ANTENNA Tuner Correct Specs But Misleading

Discussion in 'Ham Radio Discussions' started by KC3EPA, Apr 15, 2018.

ad: L-HROutlet
ad: l-rl
ad: FBNews-1
ad: L-MFJ
ad: Left-3
ad: Left-2
ad: Subscribe
  1. KC3EPA

    KC3EPA Ham Member QRZ Page

    I also tried the alligator clip trick years ago
    I had to use 2 at a right angle when windy.

    I have since added a coil for 40 meters at base.
    It works great and tunes out the capaciive reactance of a shortened antenna

    I did strap to a area on chasss
    You are right thee
    Is not the best continuity of trunk lip with rest of vehicle with just a couple of bolts
    I have straps going to the frame in wheel compartment.

    Thank you for your input.
  2. KB9BVN

    KB9BVN Ham Member QRZ Page

    A dummy load will match across all bands. It radiates very poorly. A good match to a bad radiator, isn't going to radiate well...but at least it won't damage your radio...much.

    You ought to get a better antenna if possible. When I ran HF mobile I had a 3 pack of hamsticks. 20, 30, and 40m . When I wanted to change bands, I pulled over, swapped antennas, returned and was back on the air.

    Have fun and good luck.
  3. KC3EPA

    KC3EPA Ham Member QRZ Page

    Yes that is true that is why 7 foot hamstick work but are very inefficient at 80 and marginal at 40.
    All they do is take a shortened antenna that is capacitive and use an inductor to cancel capacitance for match.
    A 16.5 foot antenna on 20 meters will put any 20 meter hamstick to shame.
    I now have a matching coil for 40 and it is much more efficient than hamstick

    An antenna tuner is basically a t network that adds inductance when antenna is short and required reactance when long.

    Getting out and swapping is always an option.
    I must want longest antenna possible that can be safely placed on car and is now resonant on 20 meters and if need be 40 meters by moving alligator clip Detroit
  4. KC3EPA

    KC3EPA Ham Member QRZ Page

    Google voice is on for typing and the word Detroit was picked up.
  5. KK5JY

    KK5JY Ham Member QRZ Page

  6. WZ7U

    WZ7U Ham Member QRZ Page

    Well, don't say Detroit. ;)
  7. N4UP

    N4UP Premium Subscriber QRZ Page

    It seems to me the objective is to radiate power effectively and efficiently in a mobile ( compromise ) setting. Aside from short cables, good coax, proper "grounding" etc., one approach is to use a good screwdriver antenna with capacity hat, which can be remotely ( and depending on the controller, automatically ) adjusted to minimal SWR. The only problem I see with a screwdriver is lack of precision in that adjustment. In my experience, on 10-30 meters that is not a problem. On 40-80 meters a "best match" may just be between "turns" so you can get close, but not quite there. Granted SWR is not the end-all, but I have no problem getting my screwdriver quickly adjusted to less than 2:1 SWR and usually closer to 1:1 so I don't need a tuner. But the SWR at any given antenna adjustment can vary a bit, as weather conditions change or if there is coupling with something nearby ( memo to self: do not park under a power line and raise/position the antenna for operation on 80 meters ).

    So what I do is have the MFJ-998 auto-tuner which I engage to get the best match if the screwdriver length is off just a little bit, means I don't have to waste time re-adjusting the antenna. Why? Because I typically make several band changes in every county I pass through. I have two SWR meters, one on the antenna side showing the "actual" antenna SWR and the other in the auto-tuner showing the "matched" SWR. I make sure the "actual" SWR is good before I engage the tuner. I say "actual" and "matched" because I don't know that any SWR meter is very accurate, but they give "indications" of SWR.

    So why do I adjust the match even if it starts at less than 2:1 ? Because I run a solid state amplifier in the ( pickup ) truck, typically at 200-500 watts. The amp prefers lower SWR.

    I have not measured the efficiency of my mobile "system" but I infer/suspect it is fairly good ( for mobile ). Last year I made over 8,000 mobile contacts on HF, mostly on CW.
    NE3R likes this.
  8. WA9SVD

    WA9SVD Ham Member QRZ Page

    A Dummy load should present a low or immeasurable SWR for the frequencies for which it is designed. ( A Dummy load for 160 M is not necessarily good for 70 cm.) MOST dummy loads also present little, or no radiation, hopefully far less than just "poorly, or even "very poorly." YMMV, of course.
  9. KB9BVN

    KB9BVN Ham Member QRZ Page

    Man that sounds so familiar.

Share This Page