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Background: Sort of following up a previous thread of mine, I have been experimenting with an amplified indoor "Digital TV" antenna.* This particular design consists of a passive flat panel approx. 8.7" tall x 9.7" wide x ~0.1" thick, which is directly wired to a ~16 ft. long thin (3mm dia. / ~0.11" dia.) coax cable terminated in a std. TV aerial (RG-59) type connector. That plug connects (threads on to) to a TV aerial female jack on the body of a small amplifier module. Power is supplied by a USB cable that directly (no plug) feeds the amplifier. No power is fed to the antenna itself (zero voltage at the TV aerial jack - I checked with a digital multimeter.) The amplifier is said to feature an "improved" LTE filter to chop off the no longer used-for-TV upper UHF band. I'd have to go back and check, but I believe the amplifier gain is 20 dB. The amplifier output is connected to the TV by a short (~2.5 ft.) similarly thin thin coax cable. I've no worries about the output cable, with the amp gain ahead of it, but, I'd think one would want to minimize losses ahead of the amp. (Presently this rig picks up a close station better than my outdoor antenna*, but the indoor rig doesn't pick up medium distance stations that another indoor antenna does -- but that 2nd indoor antenna seems to have more problems with intermittent LTE interference. (#2 is a bit older and not advertised as having LTE filtering.)

SO...! While it might not make much difference, I am wondering if I could:

Scenario 1 - splice new copper braid / shield RG 59 or better 75 ohm coax cable (I have a lot of it) to the output of the antenna to link it to the amplifier. This would shorten the "thin" cable coming out of the antenna to 2" or so. BUT, will this potentially cause reflections at the splice and / or how would one avoid such?**

Scenario 2a - Shorten the thin cable between the antenna and amp to ~2", either by a splice that chops out most of the existing cable, OR, if I get brave...

Scenario 2b - Crack open the amplifier and wire the now 2" long thin cable directly to the solder points inside the case. Either way, to make up the increased length then needed from the amp to the TV I can use a std. female-to-female TV aerial connector and whatever length is needed of RG 59 or better cable with male ends on it to reach the TV.

"2a" again leaves me with a bit of a worry about the splice. In either 2a or 2b I'd have to extend the power cable - no problem!

2a and 2b allow me a lot of flexibility in remote mounting (distance to) of the antenna, including going up into the attic above the TV.

** The whole subject of RF transmission line impedance and reflection is "really wild" to a relative novice like me. This article

https://www.emisoftware.com/blogs/cabling-affects-emi-unexpected-ways/#:~:text=As%20cable%20length%20increases%20from,the%20impedance%20is%20very%20high.

makes me wonder how it would not be a matter of luck, or bad luck, that one or more TV stations one was trying to receive would not fall into a null or (just as bad?) a peak?

*The (presently unamplified) outdoor antenna gives me grief sometimes on strong signals too. I may need to put a LTE filter on it, between the antenna and the amplifier (which doesn't have LTE filtering) I had up there / would try again up there. A springtime project...!

1 posted on 01/23/2023 7:42:41 PM PST by Paul R.
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To: Paul R.

Oh, good grief - I forgot to change the title to “Monday”!

(Started this question last night.)


2 posted on 01/23/2023 7:43:42 PM PST by Paul R. (You know your pullets are dumb if they don't recognize a half Whopper as food!)
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To: Paul R.

Yes!


3 posted on 01/23/2023 7:44:08 PM PST by Repeal The 17th (Get out of the matrix and get a real life.)
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To: Paul R.

https://www.bing.com/search?q=mixing+cable+impedences&cvid=a8bc3a31eead48e08f852290f8ee1c79&aqs=edge..69i57.16339j0j9&FORM=ANAB01&PC=U531


7 posted on 01/23/2023 7:48:08 PM PST by TexasGator (!!!)
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To: Paul R.

I always got my best gain with 300 Ohm flat wire cable, and resent the day it started going to 75 Ohm coax. More interference, but more signal, too.

I have never found an RF amplifier that did much for the signal. Back in the pre-cable days, my father employed a device from Jerrold known as a trap, which was used to improve weak signals close to strong ones. In our case, Channel 8 (WNHC-ABC, New Haven) was overpowering channel 9 (WOR-Ind, New York) and Channel 7 (WABC-ABC, New York). That sometimes worked depending on atmospheric conditions, but it didn’t really strengthen the signal, only made the existing signal more useable.


11 posted on 01/23/2023 7:56:07 PM PST by Dr. Sivana (But yet the Son of man, when he cometh, shall he find, think you, faith on earth? (Luke 18:8))
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To: Paul R.

You can donit but at these frequencies you’re not going to see much improvement and depending on your splices could make it worse.


12 posted on 01/23/2023 8:23:51 PM PST by bigbob
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To: Paul R.

As long as both cables are 75 Ohm you will have a good match, but you also have to use correct connectors, usually F series for RG-59 coax or RG-6 (low loss, a little bigger coax). RG-6 IIRC take a little different connector to match the larger wire diameter, but has the same F-series end.

Coax impedance is determined by relationship of size of the center wire in comparison to the ground shield surrounding it. As long as the size ratio stays the same, you can have a smaller or larger coax that is still 75 Ohm. That’s why you need the proper connectors to keep that relationship at the junction so there is no change in impedance at the junction.


15 posted on 01/23/2023 8:38:44 PM PST by E.Allen
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To: Paul R.

Throw out the RG59, buy new cable - RG 6/11 - use quality connectors and just do your splice/run.

Should be good, assuming you know how to do a coax connector without noise...


19 posted on 01/23/2023 9:38:10 PM PST by logi_cal869 (-cynicus the "concern troll" a/o 10/03/2018 /!i!! &@$%&*(@ -)
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To: Paul R.

Here are flat 75 ohm cable and an adapter.
https://www.amazon.com/300-ohm-twin-lead/s?k=300+ohm+twin+lead


20 posted on 01/23/2023 10:20:53 PM PST by minnesota_bound (Need more money to buy everything now)
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