The PL-259 and SO-239 start showing loss at 2M and are quite poor at 222 mHz when tenths of a dB matter. Yes, they are reasonable at 432 for some reason. Ive run a Mil Spec pair to the uncomfortable to touch point with 1500W on 2M MS skeds using the 3CX1000A7 amp I built over 30 years ago. The N replacements were barely above room temperature. Several well respected hams have claimed they are poor on 222 but I went directly to N with the 8877 amp and 400W is my limit on 432 with the AM-6155 and its N's. Ive used the CATV equivalents since about 1979. The loss is lower comparing equal sizes and the price was right. Carl
There is coax, then there is COAX and then there is COAX!! There are all qualities of coax and there are various qualities of coax connectors. Some are good, some are ugly and some are just plane BAD. I read an article years ago that the PL-259 / SO-239 combination was never designed to be 50 ohm connectors. They were designed to be somewhere around 62 ohms which was a compromise between 50 ohm and 75 ohm coax. For most applications back then it didn't really make much difference and the frequency of operation was below 300 MHz. The same can be said for a lot of ham operations today at HF and lower VHF. Additionally they were not designed to be water proof by themselves. Since that time various 'smart' people have made modifications to the original design to try and overcome some of the original 'flaws'. From practical experience, I can tell you that two things can turn a piece of coax into a dummy load in a hurry. They are heat/sun and water penetration. I can't tell you which brands are better or worse but a lot of RG8X sold at hamfests is not worth the money you pay for it. If exposed to strong sun light or heat (like installed in an attic) after 6 months to a year it turns into a good RF attenuator. The chemicals of the outer jacket migrate /leach though the porous shield into the foam center insulation. When that happens, the losses in the coax go way up! There are brands where they use a different outer jacket material to prevent that from happening. In any case, buyer beware! Even RG-8 size cables can suffer from a similar problem if the outer jacket material, shield and center insulator material just happen to be the wrong combination. Water penetration is a BIGGIE! I saw a 50 ft piece of LMR-400 turned into a big attenuator in about a month because the connector at the antenna end was not installed correctly and water got into it! It turned the 20 watt output of a 450 MHz LMR radio into just barely enough power to move the meter on the 5 watt scale of my watt meter!! And, you haven't lived until you take the coax connector off the back of a 450 MHz. repeater and water runs out of it! The coax, by the way, was 1/2 inch aluminum hard line!! The repeater end of the coax ran inside the building for at least several feet so the water hadn't gotten in at that end! The antenna was a 100 ft or so up a grain storage silo. So either the connection at the antenna wasn't water tight or the aluminum outer shield had gotten damaged and penetrated some how. I have also seen water wick itself up the shield of a piece of coax and then, after reaching the highest spot, siphon itself down the rest of an 8 ft piece of coax. (Think a piece of solder wick!) So, my recommendations: 1. Use the best quality coax you can afford. 2. Use as few good connectors or slices as you possibly can. 3. Make sure they are installed correctly. 4. And then, water proof them like your life depended on them being water proof! Dave K3GAU
Uh oh.... You generate an impedance discontinuity when you do that, and the coax starts to radiate....
I understand this line of thinking but why would a barrel connector be any better? It looks like if you are careful on how you configure the braided part of the coax on the soldered connection, the impedance difference would not be much different than a fancy connector. Maybe it does? not a rf engineer...
If you really went nuts trying to make a proper concentric splice that didn't appear to be a major impedance bump then sure you you might be able to sneak by not using proper connectors. What might work adequately at say 1.8 Mhz might be really crappy at 30 MHz or higher. The magic numerical term is Return Loss and that varies with frequency.
When I worked in a calibration lab at Fort Hood, TX many cables had to be handy for interconnections. To save some time and reduce the number of cables, I cut the locking ring from a BNC connector and plugged it directly into the Type-N socket found on a lot of military equipment. The pin is a slight mismatch but it's good for plug-n-chug as done when putting a cable between a test set and the unit under test/calibration. What does this mean? It means that the BNC connector is just as good as a Type-N connector when you keep in mind the types of cable used with the respective connector. For example, using a BNC connector with the appropriate coax when lashing the rig with the amp, tuner, etc., is great, especially considering the inherent flexibility of RG-58 or similar compared to the flexibility of RG-8 sized cables. Of course, though, larger cables are better for runs to the antenna for their durability and overall power-handling characteristics. But a short piece of smaller cable with BNC connectors may well be a better choice when lashing equipment together. The problem is, of course, that most equipment is designed to use the PL-259/SO-239 connectors as the connector type of choice and to change connectors or to use adapters seems, for the most part, like going the "long way round" as they might say across the pond. More fodder for the frontal lobe...
With proper thought and making sure the two cables did not see a "lump" in the finished cable, impedance-wise. I think it would work, especially at lower frequencies. But, nothing is as simple as it seems. —Murphy At a field day event one time, I discovered the 2M antenna connector on the rig end of my mag mount coax had a faulty connection. It was not repairable (crimped) and we needed the 2M rig for talking in some people who didn't have map-reading down as an art. However, I had a short cable with the PL-259 on it so I cut off the connector with about a six-inch pigtail and spliced them together by folding back the shield, soldering the center conductors and taping well with electricians' tape to keep the inner diameter close and keep down any shorting to the shield. Then I folded the shield back over the coax and taped it up good and tight and putting the 2M rig on the air... Note that the 2M antenna coax was RG-58 style on the magnet mount and the short pigtail used RG-8 coax...! The hack job is still working on my 2M mobile antenna. Also note that I highly recommend NOT doing this unless it's some kind of emergency. Being so lazy, though, I have not changed the connector, since I rarely use 2M mobile, but is still works! By the way, that "fix" was used on field day by mounting the antenna on the steel roof of a nearby lean-to. Almost anything can be done in an emergency.
The "UHF" connector was designed in the 1930s. Back then, 30MHz was considered UHF. The UHF connector was derived from the banana plug, the center pins are the same diameter. The characteristic impedance is between 30 and 40 ohms. Only CB and Ham equipment use UHF connectors.
On lower frequencies, the additional loss would not be noticeable. The major issue is to stress-relieve and weatherproof the joint. Even on UHF (432 MHz) it can be done without seriously impairing the electrical properties. As an impoverished grammar-school student in 1972 I made up a phasing harness for 4 432 MHz Yagis using pieces of RG-213 which were soldered together at the joints. By carefully joining the inner conductors, replacing the insulation material around the conductors and finally equally soldering together the shield braids, a three-way joint that worked OK was created. It took a lot of electrical tape and vulcanising rubber tape to make the joint sufficiently rugged and weatherproof however. I brought this antenna with me to University, and later got the opportunity to compare the soldered joints to type N Tee-connectors and UG-21/U plugs using both a network analyser and a TDR. There were no substantial differences in performance between them, insertion loss and return loss were in the same order, but there was a small impedance "bump" visible on the TDR. 73/ Karl-Arne SM0AOM
You did what hams do: Make do with available material/s and put it together with a lot of thought. Most of us try to do this when we lay out and build up a chassis with some "exotic" circuit but antennas/coaxes are not an exception to the rule. Knowing how others did it and to what success is interesting. What is learned from these explanations can be useful in future building plans.
Ive heard of some industrial gear use them and RG-8/213 as high as 10kV. Ive used real Teflon versions to ~5kV several times rather than old school Millen connectors which are "rated" to 7kV. Those are quite hygroscopic and fail even at 2kV. VHF 2 way radio gear used them by the thousands at VHF for decades, as well as some ISM gear at 13.56 MHz and in the 40 MHz range. Carl
The connector we refer to as a PL259 / so239 combination are stolen from.the marine world. Originally used as DC connectors. --Shane KD6VXI
