HF Repeaters

[Lauri-CoyoteFrostbite]

Yes, its too bad some of these early radios didn't survive, but so many were 'bread-boards' and if that wasn't as temporary as they come, they were also the instant fodder to be cannibalize** -- parts for the next project.

An aside-------
I have a collection of radio ephemera that spans over 120 years.... from the unofficial log books of my great aunt who was a Marconi Girl, early De Forest "valves'-- to my pride - a Maggie wire receiver (of RMS Titanic era.)
I stopped the collecting of radio stuff with the late 1930's (a Hallicrafter's S-20R)--- for; "just where do I put it ?"
I can sympathize with the curators of the K6MYK machine.


It would be interesting to try an old AM repeater however.... kind'a like spark gap. We 'fired up' a pair of Heathkit Two'ers not long ago and had ball stepping back into a simpler time of ham AM radios ***

Lauri




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**Oh, how I loved that term ! As a member of Air Force MARS my grandfather used to delight in all the surplus equipment available. I still have some of the official paper work he kept for each piece issued him. It says that the 'whatever' was to be either return to the Air Force if no longer needed, or "cannibalized for parts. "
I have a feeling the cannibals always won.


***Any old timer will probably cringe at that idea though, if they operated 75 metre phone... it was a supposed heterodyne city !

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[RFI-EMI-GUY]

"............they would have probably used the first known amateur repeater K6MYK which was 2M AM and built............" prcguy



Awesome !! ---Where to start ?....

This morning I got a call from my dad who has lately turned into a morning person and who doesn't seem to care that there is a two hour time difference between us (he's on east coast.) I am worthless at 5.30 AM. But that aside, I took some drowsy mental notes, with his promise of more historical pearls later (and at a better hour.)

The AM repeater was one of his gems mentioned and I am pleased to see it here.

My grandfather and his friends were quite aware of how niffty VHF repeaters were as far back as hams were aware of VHF. He told of listening to police calls on the high end of the AM broadcast band that were repeating traffic from the squad cars transmitting on low band VHF. The headquarter's station was high powered, approximately on 1700KHz .... an AM station that broadcasted to the cars..... they would responded on low power VHF. No details on the equipment but what ever it was it sparked ideas.

Mobile FM equipment was available in the 1960's-- which is the time frame for my grandfather's VHF experiments-- but it was prohibitively expensive. It would not be until the FCC required VHF system to go "narrow band" that there would be a phethora of surplus FM radios to spark a radio revolution--- but a lot more on that to come later.

Back to the AM repeaters.

One of the things necessary for repeaters is to have something to repeat. There were plenty of Technician class licensee's-- Six Metre AM was a very hot band back in those days... a fertile ground to experiment upon.

Drawing on the experiences of listening to those police radios, my grandfather and friends set up a simple AM repeater system. He built the repeater- which basically was a modified CB transceiver as the IF --using a TV tuner tuned to some frequency in the low 50MHz range. Using a "nuvistor" (Remember those cute little metallic tubes - 6CW4's, 6SD4's? They were the hottest things until V/UHF transistors) --preamp made it a 'hot' receiver (or so I am told.... but Hey ! this was 1960's standards, in the days of true home brewing.)
The CB radio had a squelch and its audio fed a a low power AM transmitter operating in the high end of 53MHz. What made this interesting was they squelched the audio, but not the carrier. It was left on continuously. In the days before crystal control that allowed even regenerative receivers to find the repeater and stay "tuned in" - and it provide a beacon of sorts to adjust your equipment to (no mention of Channel 2 TVI however--- ignored ?).

The repeater used separate antennas and some sort filtering to keep the 53MHz out of the receiver. Supposedly the low power and frequency separation was not a big de-sensing issue.
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These hams played with the system for "awhile" according to my father; This was in the Washington DC area-- he said they covered a "several mile radius of Andrews Air Force Base/ Camp Springs/ Clinton area."

But other than a novelty this repeater went nowhere---- and now is just part of my family's ham history. It wouldn't be until the FM Sweep later on, that serious VHF repeaters would take off.


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Lauri

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That is some pretty cool stuff indeed. Making something from surplus equipment has always been an incentive for Ham experimentation.

On the FM side, there have been a few "Narrow-banding" mandates over the years. The recent one +/- 2.5 KHz deviation, that followed +/-5 KHz that I was familiar with throughout most of my career. But there was before that. +/- 15 Kc and so I am told, once +/- 30 Kc. Maybe +/- 60 Kc when Edwin Armstrong was FM God.

 

[Lauri-CoyoteFrostbite]

Ah ! the switch to 30Kc bandwidth !

That was a treasure trove for hams. Almost overnight there was a flood of FM radios that were just not worth the $'s to narrow band.... (like they were narrow by today's standards. I can only image ---imagine since I will have passed in my chips by then--- what 'narrow' will be in 60 years ) ***

Growing up, our house hold was filled with quizz-i-cal electronics- quite a few were former FM mobile radios like RCA Carfones, Motorola-mystery models, some GE radios--- my dad was a MARS member like his father--(and I well remember their tales of Saturday morning trips to Bolling AFB when "The Colonel" --my grandfather, would load up the family VW van and bring home surplus treasures from the MARS warehouse---- much to to the angst of my grandmother .)

One of those treasures was a low band RCA Carfone they cannibalized into a beautiful 6 metre DSB linear amp. It used the radio's circuitry for a final; a pair of 807's pushed to their limits ...where the plates would glow bright red on voice peaks.

"Is that bad for the tubes?" I recall asking my grandfather years later

"If they fail we have plenty of spares" was the reply
(Surprisingly you can kick the snot out of 807's and they just keep smile at you )

------------ Today his son, my father-- still has that amplifier, and for all I know, with the original 807's.

But back to FM


It was a revolution in ham radio. Almost overnight CQ, 73 magazines was running a tonne of articles on converting commercial radios to amateur service.

146.94 and 52,525MHz were the golden simplex frequencies. It would not be until repeaters that "94" turned to "52" as the universal simplex channel. "525" is still the 6 metre FM caliing frequency - (and the one I listen to all the time-- very quiet btw.)
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And do I broach what could be the 10 metre --HF--- part of this marvelous revolution ?

First, another glass of wine


Lauri



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*** It was a wonder-us era, wide band FM !... you have to experience that wideband audio over an equally wideband receiver to appreciate what has been lost,..................... errr..."changed for the better."

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[RFI-EMI-GUY]

 

[K6OQK]

Repeaters generally don't drop off as soon as an in-coming carrier drops; they normally have a delay of a few seconds. So, for a SSB repeater it would only be necessary to have a 2 or 3 second delay, which would carry through a typical transmission by a user station.

To keep the repeater from keying up by unintentional signals, a PL type of tone within the audio passband of the repeater receiver could be used. Depending on the amplitude of the tone, it by itself, would / could maintain enough carrier to keep the repeater keyed up during a transmission.

Burt, K6OQK

Repeaters use carrier operated switching to turn the repeat function off and on. The presense of a carrier turns the repeat function on.

With no carrier, single sideband is difficult to 'repeat'. The linear SSB amateur satellites use crossband transponders. Transponders blindly up-convert or down-convert one frequency to another. Using crossbanding eliminates the need for extensive filtering. Linear Satellite Frequency Summary – AMSAT

This could work on HF.. Go in on 20 meters and get transverted out on 40.. (And vice-versa). But what would be the point? HF by its very nature is capable of covering long distances without the need of a repeater. Just use the frequency that provides the best propagation for the job at hand.

Repeaters generally don't drop off as soon as an in-coming carrier drops; they normally have a delay of a few seconds. So, for a SSB repeater it would only be necessary to have a 2 or 3 second delay, which would carry through a typical transmission by a user station.

To keep the repeater from keying up by unintentional signals, a PL type of tone within the audio passband of the repeater receiver could be used. Depending on the amplitude of the tone, it by itself, would / could maintain enough carrier to keep the repeater keyed up during a transmission.

One other thing regarding HF repeater thinking... On Saturday mornings a group of us O.F. meet on 40-Meters for a round table. There are times when we cannot hear all of the 5-10 stations in the group. In these cases we usually use one of the On-Line SDR's such as KFS. I always tell other's that I'm listening on the KFS Repeater. Yes, we are accessing it via an Internet connection, but it could just as easily be built using a split site repeater with a bunch of miles between the transmit and receive site; enough distance to avoid overload of the repeater's receiver. Just thinking out loud here. Of course the receive site would have to be pretty quiet, and the transmit site would have to make enough signal to overcome the whole purpose of needing a repeater. Not very practical. KFS and others do a pretty admirable job, and they don't have the propagation issues that an RF transmit repeater would have via the low bands. Fun to ponder over.

Burt, K6OQK

 

[Lauri-CoyoteFrostbite]

Sounds to me Burt what you are doing in basically full break-in duplex, using geographical separation to permit same frequency transmit/receive without blowing out your ears and your receivers.

When I was working we would often do the very same thing--- utilize a certain advantageous transmitter site and a another remote receiver location all linked by a satellite -- it was neat--- I could be in the desert southwest, up link to a receiver in Norfolk Virginia-- and then to my favorite, a 10 KW blowtorch at "D-Ville" (the USAF transmitter site in Davidsonville Maryland)--- I could hear all the other stations and myself perfectly-- on the same frequency HF SSB --- it was just like a telephone conversation with full duplex.

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[w2xq]

This could work on HF.. Go in on 20 meters and get transverted out on 40.. (And vice-versa). But what would be the point? HF by its very nature is capable of covering long distances without the need of a repeater. Just use the frequency that provides the best propagation for the job at hand.

I don't remember the year any more--probably the 1970s--but I recall a satellite repeating 10m to 15m (or vice versa) CW. I could hear it when antipodal to me. I think I made a few contacts on it. But I'm not up to digging through the myriad of my ARRL logbooks...

 

[RFI-EMI-GUY]

Repeaters generally don't drop off as soon as an in-coming carrier drops; they normally have a delay of a few seconds. So, for a SSB repeater it would only be necessary to have a 2 or 3 second delay, which would carry through a typical transmission by a user station.

To keep the repeater from keying up by unintentional signals, a PL type of tone within the audio passband of the repeater receiver could be used. Depending on the amplitude of the tone, it by itself, would / could maintain enough carrier to keep the repeater keyed up during a transmission.

Burt, K6OQK

(snip)

There was a company, Securicor , if I recall, who manufactured a duplex ACSB repeater for the commercial 220 MHz band. They used a pilot tone to control and net the repeater. The pilot tone was notched out in the recovered audio. I do recall a ham in Miami experimenting with DPL (DCS) on the HF SSB so he could have a squelch at his folks home in Venezuela. Not sure if that worked out.

That said there are a number of voice activated squelch circuits which recognize human voice, Naval Electronics being a famous one. I have an old JPS product that has such a circuit.

If the repeater RX audio is first stored in a simple audio delay and the repeat controlled by voice activate squelch, any delay in recognizing voice can be mitigated. The major problem is with the transmitting station and repeater receiver BFO being "netted" on frequency. There have been some experiments with DSP to recover the center frequency of the BFO by statistical analysis of the voice components. No doubt there is a product somewhere.

 

[K6OQK]

Repeaters use carrier operated switching to turn the repeat function off and on.. The presense of a carrier turns the repeat function on.

With no carrier, single sideband is difficult to 'repeat'. The linear SSB amateur satellites use crossband transponders. Transponders blindly up-convert or down-convert one frequency to another. Using crossbanding eliminates the need for extensive filtering. Linear Satellite Frequency Summary – AMSAT

This could work on HF.. Go in on 20 meters and get transverted out on 40.. (And vice-versa). But what would be the point? HF by its very nature is capable of covering long distances without the need of a repeater. Just use the frequency that provides the best propagation for the job at hand.

From Burt, K6OQK...

As I think I mentioned elsewhere, a Single Sideband (SSB) Repeater could be made to work very well. Most repeaters have a hang time of 5 or more seconds before dropping off. If you built a carrier (signal) operated relay that keyed on the presence of the first bit of SSB audio, the repeater's hang time would carry through most of our (my) mumbling and speech pauses with no problem.

Most people think of repeaters needing cavities, and for bands like 160 meters the cavities would have to be grain silos! Not true. Proper filters could be built out of lumped constants such as coils and capacitors with networks similar to those used when combining AM broadcast stations in a combined antenna system. Properly built, these networks can provide excellent isolation. But, then what's the point.

I've been part of a group that meets on 40-Meters every Saturday morning. Sometimes conditions don't allow us to hear everyone in the group. So, what do we do? We use a repeater. The repeater is also known as the KFS Web SDR. It works great as a repeater for us.

Burt, K6OQK