"I take from the experience a positive feeling, that I too could achieve a PLL driven transmitter."
The very reason why I posted those pictures is to show you that these transmitters can have PLL. This particular setup is operating in the lower 3rd of the band, which again demonstrates that your unit can operate with a PLL.
When I put this PLL into the AM 25 unit, I will post those pictures as well.
Remember, these solid state LPB AM transmitters all used the same A1 and A2 IC's as well as the same balanced modulators and audio IC.
Your unit's exciter can also be driven by a PLL circuit, either the Datakit with the added oscillator, or one as shown in the images which has an on-board oscillator.
Just wanted to help you toss aside any doubt about the PLL route for your unit.
RFB
I am signed on to the idea of going PLL, but the idea was originally suggested in regard to the Deep Voice long wave transmitter project and I still need a VCO circuit in order to make that work. I have already invested in a PLL Data Kit, so I am half ready.
For the LPB2-20 AM carrier current transmitter the PLL Kit and oscillator circuit are in hand, but the circuit arrived after I had ordered crystals for 570 and 670.
The 570 crystal still makes sense, but I may have erred with the 670, because the auto radio clearly hears 670 "The Score" from Chicago, WSCR 50kW unlimited from Chicago.
Another complication is that I would also like to try 970kHz, the clearest available channel, but the entire output filter of the transmitter would need to be re-built, so that may not happen.
If there was a contest over cost, the crystal would be more economical, except in cases where there is a lot of frequency changing.
The filter for the mid-band won't be that difficult to construct because the manual has the part values needed for each of the 3 sections of the band. If you take a look at that parts list for the 3 filters, you can see that the toroid cores for the low and mid sections of the band are not all that different. Varying by only a few uH from one to another.
Can't wait to hear the results of the two frequencies your going to try!
RFB
For several days I have been removing, one by one, the circuit cards from the LPB2-20 carrier current transmitter, for serious inspection. This has paid off big time because I found a cold solder and a bent pin on an IC that was turned under the chip and not inserted in its slot.
Also, the values of the 5 LP filter capacitors needed to be confirmed but couldn't be seen without removing the card from the case. Luckily, they were all correct.
This transmitter was built in 1981 and has gone through numerous lives under various owners, including a sex change from high band to low band.
Now it gets re-assembled but we need a correct RF cable to link it to the TCU-30 Coupling Unit for test on the power works.
"Now it gets re-assembled but we need a correct RF cable to link it to the TCU-30 Coupling Unit for test on the power works."
THESE are what I use to connect the
TX to the coupler.
RFB
Wow, thank you for that cable source. That is exactly the cable described in the LPB Manual. And it's blue!
you can use any 50 ohm cable between tuner and tx.
lmr400 is best. very low loss and high shielding
Yes kc8gpd, any 50-ohm cable, but the big trick is having a male UHF connector at both ends.
The manuals recommend RG-8 if the coax run will be long. At the MW frequencies RG-8 will do just fine.
Since it is most likely your TX will be sitting right next to the TCU, which is how my setup is, the linked source to the 3 foot long RG-8 coax will work perfectly, and is exactly the coax I am using at this very moment and there is no measurable loss at all.
It's real good coax and put together better than assembly line factory stuff. They are built by hand, by a ham radio operator and fully tested. You can get longer lengths from the vendor by request.
RFB
The 3-foot length seemed perfect, because the equipment will be in a single location and any extra length would need to be coiled up.
The LPB Manual says, "SO-239 UHF Type connectors, unbalanced, using 50-ohm coax cable. TYPE RG-8/U IS RECOMMENDED FOR SHORT RUNS (emphasis mine), Type RG-58/U is acceptable."
These blue hand-made cables fit the spec exactly.
"These blue hand-made cables fit the spec exactly."
That is why I posted the link to the exact cables I use. And yes they are exactly the type of cable specified in the manuals, again why I directed you to that vendor with the exact cable the LPB manuals calls for.
Besides...why attempt something different when the exact type you need is readily available at a great price, and hand built and tested by a real radio person!
RFB
My friend just sent me an E-mail.
It looks like I will have the
LPB RC-6A in my hands on Monday
or Tuesday, according to UPS.
My friend is still writing up his
report on the transmitter. This
guy is extremely thorough when he
has the time. He is very busy, so
I'm not sure what to expect.
But whatever he sends, it will be
useful.
As I mentioned before, my friend recommended
running DC on the tube filaments - that will
bring down most of the hum. I will eventually
try that. He also recapped the transmitter.
He said that was easy. I guess we're looking
at new tubes first. Another friend of mine
surprised me and ordered a crystal for 1020 kHz
from AF4K. A few problems came up. 1020 was
not in stock. Since I can't go below 1000 kHz
because the crystals are so expensive there, he
is now going to try to order a crystal for 1040,
which is empty during the day, and pretty clear
at night, too. There are two remaining questions.
First, will the transmitter tune up on 1040? There
is also a broken coil inside. The unit is working
pretty well on 860, where it has been for years.
(As you know, 860 is not a good channel here.)
But again, it may not tune up on 1040 because of
that broken coil. I told my local friend this, and
it seems he is going to order a 1040 crystal anyway.
We will see if a 1040 crystal is available, maybe it
will be, maybe it won't. The broken coil looks as if
part of it has broken off on the bottom. Some of
the "ferrite" is missing.
A lot more may have to be done with the RC-6A. An
oscillator may have to be built for a higher frequency-
to be divided down into the AM BCB.
All of this will take a great deal of time.
Carl, if you are out there, you beat me out on the
13.560 MHz rig, and it looks like you are going to
beat me out here with this CC thing, too. I say all
of this in jest of course. I am glad for you.
Anyway, I will keep reading this journal, and
I will let you know what happens here.
I see this as an antique radio restoration, just
like any other. So we will see where it goes.
Best Wishes To All
Bruce, Porch Light 2000(?)
That RC-6A can cover the entire band if the output tank is configured for it. The output tank is kin to the solid state unit's low pass filter, which is split into 3 sections of the band..low, mid and hi.
The RC-6A was built to specification of the customer's needs, just like the solid state units were.
If it was geared for the low band on the output tank, it will have a certain range it can cover on the lower third, same for mid range and hi range of the band.
I posted some time ago about my RC-6A unit that was damaged due to a drunk brother ramming his Camaro into the wall which was part of my room and the table where the RC-6A was sitting got knocked over and SMASH..there goes the transmitter...it was built to cover the entire MW band and had an output tank coil with an adjustable inductor coil to shift the tank across the whole MW band. LPB made these particular RC-6A's for sites that needed to change frequencies beyond one or more of the 3 sections of the band..ie from 700khz to 1400khz and so on.
Wish I could remember where that manual is. Sheesh that was many a moons ago!
But for your unit Bruce, a hunt for Red Inductor Core should begin now because either way, your going to need that second adjustable inductor to be working to cover the full range of the section of the band it is built for, otherwise it will be even more limited.
RFB
The hunt for red inductor core.
Very good!
Actually, I was watching "The Hunt For
Red October," just a few weeks ago.
I'll have the RC-6A in my hands today
or tomorrow. I can look at the coil
and see what the deal is.
My friend has yet to E-mail me his report
on the transmitter. But I have a feeling
because it's taking a while, it will be
a long report.
I remember your brother's (how do I put it,)
contact with your RC-6A. I know he got you
another transmitter. My memory says it was
the 25 watt version.
I feel badly for you - that you had to go
through that. It must have been traumatic
at the time. But again, you got a better
transmitter. So, I guess we'll leave it at
that.
Thanks for the info. I always enjoy it. I
was telling some tech friend that you may
be the most knowledgable CC person in the
country right now. That we know of, anyway.
There may be some other people, but they are
in the woodwork somewhere. We are lucky to
have you here. This is a subject that nobody
knew anything about until you came along.
Actually, KC8GPD knows a real lot of stuff. I
had forgotten about him, but he's way up there
in the carrier current world, too.
How much I don't know, but his knowledge is very
great, also.
Well, let's see what happens, and I'm really
looking forward to Carl's experience.
Bruce, Radio Dumpster 909
P.S. I've been coming up with all of these
weird Part 15 station names to goof on Carl.
I wonder what he thinks of this one?
It all started back in 73 when a big box arrived that weighed considerably, containing two devices..the RC-6A and a TC-8 coupler. Previous CC operations used a home built 10 watt AM rig and a home made line coupler using LC circuits.
Much of the self training came from reading a bunch of ARRL handbooks including the infamous issue I still have dated 1945, which had a plethora of information about CC. Many of the old ARRL handbooks of that era discussed CC as that was the only allowed radio operations during WWII.
My grandfather willed them to me and I have a huge box full of them.
To be honest, at first I was not really interested in broadcasting, or all that much interested in radio or CC transmission. I was more interested in high voltage Tesla experiments creating lightning bolts 20 feet long and scaring the entire neighborhood!
Some of the experiments involved generating up to 500KV on coils standing 15 feet high. Fortunately there was PLENTY of room in the back yard to build such monstrosities.
But as time went on, the interest in radio slowly started to come forth in me and it's been at the forefront ever since.
RFB