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Author Topic: Screwdriver vs. SGC 9 ft Whip/Tuner Combo  (Read 11270 times)
W5DXP
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« Reply #30 on: October 17, 2010, 10:02:10 AM »

Interesting data, Cecil, but you don't give any measurement methodology..

The power to the antenna was measured using two Bird directional wattmeters. Power to the antenna equals forward power minus reflected power. The signal was measured in the far field with a ferrite loop antenna tuned to the test frequency. It was done by some very competent RF engineers from the LA area using a very accurate RF voltmeter.

Quote
I think the antenna tuner losses are smaller than everyone is claiming.
I haven't measured the loss, but here is the measured feedpoint impedance for my improvised dual resonance whip:

How does your whip exhibit a dual resonance on HF? Do you have a loading coil there somewhere? Everything I have said about the SGC+whip assumed a standard CB whip resonant on 11m or the 11.5 whip, resonant on 15m, that was used for the measurements.

Quote
So it looks, at first glance, like the loss in the tuner is going to be less than a dB.

The measured difference between a base-loaded bugcatcher and an SG-230 with 11.5' whip is 7 dB. I don't see how that 7dB could be anything other than losses in the SGC tuner. Where else could that 7dB of loss be occurring?
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K0BG
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« Reply #31 on: October 17, 2010, 10:30:00 AM »

As I stated previously, part of the loss is the whip itself.

It is interesting to note, that if you take the data from the ARRL Handbook for a 10.5 foot antenna, at 3.5 MHz, the resistive component is 7.43, and the reactive component is -j1375. If you plug this into the T match simulator, you can't get a match! The fact the SGC will match this load, has got to tell you something about the internal losses.

Once upon a time, I used a 13.5 foot, 20 meter resonant, center loaded antenna. It was driven through a SG235. The losses on 20 meters were virtually nil. On 40 meters, it appeared to work well although I zapped a few relays over time. On 80 meters, the 235 would only match the setup in a few segments of the voice sub band, and not at all below 3.650. With just 100 watts, the 235 got warm enough to feel the heat. Scared me enough, that I never used the amp on 80 or 40!
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K8KAS
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« Reply #32 on: October 25, 2010, 11:43:56 AM »

Look at the really good mobile signals on the band, they don,t run Wilson CB toys they run BIG antennas with good bonding to the vehical body, the SGC with a tuner is OK on 20 meters and up with good mounting/up hi and good RF grounding But on 40 M and 75 M the thing is (a dog) down 8 to 15 db from a good Texas BugCatcher. My buddy WN8W picked up 10 db on 75M going from the SGC whip/Tuner to a simple Hustler mast and KW coil. I would like to add as someone also mentioned don't believe a word about performance if it's from the builder of the product, see the reviews on EHam and read about what real users say about the product, Or pick up a good calibrated RF field strength meter and do some real field testing, it is not hard to do, constant carrier power and 4 or more points 360 deg over a measured distance and you can see very quickly what antenna has the best signal. PS it's fun as well.
I used to run the Tarheel T200 (1500) watt model with a 6 foot whip and top hat, I thought it was a ruff antenna to beat, but as I said it was BIG but I loved it, no tuner needed and I could tune 75M Thur 10M with the antenna. IC 706 MK II and I could work anything I heard with great reports.
73 Denny K8KAS
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