Anyone have any experience using 75 ohm CATV cable on 70 cm?
Mike KA5SMA
I have used the 1/2 " hardline type with disk type dielecrtric for several years. A 1/4 wave of brass hobby tubing driven over the copper center conductor and soldered at both ends solves the 50/75 transition problem. Used the Hardline splice connector with homade made mechanical fitting adapted to a N type female connector. The larger sizes are available as remenants on a large spool very cheep!
Art, KC6UQH
From: "Mike Miller" mmiller@nctc.com To: amsat-bb@amsat.org Sent: Monday, May 21, 2007 5:35 PM Subject: [amsat-bb] 75 ohm CATV Cable on 70 cm
Anyone have any experience using 75 ohm CATV cable on 70 cm?
Mike KA5SMA _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
----- Original Message ----- From: "kc6uqh" kc6uqh@cox.net To: "Mike Miller" mmiller@nctc.com; amsat-bb@amsat.org Sent: Tuesday, May 22, 2007 7:46 AM Subject: [amsat-bb] Re: 75 ohm CATV Cable on 70 cm
I have used the 1/2 " hardline type with disk type dielecrtric for several years. A 1/4 wave of brass hobby tubing driven over the copper center conductor and soldered at both ends solves the 50/75 transition problem.
Art, KC6UQH
Hi Art, KC6UQH
If the diameter of your 1/4 electrical wave long of brass hobby tubing driven over the copper center conductor changes the impedance of this cable section from 75 ohm to SQR( 50 * 75) = 61 ohm it is a good idea.
Best 73" de
i8CVS Domenico
...yes, I tryed that on my 2nd QTH because my experience with 100ft of RG213 was very bad on UHF.
It was Sunday - no chance to buy something better.. so I decided to replace the RG213 with 75 Ohm TV cable.
Well, the receiving-difference it was spectacular! With 75Ohm cable it was possible to hear Loud & clear the FO-29 downlink, with RG-213 not good enough! The same I noticed with other Satellites and weak signal ground stations.
Later, after few weeks I replaced the 75 Ohm cable with AirCom+. Nothing changed between 75 Ohm TV and AirCom+ in the receiving! Absolutely equal receiving between the two cables, even if the AirCom+ was "10 times" much more expensive cable!
But in transmittion, it's obvious that the 75 Ohm cable has problem. It is not the mismatch (SWR 1.5) but this cable probably can not drive output Power bigger than 5-10 Watts. I confirmed that with 2-3 RIGs and several type of antennas. If you have output Power bigger than 10 Watts, is possible the RIG to decrease the Power output (ALC action? protection? I don't know!)a few seconds after PTT's press. (I'm talking always for UHF band).
So, from my experience I believe that the 75 Ohm is excellent in case you need a separate cable from UHF-LNA output upto the Shack. I noticed that the Loss for 100ft at 450 MHz is about 2-2.5 dB, very Low-value for a cheap cable. For transmittion is a cheap choice, if you have up to 5-10 Watts maximum Power on UHF.
Hope that helps
73, Mak SV1BSX
--- Mike Miller mmiller@nctc.com wrote:
Anyone have any experience using 75 ohm CATV cable on 70 cm?
Mike KA5SMA _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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I read about it and I have dude what kind of 75 ohms cable are you using ... In 70 cm I am using CATV hard line 1/2 inches for about 50 feets and in the rotor section I am using RG6, when AO40 was ON I can run 100w and no problem about the RG6 cable :-) In other way I am using same cables for EME in 144 MhZ and I run 400w with any problem that you are describing, I know that CATV hard line may be is not a problem but RG6 have no problem also, here SWR both instalations are 1.1 :-) I recomend 100 % both cables Sincerely Al XE2AT
From: SV1BSX sv1bsx@yahoo.gr To: amsat-bb@amsat.org Subject: [amsat-bb] Re: 75 ohm CATV Cable on 70 cm Date: Tue, 22 May 2007 02:19:41 -0700 (PDT)
...yes, I tryed that on my 2nd QTH because my experience with 100ft of RG213 was very bad on UHF.
It was Sunday - no chance to buy something better.. so I decided to replace the RG213 with 75 Ohm TV cable.
Well, the receiving-difference it was spectacular! With 75Ohm cable it was possible to hear Loud & clear the FO-29 downlink, with RG-213 not good enough! The same I noticed with other Satellites and weak signal ground stations.
Later, after few weeks I replaced the 75 Ohm cable with AirCom+. Nothing changed between 75 Ohm TV and AirCom+ in the receiving! Absolutely equal receiving between the two cables, even if the AirCom+ was "10 times" much more expensive cable!
But in transmittion, it's obvious that the 75 Ohm cable has problem. It is not the mismatch (SWR 1.5) but this cable probably can not drive output Power bigger than 5-10 Watts. I confirmed that with 2-3 RIGs and several type of antennas. If you have output Power bigger than 10 Watts, is possible the RIG to decrease the Power output (ALC action? protection? I don't know!)a few seconds after PTT's press. (I'm talking always for UHF band).
So, from my experience I believe that the 75 Ohm is excellent in case you need a separate cable from UHF-LNA output upto the Shack. I noticed that the Loss for 100ft at 450 MHz is about 2-2.5 dB, very Low-value for a cheap cable. For transmittion is a cheap choice, if you have up to 5-10 Watts maximum Power on UHF.
Hope that helps
73, Mak SV1BSX
--- Mike Miller mmiller@nctc.com wrote:
Anyone have any experience using 75 ohm CATV cable on 70 cm?
Mike KA5SMA _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
____________________________________________________________________________________You snooze, you lose. Get messages ASAP with AutoCheck in the all-new Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/newmail_html.html _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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participants (5)
-
Alvaro de Leon Romo -
i8cvs -
kc6uqh -
Mike Miller -
SV1BSX