What are the consequences of this short run impedance mismatch?

[dragon48]

I'm using this 0.85-foot flat coax which allows me to fully close the balcony door over the cable.

https://www.amazon.com/dp/B099J66BWF

Thanks @GTR8000 for the suggestion, although I don't see it sucking yet


It's connected to 50 OHM SMA cables on both ends; the last end going into the antenna. The new setup is functional, and I don't notice worse reception or anything else wrong, but I just made the change. Anyway, as a matter of pure science, what exactly am I losing by connecting both ends of 50 OHM cabling with this 75 OHM cable? If it's worth throwing a little money at the problem, can somebody link me to an appropriate balun?

If it makes a difference for the answer, this is for receive only.

 

[buddrousa]

1. Is this Receive only
2. If this is Transmit and Receive what kinda power out of the transmitter
3. What is the frequencies used

 

[dragon48]

Receive only.

Radio Broadcast F.M., Shortwave, Marine and Weather Bands.

 

[ka3aaa]

isn't going to hurt a thing.

 

[doctordialtone]

Radio Broadcast F.M., Shortwave, Marine and Weather Bands.

No harm can be done in receive only mode.

 

[Ubbe]

I've measured that flex cable and another that looks more like a flattened coax and the flattened coax had lesser impact on the signal. Both creates havoc with impedance and attenuation but it's an easy solution and I use 3 of them for sat dish and one shortwave wire antenna, non critical signal levels. The flattened coax needs to be replaced after a while as mine wears out and loose almost all signal after some 500 times of open and closing a balcony door.

/Ubbe

 

[dragon48]

I've measured that flex cable and another that looks more like a flattened coax and the flattened coax had lesser impact on the signal. Both creates havoc with impedance and attenuation but it's an easy solution and I use 3 of them for sat dish and one shortwave wire antenna, non critical signal levels. The flattened coax needs to be replaced after a while as mine wears out and loose almost all signal after some 500 times of open and closing a balcony door.

/Ubbe

Ty - I'm not rich, but if my cable wears out on 500 days, I can afford another $7.99. I listened another 4-5 hours last night with the setup and no problems at all.

 

[dragon48]

I'm rekindling this thread with some info. I had previously just tested the differences with my ears, but delving deeper into the issue, shows I'm indeed losing something with the flat coax in the chain. First test:

Radio AOR 3000a
Frequency 162.475 MHz (Local NOAA).

With and without the flat coax, the station sounds exactly the same, however, without the flat coax in the chain, the radio shows 4 or 5 bars of reception, with a terminal shown signal strength of between E-F, but when I add the flat coax to the chain, the bars go down to 1 or 2 bars, with a terminal signal strength of between A-C. According to the manual, signal strengths are measured with the first 16 letters of the alphabet - A-P, with A being the lowest strength, and P being the highest. I repeated the experiment with an FM radio Station 107.1 MHZ, and without the flat coax in the chain, I get 5 bars of reception, with a terminal readout of F, and with the coax in the chain, I get 4 bars of reception and a terminal strength of E. With 105.9 MHz, and without the flat coax in the chain, I get 5 bars a terminal readout of F, and with the flat coax in the chain, I get 4 bars and a terminal readout of between D-E. This station also sounds exactly the same, with and without the flat coax in the chain.

I reseated and bypassed the coax several times and the differences remain. Also, the results are the same whether or not the door is closed over the flat coax.

Is the signal loss with the flat coax in the chain attributed to the additional connectors? I've got male to male RG6 connectors on each end of the flat coax, then SMA Male to F Female adapters connected to both of those ends; one end goes to the antenna, the other gets to my radio. If the signal loss is due to the connectors, is there a better way to do this?

Maybe @GTR8000 was correct and the flat coax cable to some extent sucks.

Again, I notice 0% of an audio change with both setups, but I would like to get the best possible signal with the balcony door fully closed. I don't always just listen to NOAA and FM radio, and am wondering whether with other, weaker signals, the addition of the flat coax will be noticeable.

 

[a417]

Is the signal loss with the flat coax in the chain attributed to the additional connectors?

Every additional connector will increase signal loss. I've always reterminated patch cables to avoid adaptors, it's worth the effort. Adaptors are great in a pinch, but long term usage they are another point of failure. If you're dealing with weak signals, additional adaptors can make them disappear entirely.

...and @GTR8000 is a wise man.

 

[dragon48]

Every additional connector will increase signal loss. I've always reterminated patch cables to avoid adaptors, it's worth the effort. Adaptors are great in a pinch, but long term usage they are another point of failure. If you're dealing with weak signals, additional adaptors can make them disappear entirely.

...and @GTR8000 is a wise man.

I've got far too much going on with my setup - BNC to BNC to SMA to SMA to SMA to SMA-to-SMA male to F Female adapter to Male-to-Male Coax adapter to the flat coax to SMA male to F Female adapter to SMA, to another Male-to-Male Coax adapter, to then, FINALLY to the antenna with the last SMA connection!

I did notice one thing with this and similar setups where I chain SMA cables together. With SMA male to female connections, if leave out the washers in-between the connectors, the signal is worse, so, tighter is better.

The start of my chain is necessary as the radio has a BNC connector and I'm using an SMA antenna. The other SMA components are to get enough length to get the antenna out of my apartment. Maybe I should redo all of this with a BNC to coax connector from the radio, then a long coax run to the inside of the balcony door, then add the flat coax, then a Male-to-Male Coax adapter, then to the antenna with the last SMA connection. Still adapters and points of failure, but I think this would be tighter.

BTW, is your avatar Dan Aykroyd?

 

[a417]

I've got far too much going on with my setup - BNC to BNC to SMA to SMA to SMA to SMA-to-SMA male to F Female adapter to Male-to-Male Coax adapter to the flat coax to SMA male to F Female adapter to SMA, to another Male-to-Male Coax adapter, to then, FINALLY to the antenna with the last SMA connection!

That's ridiculous. That's your signal loss right there. That sounds like about $80 in adaptors alone.

Your second plan seems to have less connectors, which when done appropriately will help alleviate your signal loss. Longer runs of good coax with the fewest adapters needed will be better.

If I were you, i'd do something like RG8/X with BNC male (for the radio) and F-Male (for the flat coax) and then another jumper with F-Male (flat coax) to SMA (for your antenna). You don't need adaptors if you terminate the appropriate wire here with appropriate ends. But you're not me, and I don't use flax coax.

...and no, it's Bob Hoskins.

 

[mmckenna]

I've got far too much going on with my setup - BNC to BNC to SMA to SMA to SMA to SMA-to-SMA male to F Female adapter to Male-to-Male Coax adapter to the flat coax to SMA male to F Female adapter to SMA, to another Male-to-Male Coax adapter, to then, FINALLY to the antenna with the last SMA connection!

Holy insertion loss, Batman!

 

[GTR8000]

...and @GTR8000 is a wise man.

I think you forgot three letters in that post...I'm usually being called a wiseass, not the first half of the word on its own. 🙃

 

[buddrousa]

@GTR8000
If you would care you can use my High School Graduation picture.

 

[dragon48]

The flat Coax cable indeed sucks! So, I haven't solved the root problem of how to close the door completely without degrading the signal too much, but I did learn a valuable lesson about signal loss.

I'm currently using this setup which gets me the best signal:

Thirty feet of 50 Ohm male to male BNC coax, with one BNC to SMA connector at the end of the chain, which connects to 10 feet of SMA cabling, going into an SMA antenna which is currently sitting on top of a balcony rail. The one tight conversion at the end of the chain does not degrade the signal at all, as I get the exact reception and signal indicators if I terminate the connection with a BNC antenna. My SMA antenna is more flexible and easier to ideally place, than a stock BNC telescoping antenna.

I'm currently listening to the local NOAA station - 162.475 MHz, and get 5 bars of reception indicators on the radio and a terminal signal strength of G. As soon as I add that stupid flat coax to the chain, the bars drop to 2, and the terminal signal strength drops to C!

With the coax leaving the door at the bottom, with the door mostly closing and touching the cable without putting pressure on it, there is a three-foot section of a 1/4-inch opening. For now, I'm more worried about bugs than making the AC work much harder and killing my electric bill. Unless I'm monitoring for something, I'll be bringing the antenna inside when not in use.

 

[Ubbe]

As soon as I add that stupid flat coax to the chain, the bars drop to 2, and the terminal signal strength drops to C!

I don't use mine, it is working much too bad, although it costs more. The flattened coax type attenuate at most 3dB-6dB depending of frequency, that's a half or one full signal bar. The flex cable type are only useable with terrestrial TV or FM radio signals that are already amplified at the antenna and can take a high attenuation level.

/Ubbe