Then I would try with a straight L-C or C-L antenna tuner first. Such an arrangement might not benefit from complex loading arrangements.
I've worked LF with capacitive hats and found the best efficiency to be in a base loading coil (or as found in ordinary tuners at HF). The cap-hat is what boosts atenna efficiency by increasing radiation resistance rather than the matching method.
I wanted to come back after the mods. on the ATU, which is now an L-C-L system, meaning the inductor is to be connected between ground & the junction of both var. caps.
The experiments so far have been somewhat positive (on & around the fq I use, 1593), with just a trial coil of around 30 turns of insulated, multifilar, 3 mm diam. wire on a 11 cm diam. form. I'm using nearly 10 m of this wire I bought for the new lead of this 45 m inv. L. Tomorrow, I intend to build a new coil with taps and then see what happens. The inductor will preferably place indoors, next to the ATU.
Weather permitting (it's been late Winter time like here), tomorrow too I hope to modify the inv. L lead which, among other wrong aspects, is constantly swinging because of strong wind.
I tried all this with a DRAKE MN-7 ATU used just for measuring the SWR & the power level which may surprise you as the tiny iTx hasn't enough power to allow any readings *at all* on this network, but I used something different just to "see" how the antenna+inductor were performing.
It's something that can theoretically tx down to a bit less than 1500, but on 1620 the max. power is already low, not more than just a bit less of 20 w. The signal, buy the way, is not AM, it's A3H,, not DSB/AM.
It's my personal experience that using a roller inductor in combination with a capacitor works best for easily tuning up a slightly shorter than 1/4 wave inverted L or vertical antenna. It takes some fine tuning of both the capacitor and roller inductor to find maximum current between the tuner and antenna but once it's reached it will act exactly like a regular loading coil with the added benefit of being easier to tune and better Z match. Also works nice if you use more than one frequency often. Pirate Cat radio gives a good example of this setup here... www.maxmcarter.com/classexmtr/circuitdescription_files/antenna.gif
Efficiency should be near or equivalent to a loading coil and will allow for large variances in aerial length and even potential ground soil conductivity changes during different seasons. If you have the space it's best to setup a full length 1/4 wave inverted L. For 1610kHz it would be around 145' of wire. Resonance is key of course and even with the full length of wire you still will have to snip off inches at a time until you find maximum current or maximum field strength. The rest of the antenna is in the ground (other 1/4 wave section). As many ground radials as you can stretch out and ground rods at the feed point and possibly ends of radials. Even one radial is extremely better than none, after all that is electrically half of your antenna!
The ground radials should be electrically close to 1/4 wave length. The idea is to act like 1/2 of a dipole in the dirt. Obviously this is not easy to do if you don't have the space and obstacles will get in the way, so just get as much wire down as possible and ground rods. Since that other half of the wave has to go somewhere, if it doesn't have a full 1/4 wave to look into as a ground then it will try to find a ground, which can end up being your audio cables, house wiring, and anything else that couples into your transmitters RF ground path. That can cause RF to flow back into equipment and cause hum and RFI. I would imagine that an UNUN could possibly solve that, but may be no more effective at it than simply using audio line isolation transformers or even audio line chokes. It all depends on the situation and what works best.
Technically you can use a 1/4 wave ground plane antenna w/o an UNUN on any frequency, and an inverted L on medium wave is still electrically equivalent (just bent at the top horizontally) so the rule still applies. If the radials are too short, or if you are getting excessive RF back into the shack an UNUN may be needed to choke out RF on the coax back into the rig, though it may not be a do all end all situation.
Think of it this way.. AM MW licensed stations don't use them when running full sized marconi antennas, so you shouldn't either. However there is always that chance it can help a situation where other means will not.
Contrary to what I expected on Friday, I was unable to modify the lead of this 45 m inv. L, but at least experimented a bit with coils with both the mini-tx (iTx) as well as the "other" tx, both via the modified ATU.
On the iTx, I removed the coil w/ taps that I had inside the tx plastic box and built a new, external coil with taps: 85 turns of 0.8 mm diam., insulated unifilar wire on a 9 cm diam. form. No ATU, just the inductor. Since my usual fq is 1593, I tested & tested... and it seems the best signal is achieved on the tap 7 (=70 turns), but, surprisingly or not (this iTx is too rustic) there's a fairly strong signal on the same fq on other taps too...
Then the "other" tx. As expected, tuning is a lot more critical, but at least the ATU works well despite being uncertain about the smaller var. capar. value, and the power level is higher of course. Fq wise, it's no surprise that the strongest signal is around 1690 because of the inv. L+lead dimensions, but I don't want this fq - too high for picking up the signal on either jeep radios.
A tapped coil is a poor, home made "roller inductor", but would like to use one instead.
Would you suggest a roller inductor w/ the value mentioned here www.elektrodump.nl/1662-Rolspoel.html for instance? Would appreciate a word from you on this.
Aerials. I know the inv. L is nothing but a variant of the traditional monopole, but either this current inv. L or a shorter inv. L, like 25 m hung somewhere else is all I can use for tx as I already have other [receiving] aerials around.
The lead cannot be longer than, what, some 8~10 m.
Would you suggest a roller inductor w/ the value mentioned here www.elektrodump.nl/1662-Rolspoel.html for instance? Would appreciate a word from you on this.
Something like that will work fine. If there isn't enough inductance you can always tie in another coil in series with it. At least then you could get the exact inductance you need rather than just a close approximation via a tapped type coil if using it by itself as a loading coil. I only mentioned that though if you can find one cheaply, otherwise a tapped coil will work just fine. You can even put a smaller coil inside of the large tapped coil that has its own axle and form what is called a variometer inductor like this... www.northcountryradio.com/Articles/variomtr.htm Probably a bit overkill but just figured I would pass on the idea.
If you don't have a field strength meter now would be a good time to get one or make a simple one. It will help you greatly peeking an aerial. Even placing a lightbulb (or ammeter/milliammeter) between the aerial and tuning unit and tuning up for maximum brightness, then shorting the bulb wires is a simple way to make sure you're pushing the most current you can into the air which is a quick and dirty way to make sure the antenna system is working well.
Thanks for coming back with the information & other tips.
Now that I mentioned .elektrodump.nl, some of their txs are about the same, if not the very same found in .pll.gr.
Unfortunately, some of the roller inductors depicted by the Dutch firm miss the value, e.g. www.elektrodump.nl/1659-Rolspoel.html, but I'll drop them a line as tapped coils are simply not as good & practical.
Txs from Northcountry R, Ramsey, SSTran & others like three models of 3, 10 or 25 w covering just 1350~1700 from R.Morningstar have been put into equation before deciding for (you guessed) the RFsource PLL exciter. The fact is, that ordering something from the USA (or from any non-EU countries) turns things complicated.
Having said that, of course, I read about variometers too, but haven't decided to build one. This 100 turn coil I have for iTx was made acc. to what I could read in Northcountry R.
As far as the iTx is concerned, the type of circuit is not allowing me to use this home made ATU after modifying it to work in an L-C-L arrangement. It's far better to use the inductor I built last year: 100 turns, tapped every 10 turns, over a 5 cm diam. form; I can send on *any* fq way up to at least 2 MHz. You know this tx, of course, so you know valves are a lot more forgiving in terms of mismatch. I'd like, however, to try another PA valve that might put a few more power w/o modifying the PSU ("battery eliminator") that I also bought.
The antenna. I said I couldn't have more than a 8~10 m long lead. Well, weather was a lot better today so I worked on the T2FD and also on the inv. L, and decided to hang it at the same height the upper tip of the T2FD is, 17 m above ground, and so I did it.
The 45 m inv. L lead is now reaching the garden, meanig it's abt. 17 m, but I decided to take it to the radio room and experiment with it.
Frankly, it was a bit of a disappointment! I was expecting a stronger signal on my rxs, but that is not the case. I also tried it with the "other" tx + the L-C-L ATU, and could see nothing marginal improvements as checked with SWR/power meter of the DRAKE MN-7 ATU (which was *not* used for tuning, it was used solely for measuring the signal). Maybe on account of now so good grounding but I have to work w/ what I have.
I suspect you'll now tell me to place the lead tip at ground level and put the ATU+inductor there, and then a 50 Ohm cable into the house. This is planned for the days to come.
Unfortunately, the longer lead I now have is not vertical, it slopes on a 25º angle, and is somewhat near one or the tower guy wires as well as a 450 Ohm ladder line for a 2x15 m, 60 m band inv. V.
Let's see how the next experiments go. Again, thank you for your help, Kage.
I wouldn't worry too much about getting the vertical part perfectly vertical, or the horizontal nice and horizontal. With inverted L antennas you can bend the rules a bit. You can slope the end of the horizontal part downwards if necessary, and the vertical part can be slanted. In fact the antenna I use is 100', 60 horizontally out to a tree and 40 vertically... but at a slant as the pole supporting the wire is only 28' at the moment. Actually it's probably more like 120' total as the lead in wire runs horizontally a few feet above ground into my room and is also hot with RF. Even with it sloped my signal at 10 watts easily covers 3-5 miles, and much further on a car radio or person who has an outdoor receive antenna.
I am not sure exactly how your transmitter works but if it has a loading coil built in I would bypass it. Just feed the outside tuner/antenna off of the final transistors output directly or after its filtering if there is some. If it's only a 100mw part 15 transmitter I wouldn't expect too much range. It takes at least three times that power to get out a few miles or more with solid power for most setups.
Anyways not to derail this thread but if you'd like go ahead and open a new thread for further questions. I will be happy to help out and am sure others would also. AM mediumwave is really fun to get on but takes some work and traditional methods of tuning up antennas for shortwave and higher frequencies really don't apply well to mediumwave. They really are different beasts. Most of the pirates I have talked to using mediumwave including one well heard in the US use rangemasters or procasters into a mosfet linear or some other kind of low band amp to get into the high powered ranks. Many have gone out into the woods and setup full sized dipoles and get out thousands of miles at night. Heck I am just happy with covering my town during the day via groundwave lol.
edit: one more thing.. Not sure if you have possibly made this same mistake I made early on but the tuner or loading coil has to go *directly* into the antenna/ground system. There can not be coax between the tuner/loading coil and the antenna itself. However you can run coax from the transmitter out to the tuning system. I'm not real clear how you have setup your transmitter, but I have seen others accidentally make this mistake.
Well, to start with, that 25º angle I mentioned, it's wider for the time being as you cabn see it on the attached drawing I prepared. I should have explained it a bit differently, I mean the angle *will be* 25º *after* I shorten this current 17 m long lead in and leave it closer to the house, in a way I can conveniently house an ATU, viz. under the edge of the 3 m high roof on the garden opposite to the house.
About feeding the iTx or the "other" tx directly w/ the 50 Ohm cable, no, that only exists between the home made L-C-L ATU or the DRAKE MN-7 and any of the other two txs, be it the "mystery" one or the iTx.
The "mystery" tx, possibly like others covering 160 m, can, as I said, send down to 1500 (even a bit lower than that), but you know better than me the circuitry was not designed for that, hence the vy. low power level it can reach at 1620, 10 w, and not a bit under 20 as I said the other day. Of course, the power level increases as one goes higher, like 1660 where think the SWR/pwr. meter of the DRAKE MN-7 can be properly adjusted prior to measuring.
Finally, the range of the iTX. After the Sunday's changes, I checked on the Land Rover 110 radio today, and could see the range did increase as I can still hear the signal well over a km away all depending on the blockage by buildings, so I can only imagine it can be picked up at a greater distance on a house rx w/ an ext. aerial, I mean rxs like those we DXers use.
As to the tx I am using, the "complex" iTX, I am also enclosing the schematics of it where you can see there's no transistor there, it's a valve unit albeit very simply constructed. BTW, the new inductor for it now consists of 19 turns of 1 mm diam., insulated, multifilar wire around (don't laugh) a used silicone rubber container which translates into a 5x22 cm cylinder shaped tube - and it works nicely 1400~1900, so fits the fqs I use.
Kage, if you feel a new Thread is more appropriate for discussions about aerials, please do open one.
I could be wrong but I think that 22uH coil in the schematic is there to load up the transmitter into a 10' antenna. Much like many of the other kit transmitters that are designed for part 15 operation they have a similar coil on the tube/transistors output so it easily loads up into a 10' legal length antenna.
Unless you are using an external linear amplifier or something you haven't mentioned (or I skipped over reading?) there is no way that transmitter puts out 10 watts. The maximum output that would have would be <100 milliwatts or 0.1 watt. If you want to drive a longer than 10' antenna off of it you will need to bypass that 22uH coil and possibly remove C8.
Sure, the iTx, exactly like similar others, are theoretically designed to use what I term as a miserable 3 m long piece of wire as an antenna. This is pathetic.
Of course, the so called Part 15 of the FCC doesn't apply elsewhere but in the US alone, so that is *no* concern whatsoever for us in Europe, and that's often why some valuable data on txs & antennae never consider longer pieces than the ones allowed to US users.
(I notice you don't use to refer to the metric system - I take it you're somewhere on the side of the Brit. Channel, , but not "across the pond" - true?)
As to an ext. amp., oh no, I am using nothing of the sort. The one & only amp. I have is that RFsource "pallet" that got damaged, and besides that the RFsource PLL exciter to drive the former. Until at least the latter is fixed, for it vy. much seems it's faulty, I only have the iTx and that "other", mystery tx I don't use for two main reasons: a) it sends on A3H, not DSB/AM, meaning audio quality is actually worse than that of the iTx, and b) it is not meant for prolonged operation just like most (if not all) amateur transceivers. At the least the dedicated, fan cooled PSU runs hot. The tx also has a fan by the way.
You mention 10 watt, but I never said the iTx puts such power level; perhaps you're confusing with the "other" tx. This one has the following specs.:
SSB/CW 250 w PEP, A-3H 80 w carrier + sideband (upper) Duty cycle 100% for those 3 modes Tune, SSTV, RTTY, w/o fan, 33%, 5 mins. tx max., w/ fan 100%.
Finally, again on the iTx, I shall try your suggestion of bypassing the L3 coil and possibly the C8, and see what happens aerial wise. Apart from this I don't know how power could be increased a little bit on the iTx: a different oscillator valve perhaps? But then I'm convinced the voltage might be diff. too.
Oh, one other thing I forgot to add after installing the new lead: in terms of audio quality, there was a slight improvement too. I am aware modulation quality varies acc. to the diam. of the radiating element, so this must at least one of the explanations.
Maybe this particular topic doesn't belong here, but I would nevertheless mention it as it is related to adjusting aerials.
I found a useful table entitled "Antenna Calculations from Panaxis for MW Antennas", but there's a parameter I don't quite understand which I'll explain later.
The question is this: is the "additional capacitance (hat, etc.)" parameter supposed to be be filled with the length of the top hat (in my case, a 45 m wire) or the capacitance of it?
If it's the latter that's correct, how we determine the value?
Needless to say the aim is to determine the inductor for a given QRG used with an aerial which in the case of yours truly is a 20 m lead into a 45 m wire, or in simple terms a 20+45 inv. L.
That's the only parameter where my doubts reside.
I'd highly appreciate if someone could provide any help. Thanks in advance.
Many days past since I posted my 9th inst. message and... "many, many replies arrived."
Not to worry, the capacitance issue was solved, and I'm now using the homemade C-L-C type ATU with something new instead of a mere inductor which is a variometer I decided to build, and if not fully correctly made, it is about enough for the present sitation.
Maybe someone could try 1675 evenings and find "something" out of ordinary in terms of the usual content in these matters, if a 30 watt signal is capable of some reach that is...
I have a question about a 1/4 wave GP antenna that is built according to this picture below. If I built it like that using 50 Ohm RG58\U Belden coax, do I still need to add a BALUN?
As far as I know (so, others more technically minded, pse. go ahead too!), there's no need for a transformer as the angle between the vertical element - the radiator - and the artificial ground plane - the "radials" - turns the impedance value to about the same as the 50 Ohm co-axial cable.
In theory, such an antena will work w/ just one "radial", but such a configuration is not adequate, so more are used, typically a minimum of about 3.