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corresponding with a couple of guys "in the know"... it's possible to connect two UHF / VHF astro spectras to form a repeater...


anyone want to try this?




doug

It sure would be nice if you could do it this way, much cheaper than buying a real P25 repeater. It would be a really nice way to slowly get a few more P25 Ham repeaters on the air.

Well, while I am not in a position to try this, due to LACK of funding and other stuff....

That sounds like a great project, and I hope that somebody can undertake it. I know I'd have to be the first to put a P25 amateur repeater together in my area, if this was a semi-affordable and reliable way to do it.

Jay

I'm gonna try it, one of these days. We have a spare 800MHz Astro Spectra in-shop, and occasionally hold several others for weeks/months at a time. The accessory connector leaves a lot to be desired, but a few mods could make it much more user friendly.

I've been unsuccessful in trying to get the Spectra/MSC/LCS (basically, any SmartZone capable radio) to pass Pocsag data, (square wave) even at a low-level fed straight into the exciter. The CDM series passes it no problem.... but, the Astro digital signal is in C4FM format, which actually looks like "messy analog", not a square wave. It in turn needs to be converted back into a digital data stream by the receiving radio. So, the key is to pass the C4FM successfully between radios. Probably not the easiest thing to do, but possibly easier than Pocsag data. The other option is to take the signal once it's been converted to the digital data stream from the recieving radio, and feed it into the transmitting radio's modulating circuitry (back to C4FM) & put out on the air. That would be more desireable, as it would in theory not corrupt the data stream. Going from theory to reality may prove difficult, but we all like a challenge, right?

Todd

Placing two ASTRO Spectras back to back to attempt to make a P25 repeater will entail reconstructing the digital waveform, and then re-transmitting it. This is no simple task!

Next, a controller to handle these functions will need to be designed and built.

Getting the RF to work would be a horrendous taslk. Getting the digital processing and audio circuits to work, and sound good, might be prohibitively complex.

This will require untold hours and costs!

Why not just buy a used Quantar on eBay, like emo did recently? A fellow on one of our local 2 meter repeaters was advertising on Saturdays swap meet a VHF Quantar in 10 of 10 condition for $2,000. He sold it on Saturday night for $1,700.

Why screw around with the mobile Ribe Goldberg arrangement that would be a joke compared to a real Quantar? Consider the fact that 2 ASTRO Spectras will likely cost as much as this Quantar repeater sold for!

If someone is hell bent on spending a long carer trying to make a P25 from 2 ASTRO Spectras, you might save a lot of effort by contacting the Chicago chapter of the MARC. If it's doable, these guys will know. (Of course, they operatre a P25 Quantar on 440 MHz ham freq in Chicago---it works great, too!)

Wow, I had no idea that you could even get a Quantar that cheaply, so I never even bothered to look... hmmmm

Keep in mind that if one pops up, you best JUMP on it.

I'd budget something like $5,000 to $8,000 to be realistic if you want to get one in the next year or so. You might wait half a lifetime to find another $1,700 Quantar in 10 of 10 shape.

I believe that Xmo had commented that he saw a Quantar on eBay for $2,500 (about the same as a local ham club he sited paid for their ICOM repeater). I think (not sure) that Xmo recently posted that he managed to buy a VHF Quantar from eBay, but he didin't mention what it went for.

I know that a new Quantar repeater (2003 list prices, PRIOR to Motorola's pending price hikes) is $22,000, plus Tax, if you get the Conventional, UHF 110 watt, with ASTRO modem, battery back-up capability, Tripple Circulator, factory duplexer and 30 inch cabinet. Even this price leaves out a TON of additional options that would further (and substantially) jack up the price.

Larry

You could either get a Quantar or you could just use a GE MastrII - look at this:

"The RMRL Goes Digital"

"Another interesting feature that was added to the RMRL 145.220 repeater during the rebuild was the support of digital voice repeat. There has been much discussion of digital voice modes recently. See pages 28-32 of the January 2002 issue of QST for a digital voice primer. The 145.220 repeater supports the APCO Project 25 standard for digital audio. This is an open, non-proprietary standard that supports many features. The most important aspect of the APCO-25 digital standard is that because it is an open standard, ALL radio manufactures are able and encouraged to build radio equipment to this standard. This will allow digital radios produced by different manufacturers to interoperate with each other. The 145.220 repeater is configured to operate multi-mode. This means that if you transmit to it with a normal analog FM signal, it will repeat your signal with a normal analog FM signal. And if you transmit to the repeater with an APCO-25 digital signal, it will repeat your signal in the APCO-25 digital mode."

"The repeater still consists of a GE MASTR II repeater with an S-COM 7K repeater controller. "

http://rmrl.hamradios.com/rmrl_news/rmr ... igital.htm

They must have a real techno-wizzard in their group!

ASTROMODAT wrote:Placing two ASTRO Spectras back to back to attempt to make a P25 repeater will entail reconstructing the digital waveform, and then re-transmitting it. This is no simple task!

No "reconstructing" involved. At least, none that doesn't already take place internal to the radios. Let the receiving radio do it's job, and convert the C4FM to digital for you. Then, re-route the data stream from the input of that radio's tx modulator into the transmitting radio's modulator. The transmitting radio will reconvert the digital back to C4FM & put it out over the air. It shouldn't care whether the data is coming from it's own receiver, or another radio's.

ASTROMODAT wrote: Next, a controller to handle these functions will need to be designed and built.

Controller for what? Keying the tx radio? Simple COR is all that's needed.

ASTROMODAT wrote: Getting the RF to work would be a horrendous taslk. Getting the digital processing and audio circuits to work, and sound good, might be prohibitively complex.
This will require untold hours and costs!

Quite possibly. This where theory & reality start to clash.

ASTROMODAT wrote: Why not just buy a used Quantar on eBay, like emo did recently? A fellow on one of our local 2 meter repeaters was advertising on Saturdays swap meet a VHF Quantar in 10 of 10 condition for $2,000. He sold it on Saturday night for $1,700.

Ah yes, the booming used Quantar market. That's why nobody is ever on this board complaining about the cost of Quantars! They're a dime a dozen. I assume you'll be picking up a bunch of these bargain babies for your upcoming system upgrades? Thought not.

ASTROMODAT wrote: Why screw around with the mobile Ribe Goldberg arrangement that would be a joke compared to a real Quantar?

Why does anyone on this board, ham or otherwise, try to do this? Number one, to see if they can. Number two, to get 90% of the benefits of a "real" repeater at a fraction of the cost (new).

ASTROMODAT wrote: Consider the fact that 2 ASTRO Spectras will likely cost as much as this Quantar repeater sold for!

That Quantar, and that Quantar only.

ASTROMODAT wrote: If someone is hell bent on spending a long carer trying to make a P25 from 2 ASTRO Spectras, you might save a lot of effort by contacting the Chicago chapter of the MARC. If it's doable, these guys will know. (Of course, they operatre a P25 Quantar on 440 MHz ham freq in Chicago---it works great, too!)

I think much of the success of such a project will depend on the level of technical information (service manuals, schematics, etc) available for the Astro Spectra radios. Block diagrams won't get anyone anywhere in this case. It should be possible. I attended a technical workshop on the Quantar. It is truly transparent, and functions much like I described above in the two-radio scenario. I also attended a workshop on Astro IMBE. It was a real eye-opener & a good overview of what's really going on in the Astro radios. The audio in an Astro radio is always converted from analog to digital, then either into C4FM (in digital mode) or back to analog for analog mode. Since these conversions are always taking place with no noticeable degradation in audio quality, two radios should be able to do the same steps seperately. I don't plan on spending a career on it, a few weeks on & off at the most.

Todd

Todd, I sure hope all goes well on your perpetual motion machine. A lot of other folks are also working hard on this, even as we speak.

Regarding the GE Master II repeating P25, I don't believe it. Sorry. The Master II is like a Micor---both are very old vintage analog FM machines.

Yeah, that GE MastrII thing is kind of odd... they don't even bother to say how they acomplished such a task.

Now I see the light. Yes, I'm sure breaking one of the laws of thermodynamics is exactly like making an Astro repeater out of two radios that already have the necessary circuitry to support the idea. What was I thinking?

Like the hope for perpetual motion, Todd, I think you were pipe dreaming of a cheap P25 repeater. Keep your daytime job and save up for a real Quantar. It's a lot more realistic.

I have no need to save up for a real Quantar. I am not a radio hobbyist. I am a communications technician who works almost exclusively on Motorola radios and systems, though I have no desire to use radios outside of working hours.

The Astro Spectra repeater has piqued my interest, simply because I think it can be done. I either have, or am able to obtain at no cost to myself, the materials & resources needed to at least try it out. Whether I will or not remains to be seen.

I am speaking from the standpoint of attending technical workshops and actually seeing technical literature on Astro IMBE radios, & schematics of Quantars. You have likely done nor seen either one, and thus speak primarily from a position of ignorance on the subject. No offence intended, I can tell by your posts you are intelligent & may know a great deal more than myself about any number of subjects. I just don't believe this is one of them.

Concerning over-unity machines, check out the following links and try to think outside the box:

http://www.cheniere.org/megstatus.htm

http://jnaudin.free.fr/html/meg.htm

Todd

$22000 for a Quantar?

We just got ours via UPS the other day for about $13000ish..(will have to look up the invoice)
Duplexer
VHF
125 Watts
CAI
Secure ready (the secure part of the system comes next budget year with the new consoles, DIU etc)
X269 - ENH: SPECTRA TAC CONVENTIONAL 1 0 0
X530 - ADD: 125W QUANTAR, VHF (132-174MHZ) 1 0 0
X580 - ADD: REPEATER OPERATION 1 0 0
X806 D - ENH: CONV ASTRO CAI OPER QTQR 1 0 0
X153 - ADD: HARDWARE, RACKMOUNT 1 0 0
X436AA - INC: MANUAL, FUNCT QUANTAR VHF 1 0 0
X131AB - INC: EXCITER, VHF RANGE 2 1 0 0
X333AB - INC: RECEIVER, VHF RG 2 1 0 0
X43AA - INC: MOD. POW SUPP HP STD 1 0 0
X187AA - INC: CABLE, DOMESTIC POWER" 1 0 0
X163AD - INC: PNLS, BLANK VHF/UHF 1 0 0
X222AB - INC: FRONT PANEL, CNTRL BD 1 0 0
X249AW - INC: CABLING PRPHL-STD QTAR 1 0 0
X142AA - INC: RF I/O ALL BNDS 1 0 0
X621AY - INTERNAL OPTION 1 0 0
C831AA - INC: CARD CAGE 1 0 0
X216AA - INC: WIRELINE INTERFACE 4 WR 1 0 0
X842AB - INC: CONV/6809 ETHER TERMN HDW 1 0 0

Pj, I have the Nov 2002 R3 and I am quoting lsit prices. It's simple arithmetic. You must have a nice discount! Wish I could get a discount but we don't have the volumes.

A later Mastr 2 with the FM exciter and 2c icoms could likely be made to repeat a P-25 signal with little modification. If the RX to TX audio path was resonably flat down to say 40 HZ and up to 3000hz, it should go right thru.

I have access to such a repeater, we will see what happens as soon as I can program two mobiles for it.

Interesting thread....

Some random thoughts (from a point of relative ignorance):

1) Has anyone tried contacting the folks over at the Rocky Mountain Radio League to see just what they did?

2) Their site indicates that they upgraded their machine. Think this is still the current P25 repeater? http://rmrl.hamradios.com/repeaters/guy ... _large.jpg

3) Given that they indicated that the repeater will not support selective signaling, etc., I would think that they are not actually running a truly transparent digital repeater, but rather are handling the audio as analog between the receiver and transmitter.

4) For home brewing a true P25 transparent repeater, Todd sure sounds like he has the right idea.

What Todd is proposing to do does make sense. You would think that it would work better to recover the digital signal in your receiving radio and re-transmit new digital modulation as opposed to just passing the C4FM signal through as audio. It would seem probable that some distortion of the data would take place which could result in higher BER and reduced range.

Then again - maybe not. That is the whole point. I understand exactly why Todd would want to make a repeater out of two mobiles - to learn how thinks work - to further your knowledge.

One other point. Someone may be thinking - why not just take the analog receiver audio through something like a RICK and connect it to the transmit radio. That is not what Todd is proposing.

His idea is to take the ASTRO signal as data from one radio to the other and bypass the VOCODER. The real question is: can you get at the ASTRO signal as data? Or are the D/A and VOCODER functions so tightly integrated into the DSP on the VOCON that you can't?? Maybe Todd will pass on his results.

I think that would be the key to success. Motorola warns against double VOCODING. For example, this would occur in a console patch of two digital channels. The book says this will result in degraded audio quality. How degraded?? I have no idea - I'll have to try it and see (that learning thing) It might be tolerable for short duration patch events, but undesirable as a repeater.

Pj, you left out a lot of options that I need for my Quantar application that will make your price close to my list quote:

Add on the following: UHSO (required, per xmo's post for 12.5 kHz operation), Batrtery Back Up capability (I would think this is required for Public Safety, but it's pretty cheap so no big deal here), tripple circulator, 30 inch cabinet, ASTRO 9.6 kb/s modem (you need this so your DIU 3000 can communicate with the remote Quantar).

These above options will add about $6,500 to your $13,000 plus quote (not including the $10,000 per DIU). You are now at $19,500 plus, which is only about 10% lower than my $22,000.

I would guess that your 10% lower is because either 1) you ordered it last year (they just added an additional $1,750 for IMBE, above and beyond what they charged for IMBE last year, so this puts you at $21,250) or 2) you have a small discount or 2) you didn't add sales tax. Either way, a Quantar is $22,000 list price, and this leaves out TONs of additional other options!

Pricey little buggers, aren't they?!

Larry

Wow! I just caerefully added up the Quantar current pricing, and Pj it's even worse than I thought!

If you order a UHF 110 watt Quantar with the following options:

Conventional UHF ASTRO IMBE
30 inch cabinet
factory duplexer
UHSO
Tripple circulator
Peripheral box (necessary to house the additioanl double duplexer)
ASTRO modem
batterty backup capability (not including batteries)

Adds up to $22,482 list. Then add $2,001 sales tax (8.9%) plus $500 for shipping and insurance and we have $24,983 total.

So, there you have it: 25 Grand for a new Quantar, and that leaves out a whole bunch of additional other options that could easily bring the total to $30,000.

This does NOT include the yet-to-be-announced 2003 price increases (other than the $1,750 increase in the IMBE price that they announced in November, 2002). I'm hearing that the 2003 price increase is going to be a whopper, too! I expect this same Quantar could hit $30,000 (all told, with tax and shipping) for my configuration, and maybe $35,000 if it were to be fully decked out. Boy, a guy could really use a discount!

Larry

Ok... curiousity has set in....

2 ways I see this happening.

1 - RICK-like configuration.

Connect the TX/RX from one and do the same to the other. Sounds like step one, see how the audio is. If it sounds good, great! If not... proceed to option 2.

2 - Todd's idea of interfacing data streams.

I have a few questions for you Todd (in open forum for other's brainstorming.)

1: The analog gets put through the DSP support circuit and then to the DSP for "cleaning." Then (for analog) it gets sent back again to the DSP support for D/A conversion. (I think.) One would assume that somewhere betweend the DSP support and DSP is where the "tap" would go. I seem to lose in the schems. the path of the correct data to tap between the DSP support and DSP.

2: Which side to tap? The DSP support to DSP or the other way around? Does it depend on whether you're looking to pass RX vs. TX?

3: Would you have to actually cut the data streams trace and enter in the other's for processing? I'm assuming you would to prevent clashing.

The concept seems simple enough, just where and what to pass between the radios from a data standpoint.....

The quest continues....

tpg

I still think you guys might save a bunch of time by contacting the Chicago MARC group. These are the Motorola EE Hams, mostly from the Motorola Base Station group as well as the SP Base Products Group and Secure Group, who live and breathe Quantar for a living. They play with Quantars on the Ham bands on their daily commutes to/from work. If it is feasible to connect 2 ASTRO Spectras back-to-back to make a P25 repeater, I would guess these guys may have either done this already, or they have thought about it, or perhaps have looked into it (in some detail) and would be an excellent source of information. Still, I do know that the Motorola Ham groups in Chicago and Dallas/Ft Worth are both using regular Quantars.

Also, you might want to contact the Dallas/Ft Worth MARC group. These are some of the ASTRO Spectra folks, so they may also be helpful in your quest. They also operate a P25 Quantar on the Ham VHF and UHF bands.

Larry

Thanks for deciding to be helpful, Larry.

As far as what I proposed, I have no further info right now. I really only began to think about it yesterday, when the concept was brought up in this thread. I'm not going to concern my self too much with vocoding/DSP's & whatnot. Let the receiving radio do 90% of the work. Receive the C4FM, convert it to a digital data stream, process it in whatever way it does. The next step, if it's A Quantar in Astro digital mode, would normally be to simply route it to it's own C4FM modulator, then onward to it's transmitter. The trick is to emulate the Quantar by tapping the datastream in the first Spectra, and routing it to the transmit modulator in the second radio. Is there an accessible spot on the vocon to tap from? I don't know. And yes, it will require cutting traces in both radios, if it is possible.

Is this possible? I really don't know at this point. These are strictly my first thoughts on the subject. I likely won't be posting anything further until I order in the detailed service manual for the Astro Spectra. Hopefully it'll contain the information needed for this project. My main goal at this point is to put forth ideas & maybe others on the board will be hit with inspiration as a result.

Todd

------I edited this post. I confused even myself the first time around, and was thinking it terms of Quantars for much of it-----------

Some features that are included in the APCO-25 standard but are not enabled
on the 145.220 repeater are encryption, data transfer, individual calls
(unit-to-unit private calls), telephone interconnect, and emergency calls.
The repeater can be accessed in the digital mode using a NAC (Network Access
Code) of $293 with a Talk-Group of $FFFF. This talk group talks to all
other talk groups.

i'M NOT TRYING TO ACCESS THE SYSTEM ABOVE, BUT i WANT TO KNOW HOW I WOULD SELECT SUCH A T/G IN CPS 2.0, As I thinkit would make it a bit harder 4 someone else to listen to our ops since we're not alwyas secure. How can I program the t/g?


Anyone?

Since this is a Ham repeater implementation of IMBE voice, why the P25 issues?

For instance, with ASTRO digital squelch, why is there a need for a NAC and/or a Talk Group? Can't you set it up so neither a NAC nor a TG is needed to access the repeater for simple IMBE voice on a P25 repeater?

Larry

I don't really wish to double post, but anybody reading this thread, it more or less continues in the one below:

http://batboard.batlabs.com/viewtopic.php?p=59727#59727

Todd

As far as talkgroups making it "private" where others can not hear it, all they need to do is either program their radio digital CSQ or hold the monitor button to hear all Astro talk groups.

George

Here's another idea that may work:
Don't even mess around with the demodulator circuits in the repeaters receiver or with the modulator circuits in the repeaters transmitter. Try it this way.

Take the receivers IF output (which is still P25 RF only translated down to a lower frequency) and feed it into a mixer, on the other port of the mixer feed in an LO signal to get you to the repeaters final transmit frequency. For example: assume the repeaters receive frequency is 150 MHz and 151MHz for the repeaters transmit, if you used a receiver with as an example a 45 Mhz IF then feed a 196 Mhz Local oscilator signal into the above mixer, the 45 MHZ IF mixes with the 196 MHz lo and finally use a bandpass filter to select the desired output frequency of 151 MHz. Mini cuircuits has some nice cheaply priced mixers which would be perfect for a project such as this.

The mixer output then goes into the transmitters amplifier circuits way after the modulator stages, remember we don't need to use the transmitters audio or modulators circuits were only interested in the RF power amplifiers.

You are only translating the IF signal which is still P25 RF(45 Mhz is still RF) to another RF frequency which is the repeaters output frequency. You would probably need to use the demod circuits in the repeaters receiver to get a D.C. level at some point to use as a transmit carrier operated signal but that's all you'd need the receivers demod circuitry for.

This may be a better project to try as opposed to chopping apart some spectras for a repeater, ouch just the thought of chopping apart some Astro Spectras makes my stomache ache.

You may need to change the LO injections from high side to possibly low side to get the P25 data correct, I'm not 100% sure on this but it may be required. I haven't sat down to work out the math.

Another thing I just thought of, you'd need a receiver strip with a fair amount of AGC to keep the 45 MHz IF feeding the mixer at a fairly constant level but you could test the theory by taking a P25 HT and setting at low power then padding the HTs output down firther so have say about -10 dBm output for feeding into a mixer, mix this with a stable local oscillator signal of your choice and then feed the mixers output into say a R2670 analyzer set at one or both of the resultant mixed frequencies and see if the R2670 will demodulate the P25.
Any ideas on this suggestion ?

Mike

Yes Mike, I like the sounds of that theory. It would eliminate the double vocoding problem, if it works. The mixer would have to be of fairly high quality, to handle the discrete 4-level modulation (C4FM) properly.
My next step is to check out a similar possibility using the 2 Spectras. I will attempt to find a point between the receiver's ABACUS II back end, and the ASFIC, which will (i think) contain the fully discriminated discrete 4-level modulation. If that could be steered into the tx exciter circuitry, all should be well. Hopefully that nasty thing called work won't get in my way too much next week to get started on it.

Todd

"Any ideas on this suggestion ? "

-----------------------------------------------------------------------------------

I am sure you can make this idea work - under certain conditions. Frequency translator systems are used - in TV broadcast for example, but I think there is a basic problem with the idea of a 'translator' type of P25 repeater.

Your translator would probably be keyed when the receiving radio gates it's audio on (sort of a digital COR) A properly working P25 receiving radio should recover data with less than 5% BER at somewhere in the neighborhood of 5dB C/N [Carrier to Noise ratio].

Now your transmitter is retransmitting the data along with all that noise at a high power level. A 40 Watt repeater could easily be transmitting over 10 Watts of noise. Even at high receive C/N ratios your spectral occupancy will be way out of compliance with FCC rules.

About that RMRL digital ham repeater...

I use it everyday. The repeater is made from EFJ portable radio controller boards, with GE master II RF section. The signal goes through the D/A conversion twice, which is unique to this homebrew repeater. I don't know any true details, though, but I can ask. I'm a member of RMRL, and know the guy that built the repeater. Maybe he will share some of the technical details of how he built it, and would allow me to post them.

Also, I'm not sure why it is setup with a single talkgroup, rather than just CAI. If you don't transmit with the talkgroup, you will not bring up the repeater. Might be something unique to how the EFJ boards were linked. Oh yea, you get a hand-time with this repeater.


-Yosh

You actually don't need Astro radios to do a pure repeat. I had a repeater on the air in Binghamton, NY from May 1995 until 2001 that would repeat VSELP, and IMBE. The repeater was composed of two GE Delta (Synthesized) radios. On squelch open (yeah, I know, Astro sounds like white noise, but there's really not alot of high (>5khz) frequency component to it, so the squelch worked), the discriminator output of the receiver was tied directly (almost) to the varactor in the VCO in the transmitter, the normal input to the varactor from the audio processing was opened, and the transmitter was keyed. The filtered audio was run into a delay (guts from a MRTI 1000) line. The purpose of this was to keep from losing the chunk of speech when an analog radio used the repeater, and the repeater put the normal audio path in place. If the squelch opened, and there was constant high level audio, it was assumed that Astro was present, and the signal path was left as is. If the squelch opened, and there appeared to be breaks in the audio - like speech - the direct receiver to transmitter connection was broken, and the buffered (delayed) audio was routed thru the controller so the patch, courtesy tone, and ID would work. The delay was speeded up so the delay for normal traffic was only about a quarter second, rather than the normal half second that the delay board does. Gain was adjusted so that in to out deviation was very close to equal. If the machine was in the process of IDing when the logic decided that Astro was present, that would be terminated. Range thru this repeater wasn't bad - less than the Quantar, but not bad considering there was no re-clocking occurring. Distance from the mobile (low input to the repeater) seemed to be more critical than the distance from the repeater to the mobile. If you went to analog mode, when the Astro got real crappy, there was definitely noise over the path. BTW: This was all on High Band. Actually, my hack was on 146, and the Quantar was on a 153-161 split.