Well, some recent CB shop horse shit jockey experience to share. I wanted to try a dual antenna setup. Not cophase, but on a antenna switch, to try different antenna with this skip. One top load, one center load. Just an experiment for shits and giggles. I found a shop that sold one of the antennas I wanted, a Skip Shooter, and a antenna switch. That guy tells me he's got 35 years experience, and knows his shit. I asked about cophased antennas, and he said they transmit the signal left and right, and the coax needs to be 75 ohm, and must be 18', whether single or cophased, 18' each leg. OK, I've heard and read the ohm info before. So, I ask him to make me up me up some coax, RG 58UA. He solders the amphenol connections, I pay, and off I go. I try to hook up the coax, and it won't fit. Clumps of solder, and looked to be over heated. I scrape down the mess to fit. Swrs really high. I notice the connection is a bit loose. I hold it tight, tape it up, swrs go down, but are still high. Bad solder job from "the expert," and I noticed it was 8x coax, not RG58au as I requested. Yes, I should have checked before leaving, buyer beware, etc, but for "trust!" So, I tried some cheap truckstop coax, RG58AU, Swrs come down again, but still high. Can't tune the 5 ft SKip Shooter low enough. I tried the switch. Swrs double, both with a 3' jumper, and the 10" or 12" lead on the back of my radio. Bad switch, or just bad idea. I stop at another cb shop. He tells me he's a ham operator, a licensed tech, with 29 years experience. I ask him about coax, single and cophase. He says all coax, single or cophase should be 50ohm. That a single coax should be 18', but cophased 9' each leg, 18' total, no harness, not 75 ohm, but 50 ohm, and both 9' legs go into a T connection, and into radio. Now, Ive tead from actual antenna/coax material, that 50ohm cophased, especially into a T connection simply won't work. I asked him about this, and he got irritated, and claimed he's been making them up like that for years, and they work. He also said cophased antennas transmit signal front to back, not left and right. Also to ground more from antenna, directly to the frame. Now, I've heard from others, that grouding should be done in legs, sections. Say, from the antenna to the body, body to fire wall, fire wall to frame or engine. So, that's what I did. Yet another cb shop I went to uses lmr240 for both single, and cophased antenna setups, and said grounding the antenna system isn't a good idea, because the ground causes the truck to essentially become part of the antenna system. That "cb shop" also has one meter in the messy, disorganized shop. A small Dosy, period. But, he said he was a former electrician, so he segwayed after retirement into the cb tech trade. A struggling one from all appearances. He's also training his two daughters now to be "cb techs." No tech school, no knowledge of the various meters, and equipment, etc. I watched one of his daughters look up on YouTube how to tune a particular Stryker he was trying to work on for him. Finally, the CB tech who I go to for all my radios, as I by from no other, for 15 years now, due to all the aforementioned "experts," and "techs" out there, in these snip and clip, chop up cb shops, actually sold me my latest radio, a Ranger 69ffb4. Well, I don't know if it's his age, health issues, or what, but it hasn't been transmitting or receiving right, and I noticed it was throwing a 100 watt carrier on ssb, so I had one shop with actual equipment in view do a bench check. It definitely was throwing a carrier on ssb, and was not transmitting as it should, nor at the peak modulation, as advertised, both on both the box, or as told to me by the shop I purchased it from. 150 watts less on AM, and 75 watts less on ssb. An $850 purchase! The echo and talk back suck as well. Now I have to have a conversation with who I believe to be an honest tech, with actual knowledge and integrity. A bad radio, or a bad tune & alignment, or is he slipping? This was a first. All my other radios done, or bought there were top shelf! Anyway, just a long gripe about the various types of cb shop "techs" out here, most, not all Im sure, that are in my opinion, bullshit jockeys, snip and clip golden screw driver, smoke and mirror, and incompetent morons, that have no right behind a bench!
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Snip and clip, golden screw driver "techs!"
- Thread starter Slowpoke
- Start date
Well, had the discussion with the shop I bought the radio from. I was told to send it back to Ranger in California, not bring or ship it back to the shop, since its under warranty. Will the warranty be void, with any conversion, or mods done at shop? Not sure.
I would assume no warranty on a converted piece. MOST companies state this. As far as I know about cophasing, you use the 75ohm stuff so you get about 37 ohms to the radio, which is usually good enough to make it happy. You use a separate length of coax on each antenna to tune them individually before connecting the co-phase harness. Minor fine tuning may be required afterwards. And I believe the only time coax length matters is IF your antenna is using the coax shield for counterpoise. Ideally, the coax should be invisible to the radio. Someone correct me if I'm wrong, here!
That ranger with the carrier on SSB? My buddy just went through the same thing and smoked an amp. Sent the radio to
First Class Radio
3316 W. Chain Of Rocks Rd. Suite 2
Granite City, IL 62040
And the tech found a bad ground on the board that was seeking ground through the AM circuitry. They fixed it and works well.
The reason for the 75ohm and quarter wavelength is because when a 50ohm antenna is connected to a quarter wavelength of 75ohm coax, the mismatch is transformed by the coax to 100ohm at the other end. This is beneficial because when you tee them together in parallel, two 100ohm loads in parallel equals 50ohm (once again a match for the radio). If they went with 9', they didn't even take velocity factor into consideration.
The warranty work should be done by Chris Holland at Superior CB in Calif.
A carrier on SSB says the carrier balance might not be adjusted properly.
I dont think the conversion voids factory warranty, a phone call to Chris will answer that question.
His contact below in link.
www.superiorcb.com
Co phaseing two antennas requires 50 ohm coax to the " tee" or split, with 75 ohm coax in the actual harness.
See picture below.
From http://www.iw5edi.com/ham-radio/2464/antenna-performance-co-phasing
Now that is co phased, running 2 antennas at the same time.
To simply switch in between each antenna and run them separately would be 50 ohm coax.
You may find the the amp built into the radio has a spurious problem, if this is the case your beating your head against a wall trying to sort out swr problems with the antennas.
Putting the radio on a SA will reveal if that is what you are experiencing.
73
Jeff
A carrier on SSB says the carrier balance might not be adjusted properly.
I dont think the conversion voids factory warranty, a phone call to Chris will answer that question.
His contact below in link.
Superior CB Inc. | CB Radios Sales & Repair in Ontario, California
Superior CB Inc. is operated by Chris and Veronica Holland. As a boy, Chris started talking on the CB radio at age 11.
www.superiorcb.com
Co phaseing two antennas requires 50 ohm coax to the " tee" or split, with 75 ohm coax in the actual harness.
See picture below.
From http://www.iw5edi.com/ham-radio/2464/antenna-performance-co-phasing
Now that is co phased, running 2 antennas at the same time.
To simply switch in between each antenna and run them separately would be 50 ohm coax.
You may find the the amp built into the radio has a spurious problem, if this is the case your beating your head against a wall trying to sort out swr problems with the antennas.
Putting the radio on a SA will reveal if that is what you are experiencing.
73
Jeff
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Yes, I tried to explain the 75ohms to him vs 50ohms, but he got pissy, and went into his credentials speel. I'll contact that company. Thank you for the info!
So, a T connector is ok, as long as they're two 75ohn coax? Or would factory made 75ohm RG59au be better? I don't know why in his "29 year expert opinion," 18' max of 50ohm coax, split between two 9' sections to a T connector, to the radio, would be OK. There's just far too many "experts" out there, and so many splatter boxes to prove it!
Yes, as long as the coax between the tee and the antennas is 75Ω AND an odd multiple of electrical quarter wavelengths AND the feed points at each individual antenna is 50Ω, this will work. The length of the coax between the tee and radio can be any length of 50Ω. It does not have to be factory made to work well. However, 4 connectors and a tee will probably cost you the same as a pre-made 75Ω co-phased cable.
There is a lot of confusion out there about coax length, especially regarding people stating that adding 3 feet made a difference for them, so I'll very briefly cover the "what for and why" there because it is important to understand when this will work and when it will not.
If the load connected to the coax matches the characteristic impedance of the coax, the input impedance of the coax will be the same, 50Ω. However, if there is a mismatch between the coax and antenna, the coax will transform that impedance mismatch to something else at the coax input depending on how long, electrically, the coax is with respect to a half wavelength. For coax with lengths that are even multiples of quarter wavelengths, 2/4, 4/4, 6/4 etc, the transformation comes full circle and whatever the antenna impedance is is what the coax input will be ~ which is why people like using half-wave coax cables for tuning antennas. If you were trying to measure the R±jX of an antenna and the coax is not an even multiple of quarter wavelengths, you need to either do an OSL calibration or mathematically account for the transformation of the coax you're using. [side rant for VNA/RigExpert users: This is why people connect their nanoVNA's directly to the antenna without coax. I disagree with the practice because it puts the analyzer, and the person reading it, directly in the near field and screws up the reading. Either use a half wave coax or do an OSL cal, I promise it is worth your time]
Here's where it gets tricky. As I said before, if we connect a length of coax (that's not an even multiple of quarter wavelengths long, 1/2, 2/2, 4/2 etc) to a mismatch, the coax transforms the impedance. But whether it changes the SWR or not depends on the characteristic impedance of the coax. If the coax is perfectly 50Ω and that is connected to a mismatch, the complex impedance looking into the coax changes based on coax length, but the SWR seen by a 50Ω source will not. Any reduction in SWR is a result of the coax loss attenuating the reflected signal. However, if the coax is not 50Ω, it's length will not only change the impedance, but the SWR also changes as we are no longer rotating about a circle centered on the middle of the smith chart. This is why we are able to use 75Ω coax to transform impedance to a different absolute value, something that coax with a characteristic impedance matching our source cannot do.
That said, there are reasons to change the length of the 50Ω coax to the radio:
One example might be where there is a mismatch at the antenna and the impedance looking into the coax is at a point your particular tuner cannot handle. For example, if the impedance looking into the coax is 12-j15, an L match consisting of a variable shunt capacitor and variable series inductor (with the coax on the shunt side), there is no combination of reactances that can match 12-j15 to 50ohm. However, if you make the coax longer by 1/4 wavelength, the impedance becomes 82+j100, which the matching network can easily be tuned to. 12-j15 and 82+j100 both have the same SWR as seen by a 50Ω source, but only one can be tuned with the tuner I mentioned. Another example is phasing of antenna elements.
Yet another example is to change the electrical length (thus impedance) of the shield which common mode currents travel as this can have an impact on SWR if the coax shield happens to be acting as part of the antenna.
Passed by that shop a few thousand times pulling loads out of Granite City but never went in. Heard lots of good things about the shop though from all the locals.
Well, it'll take a few minutes, or days to chew on all that. Thanks for the info.
Probably confused about the 50Ω ohm coax to route FROM THE TEE - to the radio.
- PDL2s - any beam antenna - will use a method of a different ohmic coax - they call a harness - to get the antennas SWR to look right so someone could then hook up a simple 50Ω coax to get it back to the radio.
When you split a signal - transmitting it or receiving it, you have to "make it right" by offering a means to "share the load equally" between the spots you want to use.
Notice too, that as the spacing changes, so does the Wave patterns, the cancellation and augmentation - Nodes and Anti-nodes change and affect how that pattern "works" within itself.
So, the phasing issue if it's correctly handled - that RF signal speed (propagation) is still the same, just the placements are needing to be pretty close to one of those "nodes" - to make the patterns work and to also keep the SWR right.
So once the antennas are spaced right thru the harness - any 50 Ωohm coax from that center point tee, will make it far more convenient for the operator to get the radio connected to this type of antenna.
2 antennas? Split it in the middle - so use 75Ω to split between the signal between the two antennas - then meet them together (combine), then any 50Ω coax from that split / combine point back to the radio - should do just fine.
Another technical explanation to chew on. Good stuff. Thank you. I noticed my SWRs dropped from 2.0 to 1.5 when going from a single 50 ohm coax, to the 75 ohm cophase. Normal? T680s are awful to get good ground, and low SWRs.Probably confused about the 50Ω ohm coax to route FROM THE TEE - to the radio.
You are correctly using the 75Ω - co-phase - in the harness FROM BOTH ANTENNAS TO THE TEE - as @AudioShockwav did a nice job of - its the correct way to go...
- PDL2s - any beam antenna - will use a method of a different ohmic coax - they call a harness - to get the antennas SWR to look right so someone could then hook up a simple 50Ω coax to get it back to the radio.
Got a Protractor and an Architect Compass - let him borrow it and send him off to a restaurant that offers a table and placemats - and let him play with them. Sooner or later, he might do up something like this...
.
When you split a signal - transmitting it or receiving it, you have to "make it right" by offering a means to "share the load equally" between the spots you want to use.
Notice too, that as the spacing changes, so does the Wave patterns, the cancellation and augmentation - Nodes and Anti-nodes change and affect how that pattern "works" within itself.
So, the phasing issue if it's correctly handled - that RF signal speed (propagation) is still the same, just the placements are needing to be pretty close to one of those "nodes" - to make the patterns work and to also keep the SWR right.
So once the antennas are spaced right thru the harness - any 50 Ωohm coax from that center point tee, will make it far more convenient for the operator to get the radio connected to this type of antenna.
2 antennas? Split it in the middle - so use 75Ω to split between the signal between the two antennas - then meet them together (combine), then any 50Ω coax from that split / combine point back to the radio - should do just fine.
Slowpoke: Been following the exploits of this. I stay out because it's been 30 years since did work on Big Truck antennas.
Then it was West Coast Stainless steel mirror frames and real metal on most cabs.
That said, is there any way to give us pics of this set-up you're working with?
There has been so much convoluted info just in that one post, I truly have gotten lost to what you are truly doing or trying to accomplish. Thus, what equipment antennas/switches /harness(s) are now in actual usage.
FYI just trying to help, after 50+ years in radio land. I understand the frustration of dealing with issues, when info is contradictory from several sources.
All the Best
Gary
Then it was West Coast Stainless steel mirror frames and real metal on most cabs.
That said, is there any way to give us pics of this set-up you're working with?
There has been so much convoluted info just in that one post, I truly have gotten lost to what you are truly doing or trying to accomplish. Thus, what equipment antennas/switches /harness(s) are now in actual usage.
FYI just trying to help, after 50+ years in radio land. I understand the frustration of dealing with issues, when info is contradictory from several sources.
All the Best
Gary
Yes, and will go even lower - once you take care of two things...
One - counterpoise...the antenna itself is only 1/2 of the whole radiator, so when you use two - you still are only using 1/2 the effort - split - now into two. It's why some drivers say "To h*ll with it" and just run one antenna - it's easier and simpler but the image and the counterpoise where the thing radiates from and towards - is not the best (off the opposite side).
Second? The spacing - not as critical as counterpoise and grounding but needed so you can properly make the "image" from the truck - but look above in the post, have the tech stare at the image for a few hours - then send him to the truck stop and have them supply him with plenty of placemats and even crayons to help fill in the missing pieces of this puzzle and maybe several others he never finished earlier in his life.
As you get older, I can see a lesson forming - where it's wise to always get a second opinion if possible - may not provide the best possible info - but then you didn't have to stop at just a #2 - go all the way until your satisfied...
It's sad that the segue into retirement is showing evidences of a medical condition you don't want to deal with in this scenario. To have that much background and experience - then to tell you this - hurts...more than you know.
One - counterpoise...the antenna itself is only 1/2 of the whole radiator, so when you use two - you still are only using 1/2 the effort - split - now into two. It's why some drivers say "To h*ll with it" and just run one antenna - it's easier and simpler but the image and the counterpoise where the thing radiates from and towards - is not the best (off the opposite side).
Second? The spacing - not as critical as counterpoise and grounding but needed so you can properly make the "image" from the truck - but look above in the post, have the tech stare at the image for a few hours - then send him to the truck stop and have them supply him with plenty of placemats and even crayons to help fill in the missing pieces of this puzzle and maybe several others he never finished earlier in his life.
- He is correct in his thinking - but if he's not putting it together right...
As you get older, I can see a lesson forming - where it's wise to always get a second opinion if possible - may not provide the best possible info - but then you didn't have to stop at just a #2 - go all the way until your satisfied...
It's sad that the segue into retirement is showing evidences of a medical condition you don't want to deal with in this scenario. To have that much background and experience - then to tell you this - hurts...more than you know.
It started as a mere observation and experience gripe. It morped into explanations to help me understand antenna theory. I'm just looking at either the best as for both tx/rx, in most directions, whether cophase, or single, and whether center load cup or coil, or top load. I was merely trying an experiment with the antenna switcher, to see which type of antenna worked best, or if one antenna worked better one day, or condition, but the other better another day or condition, such as a top load skip shooter, and a center load w2k or predator 10k. The switcher however, doubled my SWRs whether hooked to a 3' jumper, or the stock 10-12" jumper on back of radio. I drive a T680, which many cb shops don't like working on, due to style of mirror mount, and grounding. That's it.informative I appreciate all the info, but it goes beyond my simple needs, and experiment. The info is informative nevertheless.
