75 ohm coax
Locked
 
|
If you have 75 ohm coax, I would just try it. If the Z of the antenna is in fact around 35 ohms, the Z at the shack end may be close to 35 ohms on some bands, but on others the Z will be transposed to well over 100 ohms with an SWR probably over 3 to one. One of my dipoles has a SWR at the top of 75 meters of approximately 4:1, and I occasionally venture up there, but my K3S with internal tuner does not complain and quickly matches it to about 1:1. Not ideal and this is not the way I usually build my antennas, but the loss is not too bad. If you can build a unun with approximately a 1:2 ratio this should solve your problem. If it does not cover all the way from 80 to 10 with low loss, I would not worry too much about say 10 and 12 meters now, since some loss, and/or lower power output should not be a problem with our sunspot situation. If you happen to have lots of 75 ohm cable, you could parallel two runs of exactly the same length, the pair would have a Z of 37.5 ohms,
so nearly perfect if your actual antenna Z is in the vicinity of say 25 to 45 ohms. Not suggesting you spend much money on the coax, but if it is cheap or free, you could do this. Later if you change antennas you would have an extra coax run already in place. The power handling of the dual coax runs would be at least the same as a single run, and the loss could be either slightly higher or lower with the dual run depending upon whether the loss is I squared R, or due to the dielectric characteristics, but I would be surprised if the loss differed much at the HF frequencies. Just another idea to think about, not necessarily a recommendation. Rick KL7CW Sent from Mail for Windows 10 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
This all reminds me of the difference between when I was a young teen getting started as a ham vs now.
As a kid I would put things together or throw em up. Only worried about it after it didn’t work. Nowadays, I plan & overthink things to death before getting anything accomplished. I prefer the old way. 73, Josh W6XU Sent from my mobile device > On Apr 1, 2020, at 4:20 PM, Frederick Dwight <[hidden email]> wrote: > > If you have 75 ohm coax, I would just try it. If the Z of the antenna is in fact around 35 ohms, the Z at the shack end may be close to 35 ohms on some bands, but on others the Z will be transposed to well over 100 ohms with an SWR probably over 3 to one. One of my dipoles has a SWR at the top of 75 meters of approximately 4:1, and I occasionally venture up there, but my K3S with internal tuner does not complain and quickly matches it to about 1:1. Not ideal and this is not the way I usually build my antennas, but the loss is not too bad. If you can build a unun with approximately a 1:2 ratio this should solve your problem. If it does not cover all the way from 80 to 10 with low loss, I would not worry too ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
In old days hams fed 10:1 antennas with ladder line and did well.
Just keep feedline loss to a minimum. I feed my apex high delta loops direct with a good toroid coax choke at feedpoint at bottom corner (low impedance) near the shack. Coax is short and lmr240, works great. I tested 2:1 & 4:1 baluns etc on previous advice and the result was not as good as a good direct feed with high impedance choke. Look out for vk4tux on FT8. On 2/4/20 9:32 am, Josh Fiden wrote: > This all reminds me of the difference between when I was a young teen getting started as a ham vs now. > > As a kid I would put things together or throw em up. Only worried about it after it didn’t work. Nowadays, I plan & overthink things to death before getting anything accomplished. I prefer the old way. > > 73, > Josh W6XU > > Sent from my mobile device > >> On Apr 1, 2020, at 4:20 PM, Frederick Dwight <[hidden email]> wrote: >> >> If you have 75 ohm coax, I would just try it. If the Z of the antenna is in fact around 35 ohms, the Z at the shack end may be close to 35 ohms on some bands, but on others the Z will be transposed to well over 100 ohms with an SWR probably over 3 to one. One of my dipoles has a SWR at the top of 75 meters of approximately 4:1, and I occasionally venture up there, but my K3S with internal tuner does not complain and quickly matches it to about 1:1. Not ideal and this is not the way I usually build my antennas, but the loss is not too bad. If you can build a unun with approximately a 1:2 ratio this should solve your problem. If it does not cover all the way from 80 to 10 with low loss, I would not worry too > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
The plus of RG6 is low price, less than 10c a foot. In receive applications,
they seem to be lasting forever. In transmit too but small nuisances are necessity to use a tuner for low SWR antennas and nonstandard connectors. But running two in parallel does not make any sense. Half a year ago I found Rg6's 50 Ohm equivalent on ebay. Altelix AX240 for $99/1000ft. Measured parameters same as LMR240. The plus of cheap and good 1000-ft roll (with crimp connectors that can be attached in 30 sec) is that the coax can be cut as needed, with no worries about cost. Ignacy NO9E -- Sent from: http://elecraft.365791.n2.nabble.com/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
The same PL-259 reducers for RG-8X works for RG-6. Same for BNC connectors.
Bob, K4TAX Sent from my iPhone > On Apr 2, 2020, at 10:13 PM, Ignacy <[hidden email]> wrote: > > The plus of RG6 is low price, less than 10c a foot. In receive applications, > they seem to be lasting forever. In transmit too but small nuisances are > necessity to use a tuner for low SWR antennas and nonstandard connectors. > But running two in parallel does not make any sense. > > Half a year ago I found Rg6's 50 Ohm equivalent on ebay. Altelix AX240 for > $99/1000ft. Measured parameters same as LMR240. The plus of cheap and good > 1000-ft roll (with crimp connectors that can be attached in 30 sec) is that > the coax can be cut as needed, with no worries about cost. > > Ignacy NO9E > > > > -- > Sent from: http://elecraft.365791.n2.nabble.com/ > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
In reply to this post by Ignacy
On 4/2/2020 7:58 PM, Ignacy wrote:
> In transmit too but small nuisances are > necessity to use a tuner for low SWR antennas and nonstandard connectors. It depends what you regard as "standard". The TV/CATV "standard" are F-connectors, available almost everywhere the cable is retailed. There are 75-ohm BNC connectors available. When I ran a TV signal measurements unit decades ago, we had lots of 75-ohm cables with BNCs on them and we painted a red ring around the connector body to distinguish them from 50-ohm BNCs. "I love working with standards because there are so many to choose from" > But running two in parallel does not make any sense. Yes it foes if you want a shielded balanced line. Just disregard the losses and impedance mismatches. 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 From a Clearing in the Silicon Forest Beaverton (Washington County) Oregon ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
In reply to this post by Bob McGraw - K4TAX
On 4/2/2020 8:37 PM, Bob McGraw K4TAX wrote:
> The same PL-259 reducers for RG-8X works for RG-6. Same for BNC connectors. The center conductor "pins" for 75-ohm BNCs are of a different size as compared to 50-ohm BNCs,. 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 From a Clearing in the Silicon Forest Beaverton (Washington County) Oregon ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |