AM Radio

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    Andy Brown

    If memory serves, they dismantled one and went to 500 W non directional at night from the remaining tower. Then used the new tower in the same way to take down the other tower. Probably some hours off the air at midnight to do all the plumbing necessary to make that happen. Not sure if it was 500 W but that is usually the authorized power for a 5 kW DA-N to operate in the non directional mode. Been there.


    That certainly makes sense. I’m sure Craig knows what power KGW ran at night before going directional. It might have been 1KW and if that’s the case, maybe that’s what they ran in ’78.


    KGW night power was 1kw non-directional from April 5, 1926 to December 25, 1941.

    June 1, 1948 Tuesday – The Oregonian – KGW RESTORED AFTER 14 HOURS

    Radio station KGW was back on the air at 7:30 a. m. Monday, operating through KALE’s spare transmitter on Mt. Scott, approximately 14 hours after one of its flooded transmitting towers was toppled by a floating house. Manager H.Q. Cox said engineers worked all night to tune the transmitter to KGW’s frequency. The spare KALE facilities have been offered until repairs can be effected, he said. No estimate of the amount of damage was available.

    June 25, 1948 Friday – The Oregonian – BEHIND THE MIKE

    KGW has received delivery of a brand-new General Electric transmitter, which it has installed on its Healy Heights property [KGW-FM] and will begin operation on Saturday. Since KGW’s regular transmitter and one tower were lost in the flood, the station has been operating on a set owned by KPOJ. The new transmitter, which was purchased for temporary use, will be maintained on the Heights as a standby plant, even after the flood waters recede and KGW installs a new transmitter and erects a new tower on its old site in North Portland.

    Matt Jones

    Scott Young made mention about the real estate value of transmitter sites. Specifically, KEX/KPOJ. I can’t say I know all of the specifics, but I do recall an event about a decade ago. ODOT approached Chear Channel with the intent to buy the Clackamas TX site as an easement for the Sunrise Corridor during its planning phase. This, along with a portion of Camp Withycombe, would have given the project a much more direct path than what has eventually been decided upon.

    ODOT eventually decided not to persue the site for financial reasons, in part. It was going to cost the state far too much to relocate the contents of the site to a comparable location. One that would not create a hardship for the station(s).

    But the primary reason ODOT passed on the site – and what will more than likely make it unsuitable for any reasonable future development – is that it’s a federally protected wetland. The transmitter site is Grandfathered in place, since the wetland status wasn’t known in the 40’s, when the site was constructed. If ODOT had proceeded, they were going to have to build the roadway on piers, to disturb as little of the area as possible.

    Dan Packard

    Regarding the old AM 620 KGW radio towers that were west of what is now Delta Park and I-5, they show up in this air photo from 1945,

    The picture is grainy on magnification. It looks like two tall towers soaring skyward to the same height of the airplane taking the picture, and a shorter tower equally spaced to the north.


    Magnify upper left hand side of photo.


    “Aug 2, 1931 moved its transmitter & towers to North Denver Ave. in North Portland. 300 foot flat top towers.”

    So in the 1945 picture we are seeing the 1937 and 1941 625 foot towers *and* perhaps one of the 1931 towers still standing? Emergency backup perhaps??


    For the non engineers AM tower wavelength has two meanings, electrical and physical.

    When Andy refers to the electrical length that is not the same thing as the physical height.

    Capacitance and/or inductance can be manipulated in a tower circuit to “electrically” make up for a lack of physical height.

    This way a tower which is physically 4/10 wavelength can be tuned to appear electrically as a half or 5/8 wave.

    Electrical wavelength is commonly referred to in mathematic terms using degrees. a half wave would be 180°… a full wave would be expressed as 360°

    Simply using the frequency and tower height only tells you the physical length/height.

    Andy Brown

    The backside of that is that the more loading you use to (increase) the electrical wavelength for a physically short tower, the more power is lost in those components and less is actually radiated. If the mechanical (physical) wavelength is less than one quarter wavelength, even with loading you are significantly compromised.

    For example, 860 uses towers more suited for 1550 and are less than 1/4 wave @ 860 and come up electrically short at 81º Both mechanically (physically) and electrically they come in at approx. 23º or less than a quarter wavelength. Close, but clearly a compromise. Clearly any top loading would effect the 1550 signal so it’s probably not loaded much (if at all) and if it is it’s not doing much.

    I don’t know to what extent you can increase the electrical wavelength (of one of multiple frequencies) when you are diplexing AM transmitters.

    Fortunately for 620, a half wave @ 1190 is greater than a quarter wave @ 620.and the old Westinghouse towers have a physical height in excess of a 1/2 wave @1190 by about 10 meters. So KPOJ is not nearly as compromised as KPAM.

    Propagation is always superior in a tower that is physically longer then one that is made to be longer through loading.


    Maybe, I’m way off on this but if you lose more power with more loading, wouldn’t running more power obviate the need for the loading? Is it just not done because of power restrictions or would it cause more interference anyway? I may not be clear on this. Let me know if you need further explanation.

    Andy Brown

    You can’t “run more power” because that amount is licensed and fixed. You are allowed a fixed amount for losses, and loading just adds more losses.The power to the tower must be the licensed amount, and adding loading just means less of that power radiates and is lost in the loading. You also have to be careful because you reduce bandwidth.

    It’s pretty complicated. You can add about 30º of length, but it is fraught with side effects.

    Mostly top loading is used, very rarely bottom loading. Remember, the entire hunk of metal

    is part of a tuned circuit and tuned circuits are a bitch. Trust me. Add diplexing and it just

    gets more complicated.

    Think of it this way, if you weld a chunk of metal onto any radiating antenna, do you think that chunk of metal is going to radiate as efficiently as the more properly designed part of the structure? Keep that in mind and wade through some of this:

    Broadbanded AM antennas

    Remember adding inductance in series raises impedance and at a fixed power that means less current. It’s not that simple, but you get the idea.


    Thank you, Andy.

    Andy Brown

    23%, not 23º (typo on my part up two of my posts).

    You’re welcome, semoochie.

    Here’s two other documents I want to read, but haven’t yet.


    AM Radio. KPAM 860. Doing operation Santa Clause. Helping veterans and their families. Check out Bob Miller. Noon to 3 this week.Like old time radio again. If only for 3 days.


    Has anyone else noticed the terrible audio quality on 1190/620?

    Both stations sound like an old school 12kbps modem trying to pass something resembling audio.

    The NFL game on 620 Sunday sounded so bad that the announcers were drowned out by the swirling artifacts of the crowd noise.

    I then flipped around the dial, found 1190 sounded the same… and then noticed that the Seahawks sounded great on 1080.

    The death of AM will be hastened with audio like this.

Viewing 15 posts - 61 through 75 (of 91 total)
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