AM Phone in Canada on 75-80 meters?

[VE3GZB]

I know it's been a while since I posted....things get too busy for me.

I've redone my transmitter completely and I'm trying to make contacts on the air. So far it seems I'm receiving nothing but commercial SW broadcasts and SSB Ham conversations in my area (Grand Valley, Ontario, Canada), and any/all of my attempts to contact anyone via AM Phone are ignored.

Is AM Phone dead?

I know that my antenna can put out some kind of signal....my friend VE3AWA who lives about 150 km south of me, he received my then-unmodulated test carrier, putting out 1.6 Watts into a Zepp antenna 60 feet long. He received me at an S9 level.

My new transmitter is capable of more than double the output of the previous design. Yet I find I am making no contacts. It's very discouraging.

I'm going to try again tonight, in the 40 meter band first, then switch to 80 meters in hopes of making some contact. So far 80 meters seems totally polluted with SSB and commercial broadcasts.

73s
geo
VE3GZB

[Tom WA3KLR]

Usually on weekdays there was a group on after work on 3725 kHz with Al VE3AJM the strongest here is eastern Pennsylvania.  I haven't listened to them lately.

By the way, a topic like this should be posted in the QSO section.  Hope to work you on the air soon.

[WB2YGF]

I dunno, 3W is pretty tough sledding on 75.  

[VE3GZB]

BTW, the modulator just happens to be related to something I just stumbled upon in this forum....I'm using a 6AS7 in series with the PA for AM Phone, something I thought of here at home.

1/2 of the 6AS7 is for a fixed 150 volt output to run the screen grid and master osc.  I'm keying the 150 volt output when I key the mic.

The other 1/2 of the 6AS7 is driven by a pair of cascaded 6AU6's for mid audio frequency gain. Output from the modulating half of the 6AS7 gives over 100 Vp-p to any succeeding load equal to or greater than 3500 Ohms (I tested it down to 1000 Ohm 20 Watts and the 6AS7 didn't fail, the plate just got red hot).

To adjust for load draw, I put variable pots for 150 V and 200 V voltages so I can trim it. There's no feedback in the power supply, it's open-loop and the 6AS7 has a low enough plate resistance to manage it well.

Reference voltage comes from a 150 V glow tube which I'm also using to drive the oscillator and screen grid of the PA Pentode directly. To keep the minimum current alive under load through the glow tube, a set of relay contacts key in some extra parallel shunt resistance to provide greater current to the glow tube when the mic key is pressed in, and takes the resistance out when the mic key is up.

The Transmitter itself consists of a power Triode (Cossor 215P) in Hartley, directly driving a power Pentode (Cossor 220PT), driving a Pi-antenna tuner. The glowing lamp indicates current flow in the transmission line (450 Ohm twinlead).

The Cossor 220PT loads up to a maximum of 45-50mA and though it's rated to 150V on the plate max, I found it will work just fine up to 200V on the plate with 150V on the screen.

The Master oscillator can be switched from 40 to 80 meters, and from VFO to Xtal mode (not yet 100% perfect but very close).

[ka3zlr]

Excellent Build, well done OM....FB piece of inspiration there.

TNX Fer Sharing it.

73
Jack.

[VE3GZB]

Thanks. Eventually I'll draw up the schematic and post it here for both the Modulator/PSU and for the Transmitter.

Now if only I started making contacts!

[Sam KS2AM]

I'm going to try again tonight, in the 40 meter band first, then switch to 80 meters in hopes of making some contact. So far 80 meters seems totally polluted with SSB and commercial broadcasts.


Now if only I started making contacts!

Hello George,

I think it's going to be pretty difficult to notice a 3 or 4 watt station calling CQ on 75/40 meters.

Can you give us a specific time and frequency that you will try so that we can listen for you ?


I'd suggest picking a frequency in the relatively quiet areas between 3600-3700 kc or 7125-7200 kc sometime during the evening and announcing it here first.



Sam / KS2AM

[VE3GZB]

I know my rig has better frequency stability on 80 meters than on 40 meters (also because all of my Xtals are for 80 meters), but 40 meters seems to be much quieter too.

Unless I post otherwise, I'll try tonight between 8 to 9 pm (Toronto time), I don't know which frequency I'll try yet because I'll have to search for a quiet spot on either 40 or 80 meters.

I'll search and post here tonight before I go on the air.

73s
geo
VE3GZB

[Ed-VA3ES]

Most Canadian AM activity occurs around 3725 or so, typically from about 4:30 PM ET  to about 6:00 PM ET.   Other times at random.  Occasionally a few guys go up to the "ghetto" at  3880/3885.

What kind of antenna are you using?   3W  is kind of weak for 80M, unless you have a full-sized dipole up at 50 feet or higher.   If you're  up on 40, try 7160, or 7290/7295.

[K1JJ]

Geo,

That's a pretty cool looking breadboard style layout.  It's fun to see the rig laid out like that when operating. 

You could always add some Plexiglas later on as protection as you get acclimated and lax with the rig...


BTW, 3 watts is really not that weak of a power level when it's put in perspective.   If someone is in good cornditions, they will often be S9 + 50db over when running a 300 watt carrier. You are only 20 db below that power level - or would be 30db over S9 using 3 watts - assuming the same location and antenna.  Using Your 60' long Zepp on 75M will reduce the signal level somewhat, so keep that in mind. Should be par on 40M though.

As Ed said, the key on 75M will be to use a  1/2 wave dipole at ~50'+ high, positioned flat and of low loss.  There's many guys on running AM riceboxes at 10 watts holding court. However at night, the competition gets big from ssb, static and general noise, so more power is needed just to keep a relative position in the mix.

I've found the best time for 75M PW activity is usually between 3PM to sunset during most of the year. This is a window for activity and propagation.

I have many times called CQ using my 2 watt PW rig and had several responses here in New England. I use a simple 60' high coax fed dipole for local work on 75M.  PW contacts up to 300-500 miles will be the limit most of the time on 75M, unless condix are exceptional.


Good luck.

Tom, K1JJ

[VE3GZB]

Thanks, I'll look into what times of day might work best. Will be too busy today with other family stuff, getting my car fixed, etc...to have time to play but I'll have more time on Sunday.

Here's a drawing of what my layout looks like.....minus the proposed tuned autotransformer idea I have drawn (but not yet tried so my antenna is just about 60 feet of wire attached to the transmission line).

What do you think? If I attached a tuned autotransformer to my Zepp to try and match it's apparently high impedance to the 450 Ohm transmission line, would there be any merit? Has anyone tried something like this?

My wife won't hear of me stringing ugly transmission line into the middle of the backyard, she's worked so hard to make it nice looking and she doesn't want the middle of the yard looking like some lab experiment, so my layout has to remain with the transmission line near the house (it's about 1 foot from the TV tower, held in place with a plastic coathanger and tape).

[ve6pg]

..i'm not far from you, as i'm just south of hanover...3725 has been the canadian watering hole, fer about 15 yrs, anyway...even with your low power, i'm sure i'll hear you....check in the mornings, on weekends, at about 8:30am on....

..tim..

..sk..

[k4kyv]

What is the purpose of the tuned autoformer?  Wouldn't it be better to have the matching network at the transmitter end of the feed line?

If the zepp is cut close to resonance on 75/80m, and you have 60' of feedline, the end of the transmission line should appear as a low impedance with little or no reactance, depending on the exact length of the feeders and  flat top.  You might be able to feed it directly from the transmitter with no matching circuitry at all, particularly if the transmitter uses link coupled output, although a balanced tuner in series-tuned configuration would be be more flexible, allowing you to QSY across the entire band, and would preferred if the transmitter uses pi-network output.

If the transmitter has a link coupled output, it is possible to cut the tuned feedline slightly too short, so that the capacitive reactance seen by the transmitter exactly resonates with the link at the operating frequency.  This eliminates the need for a tuner and its inherent losses.  The disadvantage is that you are pretty much stuck close to one spot in the band.

Another trick is to use a rotary inductor in series with one side of the feedline and trim the length of the feeders so that it resonates at the high end of the band with only two or three turns of the rotary inductor in use, and as you QSY down the band, it can be resonated by rolling in more turns on the inductor.  Years ago I ran a full kilowatt on AM using that configuration, and the rotary inductor, one taken from a 6-9 mHz ARC-5 command transmitter, didn't appear to heat up at all, although I had to keep the roller contact perfectly clean to avoid sparking.  The losses in a simple rotary inductor should be much lower than those of a full-fledged L-C matching network.  However, the worst-case losses in any well-designed matching network should be no more than about 10%, which would make no perceptible difference in signal strength at the other end.

There will always be some feedline unbalance with the end-fed zepp antenna, inherently due to its design.  Minimum unbalance occurs at the self-resonant frequency of the horizontal flat-top.  At extreme ends of the band, far away from the resonant point, the unbalance may be considerable, but if the antenna can be made to take a load from the transmitter while keeping the transmitter plate tuning in resonance, this usually doesn't hurt anything.  The antenna will just act slightly like an inverted-L instead of a purely horizontal radiator, but most of the radiation will still be from the flat-top portion.

[VE3GZB]

The total length of the feedline (I'm approximating here) is about 45-55 feet, including the length coming in the house down to my gear.

My transmitter is using a Pi network to couple the feedline to the plate. But the feedline is 450 Ohms and I've been told the Zepp may be anywhere from 2000 to 5000 Ohms, this is why I thought maybe it would make better efficiency to add a tuned autotransformer between the feedline and the antenna.

Adding further matching at the transmitter end of the feedline wouldn't correct any mismatch up in the air, it would only help "mask" the VSWR from the transmitter - any mismatch would still be happening up in the air.

I haven't tried this yet, so I'm just tossing the question out there.

My previous link-coupled transmitter design (I used my scope to measure P-P voltage across a dummy load, then converted the measurements to RMS) would deliver a maximum 1.6 watts. With my current antenna configuration (as drawn MINUS the tuned autotransformer) my friend VE3AWA reported S9 carrier levels when I link-coupled that transmitter to the same Zepp antenna.

So naturally I wonder if there is any further improvement possible in radiated energy by optimizing linkage from transmission line to antenna.

I use a series-switched-in CM1866 6.3V/0.25A series lightbulb to tell when output energy is maximized to the feedline. Then I can switch-out the lightbulb and link directly to the feedline. When I have tuned-up and load up the transmitter to what I think is maximum output, I'm able to make the bulb glow bright Yellow.

I'm probably not going to get any time on the air tonight - today was just too insanely busy for me and I've only just come home a few minutes ago (it's after 9 pm now)!

[ve6pg]

..what freqs have you tried?...do you have a vfo fer that transmitter?...

..sk..

[VE3GZB]

Yes, I have switchable VFO and Xtal capacity.

I can flip a switch to run the VFO to fully cover either 80 or 40 meters. I only have 80 meter Xtals on hand though.

I have an external frequency counter sitting nearby with a small dummy antenna to pick up radiated RF from the transmitter. I use the frequency counter to tune the VFO.

[k4kyv]

The total length of the feedline (I'm approximating here) is about 45-55 feet, including the length coming in the house down to my gear.

My transmitter is using a Pi network to couple the feedline to the plate. But the feedline is 450 Ohms and I've been told the Zepp may be anywhere from 2000 to 5000 Ohms, this is why I thought maybe it would make better efficiency to add a tuned autotransformer between the feedline and the antenna.

Adding further matching at the transmitter end of the feedline wouldn't correct any mismatch up in the air, it would only help "mask" the VSWR from the transmitter - any mismatch would still be happening up in the air.

With the classic end-fed zepp, the 450Ω line is acting as a tuned feedline.  Your length would be a little less than a quarter wavelength.  By definition, there is a mismatch between antenna and feedline, and it runs at a high SWR.  A tuned feedline should be able to run at 10:1 SWR or more with little feedline loss, especially if it is open wire construction or ribbon line with "windows" cut out.  I have even seen hams use solid 300Ω TV ribbon as tuned feedline with good success.  Of course, the best choice would be real air dielectric open wire line made of single-conductor wires separated by a plastic or ceramic spacer every foot or so.

The matching unit down at the transmitter end would tune out any reactance at the feed point and match the impedance seen at that point to the output impedance of the transmitter.  You would consider the quarter-wave resonant feedline as part of the matching system between transmitter and antenna.  At the antenna end it will appear as a very high impedance, but a quarter-wave down the line, at the transmitter end, it will appear as a low impedance.  Since your length is a little shy of a quarter wavelength, there will be some capacitive reactance thrown in as a component of the load impedance.

Before the advent of coax line, open wire tuned feeders were probably the most widely used feed system for amateur antennas.  Because of the high density solid or foam dielectric of regular coax cable, the feedline loss using even a perfectly matched coax line is little or no better than that of an open wire tuned feeder running at something like a 10:1 VSWR.  The main disadvantage of open wire line is the mechanical inconvenience of bringing it from the antenna, through the wall, into the shack to the transmitter.

Of course, the 450Ω open wire or ribbon line can be run flat, at 1:1 SWR, but in the case of your proposed system, any slight improvement in feedline loss due to the perfect match would not make up for the additional loss caused by the matching unit inserted at the antenna end of the feedline.  Plus it would be very difficult if not impossible to adjust the remote matching unit on order to QSY, and you would still need some kind of matching unit at the transmitter end of the feedline to match the output impedance of the pi-network to the balanced 450Ω load.

[VE3GZB]

Hmmm....fair enough.....still I'm frustrated that I'm not making any contacts.

I got up early enough this morning - my stepson gets up to deliver papers and his noise, plus the sun, woke me - and just after 8am I caught some AM activity on 3.880 (called itself DX60 net). Seems most of the contacts were a few hundred miles south of me, over in the US.

I could hear them - but they couldn't hear me. The only thing I heard comments about were "heterodynes". Were they hearing my carrier? I was speaking into the mike, I could even hear my own voice in my receiver (I keep the volume down very low to avoid feedback).

I even did a last minute patch into my modulator, hooked up my Heathkit power supply for extra filtered DC input to the modulator. Nothing.

I tuned up and down the dial, looking for anything or anyone else. I only found more commercial/religious broadcasters and others on SSB.

I'll try again later this afternoon, time permitting.

[ve6pg]

..roy, k8vwx, and craig,ve3cl  were on, this morning, on 3690....i just finished with bill, ve3cfy...on 3725..( 9:45)....try to keep away from 3880/85..too busy...tune down the band and look around 3690-3725....

..sk..

[VE3GZB]

I found AM activity at 3725 and at 3880. Everything else was either commercial broadcasts (foreign and religious), background noise and SSB which sounds like Donald Duck on my receiver (BFO is shot, the receiver is heavily hacked by someone before me and I don't know what damages previous owners caused).

I tried working both 3725 and 3880 and received no success at all. This is extremely frustrating.

[K1JJ]

Hmmm....fair enough.....still I'm frustrated that I'm not making any contacts.

Geo,

Do you have or can borrow a scope to be sure you are getting near 100% modulation?  Even though you hear yourself in a receiver, be sure the modulation level is high with that 3 watt carrier.   If no scope, then a PEAK reading wattmeter will show about 4 times the carrier on peak modulation when hiting near 100%.

Also, try a few contacts on CW. That shud tell the story.


Can you put up a 75 dipole with two legs running off the tower feedline instead of the existing end fed setup?  Even if the legs are inverted vees in both the horiz and vert plane, it shud do better than the 1/4 wavelength you have now on 75M. ie, Even two legs hung off the tower running out like a vee with the legs separated as far apart as possible may work reasonably well. However, if the legs are TOO close together, they will start to cancel the signal.  If you can pull it off, then we can discuss the many ways to feed it effectively.


The guys on AM shud be hearing you at 3 watts, especially with a large group in a net with widely varying locations.  Check out the possibilities I mentioned above and report back again.

T

[ve6pg]

..geo...i'll try again, sunday afternoon, about 4:30-on ward...3725...
..btw, you should not be hearing anything on 75m, except hams...there are no broadcast stations, on the band...sounds like your receiver needs an alignment, somehow your receiver is being overloaded....

..sk......

[VE3GZB]

Yea, I don't have 100% faith in my receiver, I'm using my transmitter and frequency counter to make sure my receiver (beat up Hammarlund HQ-100, it's been hacked by someone else as I mentioned earlier) are tuned to the same frequency. I listen in while I tune up at reduced volume and look for my own signal, just to make sure.

The receiver has a number of spurious responses, especially when it's expected to run right next to a transmitter. But tuning while not precise seems to be ballpark accurate at this writing.

I can't change my antenna, my wife worked so hard on making the backyard nice and she won't hear of me stringing up ugly feedline in the centre of the yard. I have to make things work as they are.

I did some tests here...yes I have a nice 100MHz scope and I'm using series modulation (6AS7 in series with the plate of the final) and I'm able to modulate up to and even beyond 100%. The plate signal to the final can swing +/- 120 Vp-p on top of 200 VDC to the plate so I have to monitor how I speak so I don't overmodulate. And a 6AS7 can pass a respectable amount of current so there is no lack of beef in this modulator.

I asked them at the farm, about 5 miles from here, to see if they can tune in my signal on their shortwave. I instructed them to tune in just above 3.7 (I'm tuned to 3.72) on their shortwave receiver.....I could hear the receiver as they listened and they couldn't find my signal. They tuned up and down and it was just noise and static.

Then I tried something drastic. Just to see what would happen, I patched-in a newer, much stronger tube - a 6BQ6. Took me about 20 minutes to patch it in.

It all tunes up and behaves normally, the series 6.3V 0.25A lamp glows so brightly upon tuneup that it literally leaves spots before my eyes even as I type this. Then I switched out the lamp, I called them at the farm to try to pickup my signal again - no luck!

Maybe their receiver is on the wrong SW band? Possible since they don't use it regularly.

I don't believe I'm putting out no signal. Not after all of this, no way! I'll try again later and hope!

[K1JJ]

I can't change my antenna, my wife worked so hard on making the backyard nice and she won't hear of me stringing up ugly feedline in the centre of the yard. I have to make things work as they are.

Geo,

Sounds like your modulation % is OK - good.

Reread my last post about the antenna. You don't need to run the feedline out to the middle of the yard, though it would be nice.  Feed it in the same place as now, but run TWO legs out spaced as far apart as possible. This will give you a balanced antenna and 1/2 wave on 75M.   All you will be adding to the XYL's picture is another thin wire.  There are many options of feeding it.

T

[VE3GZB]

I'm not sure I can quite picture what you're describing? Can you link to a jpeg or something on the internet to illustrate what you mean by "running two legs"?