Swr meter for UHF/VFH?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by DOCD, Feb 22, 2015.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: Left-3
ad: Left-2
ad: L-MFJ
ad: MessiPaoloni-1
ad: Subscribe
  1. WA9SVD

    WA9SVD Ham Member QRZ Page

    I'm not sure you understood the "Tech question" properly. There's very little difference between "N" and "properly installed, good quality, UHF" connectors at 2 Meters, and in most cases, on 70 cm, and much commercial and Amateur equipment still use UHF connectors through the 70 cm range. Above that, there is a concern about maintaining a constant impedance through connectors, which the UHF series does NOT provide. At or below the Amateur 70 cm band, there is little advantage to using type "N" connectors, save for the inherent "weather-proof" assembly of most (but not all) type "N" connectors. (At least, those with Mil-Spec UG-21xxx designations are supposed to be highly weather resistant.) It certainly won't hurt to use "N" connectors, but the co$t/advantage ratio usually makes the cost greater than any advantage gained, at least through 2 Meters, and even 70 cm.
    Above 70 cm (~450 MHz) I wouldn't use UHF connectors, regardless of purported quality; I would use only "N" connectors, but again, properly installed, and from a known, quality brand. (Such as Amphenol, Kings, or a few others.) "Cheap" import "N" connectors may be worse than using UHF connectors above ~100 kHz...
    Connectors are a dear part of your installation, and can be a bear to replace if they fail; don't try to scrimp and save a couple of $ on inferior coax connectors of ANY type. One trip up a tower, in the dead of winter, will make you wish you hadn't saved a couple of $ on inferior connectors.

    BTW, I'm a certified ARRL "Instructor," and I can't find any part of the Tech OR General question pool referring to a "NEED" to use type "N" connectors, at least not on 2 M or 70 cm. I personally have equipment through 1.2 GHz, and the only time I feel a NEED to use type "N" (or BNC for low power) is on 1.2 GHz; I don't find good quality "UHF" connectors are unacceptable even at 70 cm. I certainly wouldn't modify any of my equipment just to accommodate type "N" connectors, although I might use them (due to weather resistance) if I were constructing my own equipment or antennas, but then, only on bands above 2 Meters.

    As far as coax is concerned, your best bet for runs under ~100' would be a version of LMR-400; there ARE good equivalents made by Belden, as well, if properly installed. If you are installing a vertical antenna , then standard LMR-400 will be adequate. If you are anticipating using a rotatable antenna, they you would need at least a short section of more flexible cable (Such as LMR-400UF) to allow for the movement of such an antenna; the standard LMR-400, or many versions of Belden 9913 are quite stiff, and would not allow for rotatability.
     
  2. WA9WVX

    WA9WVX Ham Member QRZ Page

    Here's my thought about the UHF versus the N type connectors, hands down I'll take N type connections any day because they are a constant impedance from low frequency right up through the microwave bands and using the Amphenol type N connectors, you will not have any impedance bumps in your Feedlines. Yes, they take a little more effort to properly learn how to install but once you do a couple connectors the rest will become a breeze. These fitting if done correctly are almost impossible to pull apart, I've done hundreds of them in the commercial land mobile two-way radio field. For VSWR Bridges I tend to lean to a Bird 43 Wattmeter with the correct slugs that cover the 144 MHz and 440 MHz bands since this Wattmeter is the industry's standard and you can get any combination of RF connectors for the these wattmeters, N-Male, N-Female, UHF-Male, UHF-Female, BNC-Male, BNC-Female, DIN-Male or DIN-Female oe any combination of these connectors plus you'll own an industry standard instrument that you can depend on. I've used the Telewave Product in the Land Mobile Radio Industry and they are so inaccurate that if someone gave me one, I'd throw it in the garbage not worth the frustrations to pass it to anyone else. Coaxial Dynamics makes a very good wattmeter equivalent to a Bird 43 wattmeter and the RF sensing slugs are interchangeable.

    My recommendation for good base station antenna is a Comet GP-9N, it's 17 feet tall, OMNI Directional with +6 dB Gain (4 times the RF Power that reaches the Antenna) on 2 m and +9 dB Gain (8 times the RF Power that reaches the Antenna) on 70 cm and you'll be able to hear the close in or farther away signals. I've owned one for 3 years now and it's side mounted on tower at 80 feet, with only 10 W I can have regular QSOs 90 to 100 air miles away ... height is a major factor on VHF and UHF ... Oh, I should mention that I spend most of my time on Simplex rather than Repeaters. The GP-9 antenna is rated at 200 W maximum and I've never used more than the basic 10 W out of the transceiver but I do have a RF amplifier capable of 750 W output which would probably blow this antenna apart.

    Now lets consider the coaxial cable or feedline between the transceiver and the antenna. The minimum coaxial feedline I will recommend is LMR-400UF (Flexible) for using on an Omni Direction or Yagi Beam antenna. This feedline provide a much lower loss than the typical RG-8/U, RG-213/U, RG-8X, 8214 or the RG-58A, B, or C type coaxial cables. There are better coaxial cables and they are known as Andrews Heliax, LDF4-50 1/2" Heliax has .9 dB Loss Per 100 feet at 144 MHz and 1.8 dB Loss Per 100 feet at 440 MHz and I believe you gave the figure of 60 feet which would reduce the insertion Loss down to .55 dB or 12% would be lost in the cable at 144 MHz and 1.1 dB or 22% would be lost in the cable at 440 MHz versus LMR-400UF at 60 feet would be 1 dB Loss or 20% would be lost in the cable at 144 MHz and 1.8 dB or 36% would be lost in the cable at 440 MHz and lets look at RG-213/U at 60 Feet would be 1.5 dB or 30% would be lost in the cable at 144 MHz and 3.12 dB or 52% would be lost in the cable at 440 MHz. Doc I hope you are understanding how important good coaxial cable is for your transceiver to be heard and how well the receive signal is heard on your end. You can contact a local business band radio shop or tower company and purchase Used LDF4-50 for 75 Cents Per Foot and the N Type connector for $5 to $10 each. Use nothing less than 3M Electric tape for all of the RF Connectors and you may want purchase a can of Scotch Kote, it can be found at Home Depot and Lowe's. Apply the Scotch Kote over the 3M tape to insure waterproof connections outside.

    Good Luck on your Decisions

    Dan
    WA9WVX
     
  3. K8ERV

    K8ERV Ham Member QRZ Page

    Yeah, but it is difficult when you already know it all.

    TOM K8ERV Montrose Colo
     
  4. KC3AZG

    KC3AZG Ham Member QRZ Page

  5. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    I occasionally clear out the memory to make room for new stuff. Now where did I put my name?,,,,,
     
  6. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    I have an ancient MIDLAND CB SWR bridge that works great even at 2 meters. I don't know if they were all like this, or I just lucked out.
     
Thread Status:
Not open for further replies.

Share This Page