If you have a SWR of 2:1 and coax have 2dB attenuation the loss is 0.3dB and if the coax have 10dB attenuation the additional loss from SWR are 0.5dB. A 50 ohm impedance connected to a 75 ohm will get a SWR of 1.5:1

/Ubbe

 

[trp2525]

...The crimp on BNCs are nice on RG-6...You really should use the proper crimp tool for them...

...Use the standard twist on F connector that's hard to fault as crimp on requires a costly crimp tool...

FYI for those interested you can find the proper compression tool (used for the RG-6 BNC compression connectors that I referenced above in post #28) for just $5.99: https://www.ebay.com/itm/RadioShack-Compression-Connector-Tool-64-060-14/382136345087

Personally I don't see a major issue with terminating RG-6 coax with a high-quality compression F connector and then using an adapter (F to BNC, N, PL-259, etc.) to make your antenna and/or radio connection as I'm sure the insertion loss is minimal with a quality adapter. That being said I personally prefer to terminate my coax with the proper connectors to avoid the need for any adapters IF the proper connectors are available for the coax that I am using.

 

[GROL]

Isn't RG6 better than RG213 and easier to route as the dimension are less?
RG213 are only good for low frequencies with the single braid. RG214 are a better choise but it is more costly than a 1/2" coax with better specification.

Use the standard twist on F connector that's hard to fault as crimp on requires a costly crimp tool and it is easy to make mistakes when crimping with intermittent faults and strange signal losses. You'll probably need adapters to the antenna anyhow so why not use one at the scanner as well.

If you have a SWR of 2:1 and coax have 2dB attenuation the loss is 0.3dB and if the coax have 10dB attenuation the additional loss from SWR are 0.5dB. A 50 ohm impedance connected to a 75 ohm will get a SWR of 1.5:1

/Ubbe

RG-213 is only a bit thicker (0.405 inches) than RG-6 and it is very flexible. It has a 13 AWG stranded center conductor and a tight copper braid outer conductor. It has a recommended max frequency of 1GHz. Only 7dB loss per 100 feet at 1 GHz. Max power is about 250 watts at 1 GHz, and 2100 watts at 50 MHz.

I have deployed lots of the stuff in the military surrounded by all sorts of noise sources with no interference issues. Surrounded by a mobile TACAN, Mobile ATC RADAR, lots of 50KW and one 100KW generators, many ECUs and all sorts of other equipment in very close proximity. The RG-213 was used for an ATC Control Tower with frequencies in the 108-151 MHz and 225-400 MHz range. The control tower cable runs are 150 feet to the antennas and up the mast. Also used for HF radio as well.

The Mil Spec version is a very durable cable that I have seen survive the elements and much use. So I was very happy to find those 50 foot military surplus cables. They have Amphenol weatherproof BNC connectors on each end.

I have two cable runs of it on the ground behind my house that has been there for 2 years. I check it occasionally and did so last weekend when mowing the grass. I run over it with my lawn tractor frequently. Soft rubber tires don't hurt it on the ground. When I checked it last weekend, the jacket is still very pliable and not hardened at all. When wiped clean it appears like new cable.

 

[GROL]

RG-213 is only a bit thicker (0.405 inches) than RG-6 and it is very flexible. It has a 13 AWG stranded center conductor and a tight copper braid outer conductor. It has a recommended max frequency of 1GHz. Only 7dB loss per 100 feet at 1 GHz. Max power is about 250 watts at 1 GHz, and 2100 watts at 50 MHz.

I have deployed lots of the stuff in the military surrounded by all sorts of noise sources with no interference issues. Surrounded by a mobile TACAN, Mobile ATC RADAR, lots of 50KW and one 100KW generators, many ECUs and all sorts of other equipment in very close proximity. The RG-213 was used for an ATC Control Tower with frequencies in the 108-151 MHz and 225-400 MHz range. The control tower cable runs are 150 feet to the antennas and up the mast. Also used for HF radio as well.

The Mil Spec version is a very durable cable that I have seen survive the elements and much use. So I was very happy to find those 50 foot military surplus cables. They have Amphenol weatherproof BNC connectors on each end.

I have two cable runs of it on the ground behind my house that has been there for 2 years. I check it occasionally and did so last weekend when mowing the grass. I run over it with my lawn tractor frequently. Soft rubber tires don't hurt it on the ground. When I checked it last weekend, the jacket is still very pliable and not hardened at all. When wiped clean it appears like new cable.

And I forgot about the cable for the obstruction lights on the antenna towers. They were run along side the RG-213 cables going to the antennas. 120 volts. 60Hz. No interference issues.

 

[GROL]

FYI for those interested you can find the proper compression tool (used for the RG-6 BNC compression connectors that I referenced above in post #28) for just $5.99: https://www.ebay.com/itm/RadioShack-Compression-Connector-Tool-64-060-14/382136345087

Personally I don't see a major issue with terminating RG-6 coax with a high-quality compression F connector and then using an adapter (F to BNC, N, PL-259, etc.) to make your antenna and/or radio connection as I'm sure the insertion loss is minimal with a quality adapter. That being said I personally prefer to terminate my coax with the proper connectors to avoid the need for any adapters IF the proper connectors are available for the coax that I am using.

Nice find on the compression tool. I may order a spare. I paid about $15 for mine. With the compression tool it is very easy to put the compression connectors on and they grip the cable really tight. You really need the compression tool to get them on straight and fully compressed.

 

[cbehr91]

The big difference between standard RG58 and RG6 are that the RG58 have a single braid that in many cases are not dense enough and will let interferences pass through it too easily form electronic equipments like network routers, LCD screens, all kind of computer things.

Impedance of coax and antennas for receive are secondary as scanners have problems to match those impedances anyhow.
https://forums.radioreference.com/u...6-bcd536hp-front-end-filter-measurements.html
https://forums.radioreference.com/u...-ubc780xlt-front-end-filter-measurements.html
https://forums.radioreference.com/whistler-scanners/371483-trx-2-front-end-filter-measurements.html

/Ubbe

If you ever can do sweeps of the 125AT and the SDS100 I'd be really curious to see their results.

 

[Ubbe]

If you ever can do sweeps of the 125AT and the SDS100 I'd be really curious to see their results.

They would probably be more or less the same. Uniden doesn't re-design anything if they don't need to.

But the SDS100 would probably have needed much tigher and many more filters to handle an inteference prone SDR based receiver. If they had opted for varicap filters, like in professional radios, they might have been closer to a winner.

/Ubbe