hbg6@citek.mcdphx.mot.com (12/12/90)
In article <12765@milton.u.washington.edu> amigo@milton.u.washington.edu (The Friend) writes: > > I'm wondering if some gizmo like that of the rabbit ears's "dial" > that helps pull the signal in exists for outdoor antennas as well.. > Seems like this could be the key to locking the station in or not. > Now that you mention it, I've always wondered what that knob on the antenna actually did. I guess it might rearange the phasing between the 'ears', anyone out there know for sure? John
billn@hpcvaac.cv.hp.com (bill nelson) (01/01/91)
depolo@eniac.seas.upenn.edu (Jeff DePolo) / 9:04 pm Dec 16, 1990 / writes: >> b) Terminated it poorly or are using the wrong impedance cable >> (you'd better be using 75 ohm coax (not 50 ohm!) or 300 ohm twin >> lead). >You'll realize little difference between 75 ohm and 50 ohm coax. When >you consider what a wide range of frequencies you are attempting to >receive, even with a well designed log periodic, the feedpoint >impedence is going to vary over quite a wide range. Choose the cable Absolutely correct - I believe the primary cause of the impedence variation is due to mounting height variation. I know the effect decreases as the height (in wavelengths) increases. I don't think the 25-40 ft above ground level is enough to minimize this factor. Bill
tad@ssc.UUCP (Tad Cook) (01/03/91)
In article <6690003@hpcvaac.cv.hp.com>, billn@hpcvaac.cv.hp.com (bill nelson) writes: > > Absolutely correct - I believe the primary cause of the impedence variation > is due to mounting height variation. I know the effect decreases as the > height (in wavelengths) increases. I don't think the 25-40 ft above ground > level is enough to minimize this factor. Maybe at HF, but at VHF 25-40 feet above ground without nearby obstructions should be just fine for minimizing impedance variations. I have seen charts in the ARRL Antenna Book which shows impedance variation based upon height above ideal ground, and they are talking about at a wavelength or less. One wavelength at lowest frequency (TV ch2) is something around 17 feet. Tad Cook Seattle, WA Packet: KT7H @ N7HFZ.WA.USA.NA Phone: 206/527-4089 MCI Mail: 3288544 Telex: 6503288544 MCI UW USENET:...uw-beaver!sumax!amc-gw!ssc!tad or, tad@ssc.UUCP