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Mike Nowlen, WB4UKB
[email protected]
RCA Series 700/1000 Low Band (42-50 Mhz Split) to 6 Meter Amateur Conversion
Update 2/7/97
Documentation Required:
To save gobs of time and frustration when tuning the PA, strap a rubber band over the mic PTT to keep the transmitter keyed and use two INSULATED SHAFT tuning tools at a time on each set of paried adjustments. Do not use regular screwdrivers as the cap rotors are hot and sparks will fly.
Troubleshooting:
If the transmitter power output does not reach specification, check
to insure that there is 1 watt or greater at the output of the transmitter
multiplier board using a 50 ohm wattmeter.
Transmitter Audio Boost Modification
Part Required:
Copyright © 1996, Mike Nowlen, WB4UKB
> I guess I'm confused as to what I would need to order to recrystal the existing element pair for another frequency. If I wanted to recrystal for, say, 52.0 transmit and 53.0 receive, how many crystals would I need? Two or four?
You need two. One for transmit and one for receive. Transmit and recceive do not have to be the same freqrequencies.
>What cuts would they have to be and what capacitance (i.e. AT cut or series-resonant, how many pF capacitance, etc)?
Just tell the supplier what kind of radio you have. (RCA Series 700; 500's and 1000's also use the same xtals). The suppliers know how to cut and calibrate for each radio. If you run across one that doesn't know the RCA they may want you to send them a set of crystals to work from. I have had to do this on occasion. Just pull the elements apart and unsolder the xtals. FYI, all xtals in these freq ranges are AT cut with refers to the angle that the quartz is sliced. Series resonant refers to the type of oscillator circuit used.
> I would also like channel elements for 52.68, our weather backbone.
I don't have any 6 Meter crystals available for sale. The channel elements are supplied with either the original Commerical crystal or no crystal (Most have commercial 42-49 MHz crystals). They will work with any 6 Meter crystal freq. The radio will be tuned to 52.525 MHz.
> I recently purchased a Motorola Mocom70. I was under the assumption that this rig would be able to accept any crystal in the range of 25-174mhz. Is this a correct assumption. I have researched my radio, it has a serial number of U71BBA2900AA According to my research this is a 25-54mhz. range transceiver. Is this correct, or can I place a 146 Mhz range crystal in it? If not is there a modification that can be done so as I can receive and transmit in this range?
Welcome to the confusing world of bands and splits! Imbedded in that long U71 model number is a wealth of information that can really only be fully decoded with a Mocom 70 service manual. For example, I believe the 7 means high power (probably 100 watts) and the 1 means Low Band VHF 25-54 MHz like you already know. A 3 would mean High Band VHF 150-174 MHz, and 4 means UHF 400-512 MHz.
The thing you may not yet know is the split. Each band on crystal controlled FM commercial radios is divided into splits. Low band is usually divided into 3 splits such as 25-30, 30-42, and 42-50 MHz. Generally the radio design and circuits of all the splits on a particular band are the same, but the component values are different to allow the radio to tune over the range of the split. If the radio has the original channel elements in it with the frequency stamped on top, that's a good indicator of which split it is.
So, not only do you have to get the right band, you also have to make sure you have the right split. The service manuals usually have all the component values for all the splits so you *can* change the components if you have the wrong split but it is a *big* hassle. Better to trade the radio with someone that has the band and split you need.
So no, you can't put your low band radio on the 2 meter ham band.
Since most of the FM commercial radio's were not really designed to cover the ham bands, you have to get the closest split and then modify the radio, usually only slightly, to reach the ham band. For example, see the RCA low band to 6 meter ham band mod at the top of my page. You are in effect creating a new split, perhaps with somewhat reduced performance, but it will still out perform most if not all radios sold for ham use.
Mike WB4UKB
[email protected]
http://www.geocities.com/mnowlen
Bomar Crystals: 800-526-3935
D.W. Thomas: (714)892-3234 or (800)800-9625
MH Electronics: (800) 743-9825, Discounts for 10 or more.
Hi Mike
Happened to check your web page and saw you need requirements for crystals
from time. We are a manufacture of AT cut crystals and have some
of the
best prices in the country. You can check us out on our web page
@
http://www.westcrystal.com
Add us to your site if you wish.
Regards
Ernest
Having seen AF4K's list of crystal suppliers in Mike Nowlen's post related to 2-way radio information, and noted that the one I have used most recently is missing, I thought I would forward information to all for inclusion in future lists updates. I have purchased many many crystals over the past 20 years. ICM actually had a big problem and refused to acknowledge their problem related to microphonics in a repeater crystal (also very high prices!), so I switched to Bomar. I actually met Mr. Citron, the VP of Bomar who was eager to help amateurs with crystal requirements. I found Bomar's quality to be excellent but suddenly about two years ago they adopted a minimum order requirement ($50 I believe) so I switched to Hy-Q International, located in Erlanger KY, and am glad to say they have no minimum order, their price is good ($8.45 each) and quality is excellent.
HyQ tel.# 606-283-5000.
I highly suggest adding HyQ to your list.
73, Reid Brandon W6MTF
Thanks for the information. I too have noticed microphonic problems with ICM. They must use spring-type mounts.- Mike
Credits for following information * Larry Goodwin and Brian Carling*
forwarded by Stephan Rashkin
***************************************************************
Cal Crystal 714 991-1570 Waiting for more information Buena Park or
Anaheim (not sure which) California They will MAKE rocks for almost anything.
Cathodeon Crystals, Need phone number A PYE Group Company Linton, Cambridgeshire
England (Need postal code) Crystals
Crystek Crystals 800-237-3061 2351/2371 Crystal Drive Ft. Myers, FL
33907 Quartz Crystals
CW Crystals Inexpensive, but SLOW to respond. 570 N. Buffalo Street
Marshfield, MO 65706 (Crystals, $1.00 catalog)
International Crystal Mfg Co. 405-236-3741 10 North Lee Street Crystals!
Oklahoma City, OK 73102
ICM (International Crystal Manufacturing Co., Inc.) 800-426-9825 P.O.
Box 26330: 701 W. Sheridan Oklahoma City OK 73126-0330
JAN Crystals 800-526-9825: 813-936-2397 P.O. Box 06017: 2341 Crystal
Drive: Crystals Ft. Myers, FL 33906-6017
LESMITH CRYSTALS (905) 844-4505 54 Shepherd Rd, Fax = (905) 844-2274
Oakville, ON L6K 2G5 CANADA Crystals for amateur radio. VISA & MC OK.
MDM radio (708) 848-4210 Address needed FAX = (708) 848-0230. Channel
Elements for commercial 2-way radios.
Petersen Radio Co. (712) 323-7539 2735 Avenue "A" Council Bluffs, IA
51501 Crystals
Ryan Communications 412-368-3859 BOX 111E Camelot Road (QRP CW transmitter,
ready made,) Portersville, PA 16051 (and transmitter kits, crystals)
Velco Electronics (716) 924-2073 Address needed (716) 924-2136 = FAX
Crystals
C. W. Wolf Communications (406) 252-9220 Address needed FAX = (406)
252-9617 Channel elements for commercial 2-way radios.
This list was prepared by AF4K, Brian Carling - Updated 3/1/95
***************************************************************************
*
Larry Goodwin KC6WOG *
reply to... INTERNET: [email protected] * *
73 es gud DX *
AX25 PACKET: kc6wog@wb6wfh#soca.ca.usa * * --... ...-- *
Better Living Through Sound Effect Editing
***************************************************************************
Subject: Re: FS: RACAL 6790GM Military Technical Manual
From: [email protected]
(TIFFANY)
Date: 1996/04/02
Message-Id: <[email protected]>
Distribution: na
References: <[email protected]>
News-Software: VAX/VMS VNEWS 1.41twb
Organization: TAMU Cyclotron Institute
Newsgroups: rec.radio.swap
...snip....
Just in case anyone's interested, there is such a place called
National Technical Information Service and if you know the number of
the
technical manual you need, they will sell you a new one. (If it isn't
restricted...I've run across very few manuals that are restricted...)
Their phone numbers are:
(703) 487-4684
(703) 487-4841 (fax)
If you don't know the technical number of the manual you need, there
is a handy little document you can usually find at your local library
that
is a cross-reference of manuals to equipment and vice-versa...I believe
the
number of that document is DA PAM 25-1 (Dept. of the Army Pamphlet
25-1).
Just ask the attendent in the documents section to get it for you.
In the
past few years, they've only been distributing this on microfische.
Generally, technical manuals regarding radios start with TM 11-5820-####.
Repair manuals for radios start with T.O. 31R2-###...fwiw...
73...
Tiffany -- kj5gu
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Tiffany M. Bloxom DANGER!!! AGGIE SKYDIVER!!! (C-25276)
ARS: KJ5GU College Station, TX/Aggies Over Texas
Racer Elite 2000, Sabre 135, Microraven 135, Cypres
[email protected]
-or- [email protected]
GS/MU d-- H+ s--:>-: !g p? au+>++ a- w+ v* C++ U-- P? L !3 E- N++ K-
W+ M-- V+
-po+ Y+ t+ 5 jx R- G? tv b- D+ B--- e+ u+(---) h f r+++@ n- x+++@
-=For the latest breaking Aggie Jokes, dial 1-800-AGGIE-IQ=-
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
I have the following radio equiment available for sale. For more information, e-mail me at [email protected]
These are the Terms I like to use when trading over the Internet.
All items are plus shipping charges. Send Zip code for shipping estimate.
UHF GE Delta Synthesized Mobile
Radio
100Watts, Excellent condition, clean with accessories. Trunk mount commercial mobile about 14" x 13" x 2". Comes with 16 channel control head, mic, speaker, cables. Standard commercial specs. Has programmable CTCSS tones. I'll program it to the freqencies you want:. $325 + Ship
RCA Series 700 Low Band 42-50 MHz, can be tuned to 6 Meter Amateur Band, FULLY SOLID-STATE 40 Watt Mobile, 4 freq, As-is, No Accessories, 1 set of Channel Elements (no 6 Meter crystals available), see 6 meter Amateur Band conversion instructions above: with tuning instructions, 25 lbs: $40
ACCESSORIES:
Extra Set of Channel Elements (Rx and Tx): $5
QC Deck (CTCSS) without vibrosend/sponders (uses Motorola type):.$10
Lots of spare parts.....Inquire.
RCA Series 700 Low Band Table Top Base Station Radio High Split (42-50 Mhz)
FULLY SOLID-STATE Commercial FM Transceiver, 40 Watts, Operates on 120
VAC, 2 frequency (easily converted to 4 frequency). Converted to 6 Meter
Operation. Tuned to 52.525 MHz (crystals not included). With integrated
speaker, desk microphone, 1 set of Channel Elements. Tuning instructions
and interconnection schematic diagram included.
CONDITION: Very Good. Removed from service. Checked and Working. Converted
to 6 meter Amateur Band.: $125 ea, 2 Available.
ACCESSORIES: Extra Set of Channel Elements (Rx and Tx): $5
QC Deck (CTCSS) without vibrosend/sponders (uses Motorola type): $10
Lots of spare parts.....Inquire.
I have what appears to be a RCA High Band 250 Watt Amplifier. Uses 4CX250 type tube. Looks complete except no cabinet or blower. Heavy. UPS shipment may be possible if power supply is shipped seperately. It is in excellent physical condition but I have not fired it up so I don't know about operating condition.: $150
Low power version, working fine, in fair condition without accesories. No Covers. CHEAP: $40
Mint with original box and manual., Works perfectly: $675
All items are plus shipping charges. Send Zip code for shipping estimate.
Mike Nowlen,
WB4UKB
Reston, VA 20191
e-mail me at [email protected]
No calls after 10PM Eastern please. Answering machine picks up on 4th
ring: 703-716-1363:
These are the Terms I like to use when trading over the Internet.
Subject: More on the RA 6790/GM
From: Ken <[email protected]>
Date: 1996/12/23
Newsgroups: rec.radio.shortwave
I've stumbled onto a "keyboard hack" to allow reception below 500KHz on the RACAL 6790 receiver. Just enter the frequency you want, preceeded by 1MHz. For example, if you want to hear LORAN C (100KHz), hit "enter 01 100 000. Then hit "enter" 00. The 100KHz will remain on the display. All receiver controls work normally, with the exception of the tuning knob. If you turn the knob, the receiver will jump back to one edge of the normal tuning range. I just turn the "lock" on. The receiver will function down to 0 KHz, but sensitivity falls off terribly below 20KHz. WWVB was clearly audible at 60KHz, but I could not hear any Omega stations around 10KHz. Omega stations were audilble on a Drake TR7 (same antenna), but it has a Hi-Z antenna input. Maybe the 50 Ohm input on the RACAL loads the antenna too much. There were 1KHZ and 10KHz receive options offered on the 6790, and I don't know what was changed other than the firmware. I just thought someone might be interested.
Merry Christmas -Ken Gianino (St. Louis, MO) [email protected]
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Technical manual: (TO 31R2-2URR-251 TM 32-5820-030-14 & P Technical Manual, Combined Operations and Maintenance Instructions with Parts Breakdown (Organizational and Intermediate), Radio Receiver, Type R-2174(P)/URR and R-2174A(P)/URR, Racal Communications, Inc, FO4606-79-D-0082, FO4606-83-C-0535, Rockville MD, (301) 948-4420, (301) 208-7637, (301) 208-7547.
Source: Max-Gain Systems, Inc. Allen Bond -WB4GNT 221 Greencrest Ct. Marietta, Ga. 30068-3825 http://www.aaow.com/mgs/ [email protected]
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This page last updated on January 13, 2000
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