Can you Connect Different Types of Coax? (
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- เผยแพร่เมื่อ 8 ก.พ. 2025
- Troy Lerner, KF0AFQ, has some heliax, RG-8X, and LMR400 and wants to know if he can connect them to make one long coax. Watch to learn more.
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Well thanks so much for answering my question, Dave! That was exactly the information I wanted to understand. Just so you know how I got myself into this pickle-- I bought a lot with hundreds of feet of various coax pieces for $10 at a garage sale. I own a good crimper with a large set of dies. I've purchased connectors for the "normal" coax, and learned how to reuse the Heliax N Connectors. So, why would I mix and match to make long runs? Because I can! (and I just hate waste in the world, so this makes me feel good too). Thanks, Dave!
I would use the Heliax for a mag loop antenna or 3 :-)
Since this is garage sale coax, I think that you should check the cable for loss before you use it. Old cable that has been laying around for years may not be that much of a bargain.
@@terry5089 you’re right. It was pulled from indoor conduit. Jacket in great condition. Checks out on the VNA, and the measured loss is very close to the manufacturer’s spec sheet. I think I got a steal. ….the 20 Heliax N connectors are worth it alone (they go for $10/ea used)
I have used Heliax before for commerical use and one thing to consider it that it is open inside and can get moisture in it and mess with the ballance and or short out. This is why the center is usually pressurised with dry nitrogen gas and monitored for mositure. This is one of the reasons it ususally only used for high power or microwave stations. If you can't keep it charged with nitrogen then mount it between vertrical and around 40 degrees and drill small holes at the lowest point to allow the moisture out. Trying to seal it will only keep the moisture in and it will build up to a lot of water inside.
@@TroyCraft Excellent! You did get a steal. Congratulations.
I have a tower with 3 hf antennas and 2 vhf antennas. The tower is 160 feet from my ham shack. Through an underground conduit, I have two heliax cables, one for hf, one for vhf. At the tower end, each heliax goes to an adapter to coax, then to a remote antenna switch, with coax to each antenna.
I used heliax for the 160 foot run to minimize loss over that distance. Inside a conduit, the heliax does not flex or move. On the ham shack end, I also use coax and antenna switches to allow my multiple rigs access to the antennas
73 Ray K1XV
Sounds like an amazing setup. Thanks for sharing!
That's what I did with my tower too. The tower 75 feet from my house and 80 feet tall. So, 155' to the antennas. I used three runs of 7/8 Hardline to the top of the tower, then transition to RG-213 to the antennas.
As a former broadcast engineer, there are adapters from heliax to whatever connector you need. But, heliax is way overkill for most ham installations and is very difficult to work with compared to RG8x or RG213..... k6sdw
In fact at broadcast stations it is generally the practice to use short flexible jumpers at he ends of heliax runs. At one studio I installed a 100 foot feed line of 7/8 inch heliax for a 946.0 MHz system with RG213 jumpers at the transmitter (Moseley PCL606C) and the antenna (Scala PR450U). The heliax was terminated with N females and the 2 foot jumpers were N male to male. You can get heliax connectors from Andrew Corporation.
For the guy who asked, you build resistance or connection issues with additional connectors. You want a solid, uninterrupted line. The connections can get wet or dirt. Oxidized or rusted or what have you. If you need 100’, but a 200’ reel. I use rg8x. I only needed 25’ of the 500’ reel. I paid less than $120 on Amazon. I have so much, I wanna hide the reel. But I made more custom cables that were cheaper than buying pre-made. As an added point, I could have made and sold several lengths at a ham fest! Plus, it’s fun making things!
Very useful discussion of the different types of coax. I need to check out your other videos on LMR connectors.
Times Microwave also makes an "Ultra-Flex" version of their LMR400 cable called LMR400UF. It is not as stiff as the LMR400. I have installed crimp-type PL259 connectors on LMR400UF with no real difficulty or special tooling other than a compatible crimp tool for the shield (the center pin gets soldered). The PL259 connectors & crimp tools were all purchased from eBay and worked great and weren't ridiculously expensive. 73 Dave.
You could just use "N" connectors for all cables. (Actually they do make pl259 connectors for heliax.)
My concern would be the different velocity factors involved.
LMR-400 is a very stiff cable however LMR-400 ultraflex is not. The FAA uses miles of this ultraflex cable.
Dave, I looked it up . Walmart has Andrew Heliax. Connectors also.
I'm surprised you don't have a board with coax samples for show n tell. Or a link to a good picture of one.
Installation crews often have short spool ends that are going to be scrapped, so for cash money if they've got 25' left on a spool, they'll gladly sell it if you ask nicely.
Just saw you on page 50 of the July 2021 QST magazine. Congratulations!
With regard to the gentleman with the Heliax, RG8x, LMR400 coax , I'd suggest he buy a 100 foot length of either the Rg8x or LMR400 and not buy multiple connectors which add expense and the addition need for multiple connection's waterproofing, and potential future problems...
Plus the extra cable length could provide an RF current choke.
Hello Dave: As is mentioned by other followers here T M has the LMR 400UF or Ultra Flex which is a lot easier to work with and is sold by DX engineering along with their new design of crimp type coax connector's, B T W I saw and read your new column in QST magazine and found it interesting !!! I Also was an I.B.M. Employee here on the east coast at the East Fishkill plant
in Dutchess county, state of New York, I worked there for 31 years !! The EF plant had about 13 to 15 thousand people there during the 1980's into the 1990's John Bellas 73's from KC2UVN
RF parts has heliax connectors of all kinds. I have the 1 inch and 1/2 inch Andrews that was a gift too me with and installed the PL -259.
I mix n match coax at my station. Outdoor HF runs are LMR-240. Short patch cables inside are RG-58 or LMR-240 ultraflex because they are easy to bend and work with. 73 de WB4DW
I dont remember if you mentioned this, but is there a certain order you would want to put them in? (Ie. Lowest loss closest to the transmitter)
v
Velocity factor is different between the different cables..
I run 50 feet of LMR 600. Stubborn and mean to work with, but tough and low loss for VHF and UHF. Maybe overkill, but viscously cutting down every potential loss does yield results.
Now, Mr. Casler, how does different velocity factors affect potential SWR and data when you put two different coax in line?
Dave is correct with the point of soldering LMR. you can't really solder aluminum and the high heat trying degrades the dielectric. Crimping is the only way to go. I use RFC connectors.
Dave
I use the DX Engineering version DXE 400 MAX with Chinese clamp type PL259 which are assembled similar to N connectors. You need a soldering iron for the center conductor and thin wrenches to tighten the connector, no apecial tooling required.
The helix with a coiled insulator allows pressurized dry air or nitrogen to permeate the entire feedline and the antenna itself in the case of high-power broadcasting. Special fittings are used with gas ports to connect the dry, inert gas supply such as is provided by a dehydrator. These connectors are very pricey. Such heliax cables are usually large such as 1-5/8" or larger. 1/2" and 7/8" heliax is usually foam filled and not pressurized. Connectors for 1/2" heliax are available from Commscope sold under the brand name "Positive Stop". Not too difficult to install. 1/2" N about $25 +/-
Hmmm I've used Heliax on VHF / UHF since the 1980's
As you stroll along the riverbed of RF with Dave, you stop and pick up the gems amid the rubble.
Thanks maaaaan!
Hey Dave I'm trying to find an episode where you talked about tubes creating distortion/harmonics. Maybe you can re-visit this topic. Something explaining why old tube radios sound "warm" and distinct on the air.. thank you.
I worked on Motorola 2ways and all the Hardline I worked with had female type N because they used short jumpers of RG213 or RG214 Hardline to the antenna at the top of the tower and to the radio at the bottom. It is not easy to bend Hardline! Most of the time I used pipe benders! One wrong bend that kinks it and it is trash! And it is very hard to bend but easy to kink! I wished I had some! Great for long runs up the tower. Some of the connectors have a place to ground the outside of the cable! If you think the cable is high priced, the connectors are Brass and some of the bigger ones I have seen are over 2 lbs!
Just wanted to add this. I’m using LDF4-50A currently and have some 7/8 which I’ll be adding between the shack and the tower and then will add the LDF4-50A at the end to make the shorter bends. I’m not using this because I have to, but because I was able to work out a deal, plus its with less than 1db attenuation up to 200MHz, and 70cm is around 1.4db att at 100 feet, high quality and most of the RF project where in the GHz range before getting the HF rig. Anyways, I had many N style connectors, for the LDF 450 and 7/8 so rather than attempting to re-terminate to PL259, I kept the N style and purchased adapters from DX Engineering which were N Female to PL259 and it seems to work great. Messi and Paoloni makes some compression style .50 PL259s, however they are designed for stranded shielding and I’ve not got them to work with the LDF4-50A as its a style of Helix with good flexibility.
DXE’s N to UHF adapters are silver plated brass and great quality. I’ve had issues with the Amazon adapters, so I changed all of them out with the ones from DXE which currently cost $16.99 for 2x. They are made by NTE Electronics part number DXE-06-0102-2, and they can be purchased elsewhere but they seems to be higher.
My 2 cents, N style compression connectors are available for Heliax. UHF/PL259 connectors I had trouble finding, plus the N style connectors are great, so just adapt them over to UHF.
The N compression connector spec sheet should have the dimensions needed for installation. Heliax can be a pain unless you have the right tools, so plan on using a tubing cutter for the jacket, razor knife for the dielectric, and a file to taper the center conductor normally needed for compression style connectors. You can also buy some slick prep tool that mounts to a drill, which speeds up the process quite a bit, which takes about 10 - 15 seconds. Although I had to trim it afterwards for the connectors I had, it performs all of the operations needed in the spec sheet, assuming you use a compatible brand connector. They cost around $150 for .50 Heliax, and I would not buy one if I only had a couple to do. Commscope makes some, CPT-F4B for .50 Heliax, but hold you wallet for 7/8, as they are significantly higher, which is why I’m not buying one. If I did installs for a living, yes they save a tremendous amount of time, but for a couple here and there, no for me. Manual prep tools are also available at around $40.
Side note, I use Amazon connectors still, but not for anything with some power.
Hope that helps a little
With regards to LMR-400, why do you recommend crimp over solder? I thought soldering was supposed to be better for longevity and connection strength? I’m a new HAM so I don’t really know what’s best!
I have used solder connections on LMR 400. There is a sticky goo in the coax that is miserable to work with so I prefer crimp connectors for LMR.
Times Microwave recommends crimped connectors. Get their brand connectors and toolset. Watch their "how to" videos on YT. Back in the 1980s when I first got into amateur radio most crimp connectors were garbage. Things are different in 2021.
I have seen many different coax cables, all labeled as RG-8X. Many of these have SIGNIFICANTLY different RF characteristics, including their loss figures
.
Which brand of RG-8X do you use Dave ?
Yea, you have to be careful with the RG-8X, as quality can vary wildly. That's why I just use Times Microwave LMR-240 instead. It's roughly the same size and quality is assured. They make a "regular" version, which is pretty stiff, a direct bury version which is stiff but has some goo in it to protect against water invasion, and an "ultraflex" version which is easier to bend (but still not as easy to bend as, say, RG-58). Anyway, if it says Times Microwave on the jacket, you know it's good quality.
Some of the large Heliax LDF (low density foam) the connectors will run more than 150' of LMR400. I know, everything in my shack over 30mhz is hardline. But I have a source for pull out hardline.
What about velocity factor?
I have a Viking messenger that has a “ plug in” type connector.
What is this connector called and where can I get them?
Each cable has a different velocity factor due to the differing dielectrics. I’ve not seen a discussion of that mismatch’s effect, if any, on reflectivity or loss. Some have proven through experiment that the loss in connectors and adaptors is wholly insignificant at HF. The biggest real-world concern is keeping water out of the couplings. Water always wins.
I chose LMR-400 (actually the Andrew/Commscope CNT-400 equivalent because I got a spool at a great price) for its lower loss at 6 meters. It’s essentially invisible up to 30 MHz. Antenna, and especially feedline, efficiency is not the place to skimp. That’s like hooking up a garden hose to a fire truck...lots of power pinched off at the outlet.
I use ordinary crimp PL-259’s (properly sized) on the CNT-400. It’s double shielded, tinned braid and foil, so you could solder, but not many people get that right under any circumstance, and it’s tricky with 400 because of the foam dielectric. You can’t be a soldering hack. Melting the foam changes the impedance, or if egregious, can short the cable. A properly prepared crimp made with the correct die in a good tool makes a very good connection. The center conductor is copper clad aluminum. It solders easily. Get the iron hot, get in and get out quickly before the heat can conduct up the wire and melt the foam.
I use LMR-240 ultraflex upstream of the amplifiers. The 400 is too stiff to be straining on all the antenna connectors and switches. The 240’s loss is insignificantly higher in short runs around the radio room and its power capacity is more than adequate ahead of the linears. It’s so flexible it’s almost limp.
Several of the coax manufacturers have charts online, comparing loss and all the other interesting characteristics of the various solid and foam dielectric cables. Dealers have these too, but they’re sometimes rather simplified.
I have two 75’ runs for vhf/uhf. Would RG-218 be sufficient or would it be better to have lmr-400?
Have a look at the losses per foot / metre graphs. 3 dog Biscuits is half power. 6 dog Biscuits is an S point.
Big differences between 70cm and 7MHz
If I was doing weak signal VHF/UHF work, I would get the LMR-400.
Besides the impedance bump every time connectors are inserted in the line, there's another place where water can migrate in.
Now I know, thanks
Most thinner heliax uses N type connectors anyway...
Thicker stuff uses mainly seems to use 7-16 DIN connectors
Adapters between the 2 are readily available (used extensively in cellphone infrastructure) but they aren't particularly cheap
DE 2E0LNE
He did not mention the size of the heliax, sizes range from quarter inch to nine inches!
Ok. You said something that I couldn't make out. You said that instead of using the barrel connector, use something else and you won't have the barrel connector reflect. What was the something else that you said to use
My apologies for resurrecting an older video, but I have a relevant question concerning splicing of different coax cables, all 50 Ohm:
I was just gifted around 200 or so feet of FXL-540 Commscope (1/2 in hardline with foam dielectric) and not only has it been discontinued for over a decade, connectors seem to be hard to come by and take special (i.e. expensive) tools to terminate properly. That being said, is it possible for a non-connector based (solder) splicing of two types of coax without major technical issues? Say, a 6' RG8X pigtail spliced to each end of a 150 ft length of hardline?
I'm not running any major power, 100 watts or less and also no long lengths either, around 150 ft total.
What say you?
73
No mention of V.F. ?
Dave, here is a challange for you. try to test to see the loss caused by connectors in a coax line, even if you add 10 or more in line you probibly not be able to measure it at HF frequencys. It is an old story with no basis that pl259 connectores cause a 1db loss, it is not even 0.1db (if they did cause this much loss they would be hot in your hand when you tansmit) take care and as always thank you for your great videos.
I was once in a rush make some RF measurements at 2.4 GHz. The only adapters I had that day were my PL259 versions. The results were absolutely horrible,
The next day I found my BNC adaptors, and everything worked fine with them.
@@howardhiggins9641 well if you look at my comment you will see that I said HF not UHF. PL259 is is best used for MF, HF and and some VHF. The marine industry uses it for all their VHF radios with no problems, other than poor solder jobs.
If you connect two different coaxial cables together, even if the characteristic impedance is the the same on both cables, there will be the equivalent of a capacitance put in parallel to the line. This effect has been calculated in 1944. See the paper by: Whinnery, Jamieson and Robbins. This capacitance may eventually cause a reflection or phase shift. This effect can be minimized in theory by using a taper interface between the two cables. This is only theory because I have calculated the value of the capacitance and found that for ham radio frequencies the effect is totally negligible.
Also, RG-58 RG-59 and all those designations were old military specifications that have long been abandoned. Nowadays, the only expectation when you buy cable from the cheap suppliers is that somehow the current flows thru it! Even that is not guaranteed. For example you discover that solid copper center turns out being plated aluminum or mechanical tolerances are not respected. Not to mention the quality of dielectric or the shield. It is a disaster when you have to patch a cable with electric tape when installing high quality high price connectors.
On the other hand, it you insist for having properly specified cables and connectors then you will have a big surprise because those are government suppliers... Good stuff is rare and expensive.
RG213 is military spec. One might expect the shielding to be adequate for most ham use.
You can buy a lot of LMR for the cost of Andrew heliax connectors.
If one band takes priority, you can place your connector/adapters so they fall on the odd quarter-wave lengths of that frequency, when taking into account for the propagation factors for each cable , so the introduced impedance bumps 'disappear'. Oh yea, you'll go broke terminating the Heliax.
i am only 28 seconds in, and i never subscribe - but someone that takes random people's questions and then (i presume you'll:) answer then/solve their issue is the type of stuff that people SHOULD get wealthy from youtube for their content
In fact if you could have an infinite length of 50 ohm coax it would measure 50 ohms on a DC multi-meter. Alternately a discharged finite length of 50 ohm coax would measure 50 ohms at the instant of connection. Think looking a an electrolytic capacitor using an ohmmeter. This is why it is sometimes called the surge impedance. If you cut an infinite coax and replace the remaining infinite length with a resistor equal to the characteristic impedance it will measure the same as the infinite length.
I don't see any technical problem here as far as the velocity factors. It's not going to make any difference. Besides, how are you expected to feed an antenna on a rotator with half inch Heliax?
Oh, I don't know about WalMart. I use Heliax for my Uhf vert gpa and Yagi directional for the repeaters. The 1/2" Heliax is just on the tower about 50 ft. I use1/4" superflex for the gpa tail and the yagi tail The main feed coming out of the shack is 3/8 superflex comming from the switch to the polyphaser about a 15 ft run. This particular station has nothing to do with amateur radio though its for coms on a farm and farm to farm and field use for coordinating planting crews and field work and security. I get this from the Antenna Farm if that matters. It's a charity thing . Using this stuff for anything less than vhf is pointless and a waste of money. I would suggest if possible for him to use just one type of feedline at a single length to avoid issues.
Would heating be an indication of Impedance mismatch?
he showed there was no impedance mis-match
@@davep6977 IF there was a mismatch, would heating show where it was? That was my question. 73
As a retired Broadcast Engineer and 2-way shop Manager, smaller Heliax, such as 1/2 inch, is perfect for 2M and up. It is not too difficult to work with. It is not too hard to find used in good condition. 7/8 inch Heliax does get much harder to work with. When you get up to 3 inch Heliax and up it is way overkill for Amateur purposes. Mostly, Amateurs should stay away from air dielectric Heliax. Air dielectric is lower loss, but keeping it dry is difficult. Connectors should not be reused. New connectors are very expensive, being mostly machined brass. w0fen Robin
I have 260 feet of 1/2 inch Heliax with N connectors on each end in my shed. Salvage from a commercial radio system that was dismantled. Got it for free. The stuff is really stiff.
it's all relative. I have 2 runs of 7/8 hardline. But believe it or not, I'd rather put on 7/8 connectors than 1/2"
By the time he got done getting all the right connectors, ends, tools required to get it to work, might just be better off using that money to buy a single 75' or 100' length of continuous RH8x or other decent cable. Not to mention the losses with each fitting and potential or water intrusion in each one.
LMR-400 UltraFlex is NOT stiff like the standard 400.
flex is stranded center conductor as opposed to solid
@@davep6977 yep, that’s why it not stiff.
I would sell the Heliax and use that money to buy about 500 ft of LMR400...
Thank you, Dave.
Someone has already answered the Wal-Mart question.
Have a great week. N0QFT
"Walmart" lists all kinds of strange and exotic stuff you CAN'T actually get there. They are attempting to compete with Amazon (third party vendors) and doing a miserable job of it...
Dave, use examples/samples instead of drawing.