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Author Topic: 630 meters  (Read 40297 times)
K0OD
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Posts: 2557




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« Reply #30 on: September 26, 2012, 01:40:21 PM »

I'm enjoying this thread, Bunky

While you're waiting for authorization to transmit, you might listen to the range under 200 KHz. Several European longwave AM broadcast stations can be heard there most winter nights before EU sunrise. BBC is on 198 in English and there are a few French ones in the 162 to 183 range. Those stations run enormous power and huge antennas. I can hear them even in Missouri using my TS-850 and ham vertical. Nothing special.   
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GW3OQK
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Posts: 145




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« Reply #31 on: September 30, 2012, 08:30:05 AM »

Does anyone know how we are to MEASURE our EIRP in the real world?

To determine radiation on 405-512 kHz band when I was at sea we used Metre-Amps. Ships were given the value they had to achieve, example 102 metre amps. (Ant 30 metres height, antenna current 3 Amps, = 90 metre amps, not good enough.) The only article I see about this is http://87.194.135.226/ivarc/articles.php?article_id=69

Could this concept be translated into (knowing our antenna dimensions) the max current we should put into the base of our wire. Perhaps some of our maths experts could help.

I have my 1943 T1154 putting putting 18w into 50 ohms, so next step is an ATU for my inverted L, 13m high, 42 metre top, but maybe its not good enough. Certainy EU to USA will be a challenge.

Andrew
GW3OQK
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G3RZP
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« Reply #32 on: October 01, 2012, 01:11:14 AM »

I suspect you might find the info in the 1938 Admiralty handbook. You might need to calculate it by a roundabout route, though.

The use of e.i.r.p. is a bit peculiar - most standards use e.r.p below 1GHz, and the difference is 2.16dB.
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K4EJQ
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Posts: 101




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« Reply #33 on: October 21, 2012, 08:03:55 PM »

Hello from the "basement"- Now have FOUR-6146 tubes in parallel in the PA of the old WRL Globe Scout model 65 transmitter. 150 watts out on 475 KCS. Harmonics down -60 dbc. Had to give up using the planned little solid state exciter due to failing eyesight- Sooo...used a couple of 6V6 tubes for the oscillator and driver stages -I had the sockets already in place in the Scout. This ain't your fathers' Globe Scout anymore!!!! HI. CU on the band-WHENEVER
Bunky( in the basement)
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GW3OQK
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Posts: 145




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« Reply #34 on: October 22, 2012, 03:53:35 AM »

What's your antenna Bunky? ( Radiation resistance and reactance?) I'm looking forward to reading about your ATU and how you work out you are radiating 1 watt EIRP. I am about to make my own ATU. My antenna's an inv L, 0.4 ohms -j 1000.
73
Andrew
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K4EJQ
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Posts: 101




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« Reply #35 on: October 22, 2012, 10:23:37 AM »

Hello Andrew; I don't know what the rad. resistance or reactance of my antenna is. I hate to admit it, I have the bridge /oscillator and null indicator handy that I used for years making AM BC stn antenna resistance measurements with, but I just never got it hooked up on my ham stuff.
Let me briefly describe the antenna-nothing really special. Overall length is 165 feet. It's an "L" affair.  It is 55 feet in the vertical and 110 feet horizontal. Many, many radials-- some 165 feet long at the base. Antenna is used on all hf bands with a homebrewed -remotely controlled antenna tuner at it's base. I run QRO through it with no problems. This antenna is an outgrowth of several that I built back years ago and were described in some detail in a multi-part article I did for CQ magazine titled " The  Aerial Here is...".
On 630 meters I switch, remotely, appox. 540 uhy of inductance in series with the "L". This allows me to tune  the antenna  from about 400 to 560 KCS with good results . Using not -so- local AM BC stns and NDB's as reference signals. On TX on 475 Kcs , when no one is listening, HI, the SWR is less than 1.5 to 1 as indicated on a Bird Model 43 directional wattmeter USING A STANDARD 2-30 Mhz slug-which I don't know if it's all that accurate at 475 Kcs. I measure my TX power output on a 50 ohm dummy load with a 0-2 amp. RF ammeter in series with it. Several different meters were used from time to time and they all agreed as to a reading of 1.75 amperes using this load. Nothing "magical" about my aerial.
As for antenna efficiency-I have NO idea. Anyway, good luck with your project Andrew.  73,Bunky, K4EJQ
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GW3OQK
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« Reply #36 on: October 23, 2012, 04:03:07 AM »

Hello Bunky
I like to test theory with practice. This is the exercise I have done for my own ant, and I'll make an equiv dummy load for my atu and see if it works. EIRP is an imaginary power so I here's my imagination at work.

My reckoning from eznec is your aerial is R 0.8 , -j1100. To match it to 50 ohms use series L 400 uH, parallel C 0.055 uF. (You use more L but dont mention C)

Gain of ant 3 dbi, So for 1w EIRP, ERP = 0.5w.
With R 0.8 ohms, P = 0.5w I = 0.8 amps antenna current.

So, tune up and adjust power for .8A up the wire on your RF ammeter.

What do you think?
Andrew
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K4EJQ
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Posts: 101




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« Reply #37 on: October 23, 2012, 01:34:05 PM »

Andrew; Thanks for the note regarding the figures for the 1 watt EIRP operation on 630 meters. I forgot to mention in my previous post that I have 100 PF shunted across the antenna to ground to obtain best SWR at 475 Kcs. Again those figures are 540 uhy inductance in series with the 160 meter "L" (165 ft total length) with a 100 pf xmitting capacitor shunting the antenna to ground. The SWR is fine tuned with the motorized series capacitor in the remotely operated tuner at base of antenna. There are nearly 100 radials under the antenna varying in length from 33 to 165 feet-most buried but some lying atop the soil in the wooded portions of my yard. The QTH is atop a ridge line about 250 feet above average terrain. Ground conductivity is poor- yellow shale (soft).
One of these days I need to hook up the bridge and actually measure the antenna's rad. resistance and reactance. I am planning on running the full 5 watts EIRP that's permissible over here. That's why I added so many 6146 tubes to the final amplifier, HI. Even with 150 watts output capability I may still find myself short if the efficiency of my antenna is poor. I'm still trying to determine that.
Have fun and stay in touch. 73, Bunky ( in the basement)
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GW3OQK
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« Reply #38 on: October 24, 2012, 03:11:09 AM »

Hello Bunky, OK, if you have 100pf extra then you need more L to tune it out. I would put extra cap across the coax, not the antenna. For 5w eirp 1.8A into the wire antenna should do the job. (Do you have rf ammeter in series with the antenna, I mean RC dummy load, rather than in the coax?)

If anyone cares to calculate new figures it would be interesting. As far as I can see we can only use theory backed by the practical measurement to try and achieve the imaginary 5w eirp from the antenna by putting the right current into it. Hope I am right.

I have a Bird 43 2-30 MHz element too, and am interested in its indication at MF. I think it is reading low and could check by measuring the rf volts into 50 ohm load.

73
Andrew

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K4EJQ
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Posts: 101




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« Reply #39 on: October 24, 2012, 01:01:56 PM »

Andrew; Thanks for the follow-up. I must say you are really close with your figures on antenna current at base of the wire. I'm seeing from 1.8 to 1.9 Amperes (RF) at the base of the "L" with the tx putting out 140-150 watts into the 100 ft RG-213 xmsn line. The measurements with the RF ammeter were made at the output of the TX feeding a dummy load.There I see 1.72 amperes into the 51 ohm dummy load.

In fact I took my 0-3 RF ammeter out to the base last night to make the measurement as my curiosity got the better of me. After getting the readings I then fell down spraining my left foot. I'm a widower and live alone with my 7 cats.  ( Some would say that with seven cats you are not alone !!!) I'm down in the yard-- it's near midnight and even the cats have gone to bed Hi. I dragged myself back inside and went to bed after a stiff shot of "snake bite" remedy. I had had all the ham radio I needed for the evening. I took a second swig of the remedy and went lights out.

Just wanted to let you know your figures are "in the ballpark". I think it's time for another round of medication. Have fun ! 73, Bunky ( In the Basement )
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GW3OQK
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« Reply #40 on: October 25, 2012, 01:32:10 AM »

Well done Bunky, hope the medication reached your foot ok.

145 watts into the coax, about 2.5 watts radiated! Where has all the power gone?  Is anything getting hot there?

But please keep your fingers away when key's down. I have a cable from my tuner hut to the shack so I can key the tx from there. It also is used for the icom hf atu.

It makes me think my 25 watts MF T1154 is not going to be good enough and I need to make my antenna bigger with a very low loss ATU. Bunky, home brew of all kinds and experimentation is the joy of our hobby to me.
73
Andrew
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K4EJQ
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Posts: 101




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« Reply #41 on: October 31, 2012, 06:33:17 PM »

Hello again from the basement: Now that "Sandy" has exited the scene and the noise levels are returning to "normal" wintertime I am beginning to copy some weak signals from stations I haven't heard in the past. Does anyone have a list of CURRENT FCC issued EXPERINENTAL calls for the 630 meter operators other than the WD2XSH Group? So far , I haven't pulled in anything from across the pond. I am listening about each evening from 2300-0300Z-static crashes permitting. 73, Bunky ( In the basement)
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K0OD
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« Reply #42 on: October 31, 2012, 10:31:40 PM »

So far this season, signals from European AM broadcasters in the 150-200 KHz range have been way down from last winter. Perhaps it's too early in the season. Wasn't even hearing many NDBs last night.

However right now (0500z) tons of NDBs are strong. The AM broadcasters are just weak carriers here in Missouri. The French powerhouse station on 162 is just barely detectable.   
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K4EJQ
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Posts: 101




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« Reply #43 on: November 06, 2012, 11:08:46 AM »

Andrew et al;

Again, curiosity got the better of me. Last weekend while enjoying a brief bit of "Indian summer" I hooked up the old General Radio Bridge/oscillator unit and measured the feed point impedance of the 160 meter inverted "L" system I use on all bands 475 Kcs through 30 Mhz with remote tuner.

With the tuner disconnected and the bridge connected between the feedpoint and ground system measured the impedance at 475 Kcs at 40 Ohms with appox. 2800 Ohm Cap. Reactance. A second , almost identical inverted "L" that uses the same ground system and runs at right angles to the first "L" was measured at 35 Ohms with 2000 Ohms Cap. Reactance.

A quick check of the system at 1840 Kcs showed "L-First" to be 70 Ohms/400 Ohms Ind. Reactance and "L-Second" to be 68 Ohms/375 Ohms Ind. Reactance.

I then took the bridge/ oscillator unit to a friends QTH that also is planning to work 475 Kcs. He also uses an inverted "L" antenna antenna but not as an "elaborate" ground system as the one I use. His measured 20 Ohms @ 1000 Ohms Xc at 475 Kcs. To double check myself on the measurements I had a fellow ham who is technically inclined to duplicate the measurements made. We both came up with pretty much the same readings.

RF ammeter readings at the base of my antenna while on 475 Kcs show about 1.65 amps of current with the TX delivering  130 watts to the input of the remote tuner. Nothing is getting "Hot" as far as I can tell. I must admit I am pleasantly surprised at the overall "apparent" efficiency of the system at 475 KCs.

I have used these inverted "L" antennas for close to 18 years now on all bands and have had good success with them , both receiving and transmitting.

Good Luck with your planned 475 Kc operation OM.

73, Bunky ( In the basement)

PS: The foot , sprained a few days ago, is getting better with the imbibing of copious amounts of ""snake bite" elixir , HI.
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ZL1BBW
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Posts: 373




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« Reply #44 on: November 06, 2012, 02:31:10 PM »

How I wish I had kept an old Oceanspan :-)
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
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