What are HT antennas 'tuned' against at the factory, and why do people use HT 1\4 waves?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by FISCOKING, Sep 15, 2020.

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  1. FISCOKING

    FISCOKING QRZ Member

    Hi,



    I was looking for a better antenna for my 2M HT (Vx-120) today and ended up on the Nagoya and Diamond websites. Nagoya has more technical info than Diamond. I'm aware that A and E have many fakes, and that I have to shop via an authorised dealer. No issue there.

    In the 40cm (ish) bracket, both manufacturers have many options, and the antennas are described as 1\4 wave at 2M and 1\2 wave at 70cm. The two antennas below seem quite popular. E.g.

    Diamond

    RH771: 144/430MHz(2m/70cm)
    Length:40cm / Weight:42g
    Gain:2.15dBi(430MHz) / Max.rating:10W FM / Impedance:50ohms
    Connector:BNC-P / Type:1/4wave(144MHz),1/2wave radialless(430MHz)
    (http://www.diamond-ant.co.jp/english/amateur/antenna/ante_3hand/ante_hand1.html)

    Nagoya
    NA-771 Frequency : 144/430 MHz
    Gain : 2.15 dBi
    Length : 39 cm
    VSWR : Less 1.5:1 Impedance : 50 ohms
    Connector : BNC/SMA Male/SMA Female
    (https://www.nagoya.com.tw/en/product-384799/NA-771.html)
    (https://www.nagoya.com.tw/v_comm/in...lang=2&id=384799&file_name=p_160325_07186.pdf)

    Two questions arise from the above information:

    1. Given that a HT antenna is only half of the antenna system (the bottom half being the HT chassis ground), what do they test against when coming up with these gains and SWR readings?
    a) Another identical opposed antenna (that's makes a dipole).
    b) Some 'industry standard' model of a universal HT antenna body?
    c) Nothing other than the metal body of the analyzer that's taking the readings - which makes the size of the analyzer important?

    2. At 2m (145MHz), why would anyone want a 1\4 wave antenna on their HT - as a 1\4 wave needs an artificial ground or matched lower radiating element (making it a dipole) in order to work correctly? The SWR of a 1\4 wave HT monopole attached to a much shorter HT body to radiate against is very high. See below. I made a 4NEC2 model of the UV5R body attached a 52cm element at 144MHz over an average ground @ 1.8m. SWR=26. This doesn't account for capacitive coupling to a human body though.

    [​IMG]


    I'm aware that many recommend the use of a 'tiger tail' counterpoise to improve reception on HTs, but all this is really doing is creating the lower leg of a dipole. Why would an aftermarket antenna manufacturer create a 1\4 wave HT antenna that needs a tiger tail to operate correctly - and then not tell you about it.

    I'm missing something here, or perhaps I'm meant to be reading the spec sheet and 'deducing' that I need to add a ground plane or tiger tail - in which case why are 1\4 wave antennas marketed as HT antennas(?)

    Is this some new definition of marketing?

    The above antennas already have matching networks in them, so why don't they match the antenna to the shortened HT chassis? This is also possible according to 4NEC2. The sim below shows the same 1\4 wave monopole with a T match network (2 inductors and a cap) and the SWR comes down to <1.1.

    [​IMG]

    I'm guessing that as they don't know the HT chassis dimensions, they just tune the matching network to something else...or maybe they do try and match it to a 'standard' HT chassis but they don't tell us what that is.

    I'm not the only one that's noticed 1\4 wave HT antennas offer high SWR. The review below by Craig McVeay (N0CSM) sheds some light on this. He uses a field strength meter to check the radiation on a Yaesu rubber duck and a Diamond, with and without a tiger tail. The Diamond performs much worse than that stock Yaesu, both without the tiger tail. The Diamond out performs the lot with the tiger tail.



    At a guess, I'd say the Yaesu ducky performs better on its own because Yaesu actually matched it to the HT that they also made and shipped it with, whereas Diamond didn't - they just made a standard 1\4 wave.

    A lot of the HT antennas hide behind marketing and branding, so any further insight is appreaciated.

    Thanks.
     
  2. AI3V

    AI3V Ham Member QRZ Page

    You are way over thinking this, and not to hurt your feelings but your "model" is useless.

    My background.

    I have fixed a few thousand ht's

    Yes, several thousand :)

    Your hand has more than enough coupling even at 2m with a uv5r to provide a perfect "other half" of the antenna.

    The ht has a nominal output impedance of 50 ohms.

    The ht antenna should have a similar impedance.

    For the most part NO professional ht users use a full 1/4 wavelength whip at vhf, the length is inconveniently long, and likely to damage the antenna connector.

    At uhf, full 1/4 wavelength flexible whips are sometimes used.

    As to how the manufacturer "tests" whips and comes up with a "gain" figure? Probably mostly by letting the advertising department pick nice numbers out of thin air.

    At the shop we used a simple field strength meter, as it is often impossible to tell wether a whip is low vhf, high vhf, or uhf by visual inspection.

    Many low vhf (30-50 Mhz) whips were only for 10 Mhz or so, and had a ferrite slug in them that could be adjusted.

    Vhf hi (130-170Mhz) and uhf whips never had tuning provisions other than cutting a long ducky to increase the resonant freq.

    "Tiger tails" are unknown in the professional world, they are strictly a sammy hammy plaything.

    The most common repair I did was replace damaged antenna connectors, I NEVER replaced a "final" on a professional ht.

    Ham ht's, THAT ARE USED WITH BATTERIES OTHER THAN THE BASIC STOCK VOLTAGE BATTERY , OR "BATTERY ELIMINATORS" IN A ATTEMPT TO OBTAIN MORE POWER destroy finals regularly.

    Rege
     
    K3RW, WN1MB, US7IGN and 1 other person like this.
  3. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    Well a lot of work way put into the presentation and testing, but the setup was completely different from what I'm sure the original antenna designers used. It would make sense to design the antennas for low SWR when used normally: this would be with the antenna on the HT, the HT held in the hand, and the TX happening with the HT held up to the head or attatched to the body with a belt clip. Change any of these things and the SWR will be completely different. So even though the presenter did a lot of effort, it was basically worthless for the average user. The setup added extra coax, extra material being the analyzer, and I'm pretty sure the tester didn't have the antenna positioned near his head or body as it would be in normal operation (maybe he was, but I didn't watch the whole video). So what he was optimizing for these antennas was, "How to get low SWR and tune an HT antenna while it is connected to extra coax, an analyzer, mounted on a bracket on a piece of wood."

    73, Mark
     
    KA0HCP likes this.
  4. N7EKU

    N7EKU Ham Member QRZ Page

    Also,

    Probably the best way to check HT antenna SWR would be to build a very small stripline meter that can be attached between the HT and the antenna. It could be made pretty small for use on 2m and have a low affect on the system.

    73, Mark
     
  5. K9ZMD

    K9ZMD Premium Subscriber QRZ Page

    What does a factory use to tune a rubber ducky? Dunno, but you're probably asking the wrong folks unless it happens there's a factory wonk aboard.

    Why do hams use 1/4 wave antennas? Mostly because hams sometimes want (or even need) to work simplex and the simplex range of a rubber ducky really sucks. In contrast, a 1/4 wave radiator on a handheld radio has remarkably greater simplex range. Maybe "remarkably" even understates the improvement.

    Even though a handheld's frame and hand capacitance can compensate for the "missing" half of the antenna, a tuned counterpoise (a so-called tiger tail) often improves reception at the fringe of simplex range . . . even if a 1/4 wave radiator is installed. I've experienced this while hunting in Wisconsin's north woods where a dozen yards can make the diff between solid reception and "just noise". (Tiger tails may improve the transmit signal, too, but I've never tested that). So, hams choose to use a tiger tail because - just as with 1/4 wave radiators - they sometimes do want or need to communicate with very weak fringe signals and the tiger tail can make the difference between "just noise" and an understandable signal.

    As for impedance mismatch, if a handheld expects a 50 Ohm load, then a 1/4 wave's ~32 Ohm impedance is not far enough off the mark to cause a modern handheld to fold back power.
     
  6. AI3V

    AI3V Ham Member QRZ Page

    There is no "foldback of power".

    The impedance "seen" by the tx is constantly changing with the position of the radio.

    For 1/2 of all possible impedance mismatches the power output goes up.

    Limiting the voltage to the final by using a stock battery is how you prevent final transistor damage.

    Again, we "tuned" antennas with a simple field strength meter, nothing but a meter and a diode.

    Quality ht's (and other quality transmitters) protect the final transistor by picking a transistor that will not be damaged by vswr. (When powered with stock battery)

    Open, short, sitting on the rig, it dosn't matter, the transistor is immune to damage.

    A typical 25 watt commercial radio uses a final that would be pushed to 75 watts in ham service. Its the sane difference between the 2 litre motor in your car, and the same displacement engine in a race car. One lasts 200,000 miles, the other might make it 2 hours.

    Rege
     
  7. FISCOKING

    FISCOKING QRZ Member

    Thank you for your replies.


    "not to hurt your feelings" > No worries. ;). I don't mind people disagreeing when they add an explanation. The differing opinions are why I come here. Your point about burning up finals with battery eliminators and non-stock batteries is new to me. Learned something there.


    HT antennas are definitely and art. No question about that, and that's why I'm interested. The one large part of the jigsaw puzzle that's missing in the simulation is the person holding the HT. I posted a question on the 4NEC2 forum asking about models for people and cap. coupling but didn't get a reply. The only research I can see on this subject after some searching is for mobile phone radiation absorption. All the data from this is in the microwave region.


    Without a very elaborate analyzer set-up for HT antenna measurements (and I have some ideas on that topic), I've come to the conclusion that the easiest and cheapest way for a Ham to test 'your new' HT antenna is with a field strength meter mounted some distance away with another person taking note of the readings. The meters are cheap (MFJ make one) and offer a relative comparison. I had hoped to use an antenna analyzer but after much though and some field testing, they introduce a whole new set of variables (with HT antennas) that skew the results unless you're very careful with the test set-up. You'll get an analyzer reading, but it won't necessarily be the same one that your HT sees.


    Anyway, 73's.
     
  8. DO1JML

    DO1JML Ham Member QRZ Page

    I checked a few handheld whip antennas with a nanoVNA. The ones which worked (a cheap copy was not internally connected, which is the reason why I used the nanoVNA) were not tuned to the correct frequency unless I held the nanoVNA in my hand. It seems that the manufacturer correct for the effect of the user's hand.
     
  9. KX4O

    KX4O Ham Member QRZ Page

    For what it's worth, we did real EiRP tests in a chamber using a Yaesu FT-1D in APRS beacon mode (no wires or humans touching it) with stock and some aftermarket antennas along with the effect of the dreaded tigertails...
    The approx. 1/4 wave variation was the most troublesome. The stock antenna was surprisingly good despite its short stature. Other less accurate listening tests confirm Rege's point of a need to hold the HT to make the most of the 1/4 wave aftermarket HT antenna offerings.

    Note I make the claim the HT lowers power in high SWR situation, but if Rege is correct in that these radios don't roll back power, then the power loss revealed in the EiRP measurements is entirely due to mismatch loss between the radio and antenna. The measurements cannot distinguish between the two... it only shows the effective result.
     
    Last edited: Sep 17, 2020
  10. K5EMG

    K5EMG XML Subscriber QRZ Page

    Unfortunately my in the field results are different. I have a Yaesu FT3D HT and the stock antenna sucks, bought the Diamond and RX/TX gained from it. Maybe the FT3D antenna is not matched as well than the FT1D. Even the SWR are worse when compared with the Diamond, not for too much. The radio itself has a poor rx sensibility, compared to my VX-6R.
     
    KX4O likes this.

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