Use satellite hookup for Ham antenna?

[Philip Jones]

Hi fellow Airstreamers,

I would like a simple way of passing the signal for a VHF/UHF antenna into my airstream. I was wondering if I could use my unused satellite TV connection on the outside of the Airstream for the coax from the antenna to avoid having to pass another coax cable through a window or vent.

I think the impedance of the satellite coax cable is 75 ohm rather than 50 ohm. But that should be Ok despite the losses that will ensue.

Has anyone hooked up an antenna to the satellite connection? I will also have to find where the satellite connection hookup enters the Airstream. The regular cable connection is easy to see. Thanks for any help.

[rmkrum]

The ‘F-type’ connectors and the existing cheap 75 ohm cable are not going to work with real well with a transmitter. There will be a rather high SWR and a lot of RF loss and leakage. It’s not going to be ‘OK’ in my opinion. Better to “do it right” with proper cable and connectors designed for VHF/UHF use.

I used my rooftop solar combiner box to get my 52 ohm low-loss RG-8 sized VHF/UHF cable to the roof. The antenna is clamped to the side of one of the solar panel support brackets. The main unit of the FT-857 is in the wardrobe closet under the combiner box. Very low SWR and a tidy install.

The head unit and speaker is on the desk at the rear of my AS and the extender cables were fished under the kitchen cabinets and wet bath. That was the hard part. There are also two feed-through connectors from the wardrobe into the outside refrigerator compartment. If I want to run HF, I can connect an antenna by opening the refrigerator compartment door.

[Philip Jones]

Thanks for your detailed reply! I guess I will need to re-think this plan... Just seemed too easy to use the existing hardware, I guess

My solar combiner is a later-model (2017) one, and I don’t think I can route cable through it, so perhaps I will use the fridge vent to route the cable.

[Al and Missy]

Originally Posted by rmkrum

The ‘F-type’ connectors and the existing cheap 75 ohm cable are not going to work with real well with a transmitter. There will be a rather high SWR and a lot of RF loss and leakage. It’s not going to be ‘OK’ in my opinion. Better to “do it right” with proper cable and connectors designed for VHF/UHF use.

I used my rooftop solar combiner box to get my 52 ohm low-loss RG-8 sized VHF/UHF cable to the roof. The antenna is clamped to the side of one of the solar panel support brackets. The main unit of the FT-857 is in the wardrobe closet under the combiner box. Very low SWR and a tidy install.

The head unit and speaker is on the desk at the rear of my AS and the extender cables were fished under the kitchen cabinets and wet bath. That was the hard part. There are also two feed-through connectors from the wardrobe into the outside refrigerator compartment. If I want to run HF, I can connect an antenna by opening the refrigerator compartment door.

Rich,


I'm going to offer a contrary opinion, but preface it with the fact that I have no idea what cable Airstream is using. Older trailers may have RG-59 for the cable TV line, newer ones should have RG-6 for the satellite run. The currently available satellite capable RG-6 is good up to 1.2 GHz and has a loss of 2dB at 100 MHz. The commonly used RG-8X has a loss of 3 dB at 100 MHz. The SWR of a 50 ohm load on a 75 ohm cable is 75/50 = 1.5:1. I'd venture a guess that the use of RG-6 including mismatch loss at 100 MHz would have a loss equivalent to RG-8X. One would have to go to RG-8 or maybe even RG-213 to improve on the performance of RG-6. The dimensions and construction of RG-6 are equivalent to RG-58 or maybe even RG-8X so I wouldn't be concerned about low power (<100W) transmit operation.



One must also consider that the quoted specs are for 100 feet. With a run probably less than 25 feet in the Airstream application, the losses would appear to be negligible, less than 0.5 dB, at least at 100 MHz.



I've never done it, but if I were the OP, I'd probably try it.


Al

[rmkrum]

The RG-59 vs the RG-6 (And maybe if RG-6 quad shield) problem is why I wouldn’t try it personally. Who knows how badly the factory ran the cable, or where the joints are?

I’d rather do new cable...and proper connectors for ham radio gear and antennas is another possible issue.