Re[2]: frequency scanners low cost equipment
I recently reviewed the antenna factors for a commercially made overlapping bow tie style antenna and find the factors to be rather high (for example, over 30 dB at many frequencies over 300 MHz). However, it is still a very simple antenna to build, and maybe your scanner will be sensitive enough to compensate for such high losses. Good receivers can detect signals as weak as -15 dBuV. To improve the antenna factors, I would suggest that the overlapping bow ties should be combined with an ordinary corner reflector. I would expect the gain to improve (up to 10dB best case) at frequencies over 50 to 100 MHz for a reasonable size reflector, plus you would benefit from attenuation of unwanted ambient signals from the rear and sides of the antenna. The design requirements are: S = the spacing from the apex of the reflector to the antenna f = frequency (lowest for this case) in MHz. Rule is: minimum S = 0.25(300/f) maximum S = 0.7(300/f) / / -- reflector / / O -- S -- @ -- antenna (in this case, our bow tie antennas) \ \ \ \ The reflector is expected to be a full wavelength (300/f) long, but I suspect you can shorten this to some degree. For 50 MHz, minimum value of S is 150 cm, length is 600 cm. For 100 MHz, minimum value of S is 75 cm, length is 300 cm. For 200 MHz, minimum value of S is 38 cm, length is 150 cm. For 300 MHz, minimum value of S is 25 cm, length is 100 cm. This antenna is simple to build, but it is too large to be built for frequencies approaching 30 MHz. You could still incorporate a large bow tie to capture such frequencies, however. I believe the angle of the reflector should be about 90 degrees. A simple BALUN for this antenna would be just a few common ferrites over the coax near the antenna end of the cable. Still, be careful how the cable moves when moving the antenna. Try to use very low loss coaxial cable such as Belden 9913 to improve overall antenna factors. Other literature may be more helpful, such as the ARRL publications on this topic. Good luck. Eric Lifsey National Instruments
Re: frequency scanners low cost equipment
Thanks for the post, Paul. I'm not trying to mis-state your position, believe me! It's interesting to see what you have to do in order to make your scanner do the job for you. Yes, I found the frequency accuracy of even handheld scanners superior to the HP spectrum analyzers I was using. This is a concern only when dealing with someone who doesn't know they can be expected to differ. On antennas: Almost any antenna you can build will do the job for you. Those concerned with predicting antenna factor from construction need precisely built baluns and elements - but for ordinary measurement, all you need is to calibrate whatever you've built -- assuming it's efficient enough to detect signals below the limit, and that's not hard. Have you seen the antennas now being marketed as 30-1000 MHz antennas? they consist of multiple (three, I think) bow-tie antennas of sheet metal, assembled onto a common feed point. The longest one is actually resonant about 70 MHz, the next appears to be resonant about 100, and the smallest perhaps at 200, but the shape of the plates insures a gently changing impedance versus frequency. As for calibration, I think the most elegant (and acceptable, BTW) way is the three-antenna method, where one measures the site attenuation between three antennas, one pair at a time. This produces a data set contacting all antenna factors, which may be extracted from three simultaneous equations. This _does_ call for three antennas, but you can borrow two of them. Cheers, Cortland == Original Message Follows Date: 12-Feb-97 01:19:09 MsgID: 1044-129130 ToID: 72146,373 From: Paul Rampelbergh INTERNET:rampelberg...@infoboard.be Subj: frequency scanners low cost equipment Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoPart 1 of 1 Hello, Sorry Cortland, I do not allow you to state a position witch I didn't mention subject purpose of utilization range of scanners. The purpose of the use of a scanner was and is for PRE-COMPLIANCE tests in order to find out where the problem areas are before an expensive and complete compliance test. I talk only about the AR8000 from AOR (non commercial advertising). I don't want to open the discussion on the different point of views we had before, but I like to state that the new scanners have good performances as long as you don't want to measure the exact amounts you are below the rule. Linearity for instance has no importance as long as you know the indication below which you have to stay. Anyhow, I think the first step to do in order to find out if the equipment is susceptible to reach compliance, is to have measurements done in not ideal conditions (small shielded enclosure for instance). NOTE: The people who can afford a anechoic chamber don't have to bother about scanners. Its a poor mans solution anyhow! 1. So as you are not, for the first instance, in ideal conditions you gather the disturbing signal frequencies. For this application, the stability and accuracy of a scanner SUPERIOR to older well know expensive equipment's like the Rohde Schwatz generator SMDA - BN 41314, due to the actual technology (phase locked loops crystal). NOTE: Its also, in most of the cases, possible to deduct those freq. from the design but its good to measure it with the scanner just to make sure you get them programmed in for field tests. Modern scanners can memorize the frequencies of interest manually or automatically. 2. Now once you have those frequencies you have to calibrate your receiver (scanner) and there there are some problems. 2.1. Shielding of the receiver is insufficient. Solution: metallic shielding spray or other mechanical means. 2.2. the front end of the receiver do not need pre-tuning, if you have a strong signal close to the frequency you need to measure, you MAY need an external additional input filter to avoid intermodulation. 2.3. You need calibration of the interesting frequencies, the other ones are of NO interest. This is the most difficult part, you need a tests generator, I have the one mentioned above but it needs probably recalibration. 3. The antenna's. Who can tell me how and where I can get the required data to build a Bi-connical antenna for 30 - 200 Mhz frequencies. How much can the calibration deviate from one design to another? The log-periodical antenna is no problem to build, you can find data in the ARRL handbook. Its low cost, use of copper water pipes should do it. Inputs for more data? antenna 4. Now you are able to go to the free air, smell some good cold whether, an measure the previously obtained disturbing frequencies. I was unable to do this due to the stubborn position of our local authorities, not to mention the IBPT (=FCC). To come back on the position of our local authorities
frequency scanners low cost equipment
Hello, Sorry Cortland, I do not allow you to state a position witch I didn't mention subject purpose of utilization range of scanners. The purpose of the use of a scanner was and is for PRE-COMPLIANCE tests in order to find out where the problem areas are before an expensive and complete compliance test. I talk only about the AR8000 from AOR (non commercial advertising). I don't want to open the discussion on the different point of views we had before, but I like to state that the new scanners have good performances as long as you don't want to measure the exact amounts you are below the rule. Linearity for instance has no importance as long as you know the indication below which you have to stay. Anyhow, I think the first step to do in order to find out if the equipment is susceptible to reach compliance, is to have measurements done in not ideal conditions (small shielded enclosure for instance). NOTE: The people who can afford a anechoic chamber don't have to bother about scanners. Its a poor mans solution anyhow! 1. So as you are not, for the first instance, in ideal conditions you gather the disturbing signal frequencies. For this application, the stability and accuracy of a scanner SUPERIOR to older well know expensive equipment's like the Rohde Schwatz generator SMDA - BN 41314, due to the actual technology (phase locked loops crystal). NOTE: Its also, in most of the cases, possible to deduct those freq. from the design but its good to measure it with the scanner just to make sure you get them programmed in for field tests. Modern scanners can memorize the frequencies of interest manually or automatically. 2. Now once you have those frequencies you have to calibrate your receiver (scanner) and there there are some problems. 2.1. Shielding of the receiver is insufficient. Solution: metallic shielding spray or other mechanical means. 2.2. the front end of the receiver do not need pre-tuning, if you have a strong signal close to the frequency you need to measure, you MAY need an external additional input filter to avoid intermodulation. 2.3. You need calibration of the interesting frequencies, the other ones are of NO interest. This is the most difficult part, you need a tests generator, I have the one mentioned above but it needs probably recalibration. 3. The antenna's. Who can tell me how and where I can get the required data to build a Bi-connical antenna for 30 - 200 Mhz frequencies. How much can the calibration deviate from one design to another? The log-periodical antenna is no problem to build, you can find data in the ARRL handbook. Its low cost, use of copper water pipes should do it. Inputs for more data? antenna 4. Now you are able to go to the free air, smell some good cold whether, an measure the previously obtained disturbing frequencies. I was unable to do this due to the stubborn position of our local authorities, not to mention the IBPT (=FCC). To come back on the position of our local authorities. The actual law in Belgium do not allow to have (even if not used) a general converage receiver (a scanner is the sensible point). By the way, the scanner I purchased in the Netherlands (no law restriction) do have the FULL freq. range including cellular phone. Surrounding country's do allow them! In Belgium the concern is that you may be able to listen to the police. I don't know, but I don't think outlaws really take care of the law! The police (and other) equipment who has to be coded and protected, that's the only way out. Now since that discussion with the authorities they claim spectrum analyzers, measurement receivers, test generators, etc.. fall in the OUTLAWED range, you have a speaker on them or you are able listen and to transmit! Good fellows of BIPT. Do you think that other county's know what they are doing? According to our superior BIPT people, NO. How is it possible that for EMC you can, as a manufacturer or as a European representative, do self certification? For telecom equipment you are to stupid to do so, forget it. You need to have a typical Belgium compliance sticking to Belgium typical rules and performed by who? Our magnificent BIPT authorities of course who give it to BELCOMLAB. NOTE: The manager of the security division of the Ministry of Economic affairs states for scanners used in EMC context: According to the Belgium laws the general coverage equipment used as a test equipment is not under control of the IBPT and may be used as long as it is CE approved. The CE approval is only required, as you know, for equipment you sell and not for equipment under test. This people are the once who accepted the EMC proposal without the collaboration of our majesty the BIPT. I hope he will survive the BIPT management autocratic,
Re: frequency scanners low cost equipment
Hello all, thanks for the responses. Still I don't have a clue re: 1. How these scanners are built, any info like block diagrams preferably on the net. How big are they? Do they run on batteries? 2. Where I can buy the ones you recommend. Do the vendors have an internet page? Or at least an address or some way to make contact with them. thanks again moshe valdman
Re: frequency scanners
Hi, If you like to be informed aboud scanners you can subscribe to the mailing list server for the AR8000 from AOR majord...@rpmdp.com with the clasical text: subscribe ar8000 your E-Mail adr. There are also Newsgroups like: rec.radio.scanner or alt.radio.scanner Features example for the AR 8000 from AOR; - frequency range continious without gap from 150 kHz till 1950 Mhz. - frequency steps 50Hz till 500kHz - modes: NFM, AM, USB, LSB, CW, WFM - searches on frequency (specify desired range, step, mode, ..) - scan specific frequencies (individual freq.) - store frequencies to bypass (individual freq.) - attenuator, squelch - configure in between channel wait times - etc.. With the AR8000 (its not the only one of course) its possible to control the features from a PC (in, out and signal strenght data; rs232 connector ttl level; RS232 level converter interface CU8232 or similar). The AR8000 receiver is a triple convertion receiver: 50 ohm BNC input followed by 7 fixed not tunable different input filters : (.1 - 30 Mhz; 30-110; 110-165; 165-240; 240-470;470-820; 820-1950 Mhz) 1st I.F. 736.250 Mhz or 275.450 Mhz depending on freq. range; 2end I.F. 40.05 Mhz monolitic cristal filter 3th I.F. 10.7 Mhz or 456.5 kHz ceramic filter depending on opperating mode; SSB/CW 4 kHz (-6db), 15 kHz (-50db) AM/NFM 12 kHz (-6db), 25 kHz (-60db) WFM 180 kHz (-6db), 800kHz (-50db); For example the AR3000A can be equiped with a SDU5000 Spectrum display unit, etc.. I don't know other brands exept ham radio types, those are not designed for the same purpose and don't have, mostly, the continious frequency range. Hope this give some answer to your request for info Moshe. moshe valdman wrote: I'm interested in the potential use of low cost scanners as low end receivers\spectrum analyzers. My problem is I don't know anything about how they work, Can someone give a brief explanation or/and point me to some technical information (preferably on the web). Regards -- Paul Rampelbergh Wezembeek-Oppem (Belgium) -
Re: frequency scanners
Paul Ramplebergh, in Belgium, is trying to use a scanner for precompliance. He's had some problems with the authorities there -- they don't want to let anyone have a scanner that could receive unlicensed frequencies. I have some problems with using an inexpensive scanner for compliance, but not for engineering and precompliance. Paul, I think, wanted to use his handheld scanner for precision measurement, which is a bit beyond them. That's _my_ view, anyway. I've used several scanners for engineering and precompliance testing. Handheld scanners are much easier to carry out to an EUT than dragging an analyzer on a cart. Desk-type equipment such as Icom and the new AOR -- I'd love to have an AOR 5000 -- would be, IMO, more accurate. However, my objections to scanners run in these lines: 1. Amplitude accuracy is poor. In part, this is a function of the readout, and Paul was going to pull amplitude information out of his using the built-in computer bus. Even high-end scanners such as the Icom R7100 amplitude response varies with frequency; this must be accounted for when trying to get precision readings. Note that Icom 7000 and 7100 use separate, switched front ends for covering the frequency range, and each one must be individually aligned. 2. Bandwidth. I have had two Yupiteru 7100 handheld scanners,and the IF bandwidth (nominal 15 KHz) varied between the two units, with one having rather poor ultimate selectivity. I don't know what the FMBC bandwidth was, as I prefer to use AM mode in troubleshooting, but if it's 180 KHz, it's already a bit wide for EMC measurements. You'd read a bit high on broadband noise. My AOR 8000 is different (netter) yet. The AOR 5000 has the potential of being very useful as its filters may be switched independent of noise. When I get the money I may try one. 3. Inability to take QP. This is a bit of a quibble, the way I use scanners, but if you want to know how many dB you really need, then you'll want to wire in a QP detector. This will also call for disabling the AGC, as otherwise one would be taking the weighted average of a log function rather than of a linear reading. This begins to complicate things, hanging external detectors on the IF and could end up making the whole setup hard to handle. In this country, at least, its difficult ro buy a scanner which is rated to cover all the frequency ranges, with cellular being left out. While this is something people with technical expertise can circumvent, the current legislative climate in Washington may end up doing away with modifiable receivers completely. I don't want to start anything on the scanner/cellphone issue (please!) but I understand one telephone industry representative is urging legislation that would completely pot scanners in plastic to make modification impossible, Aaargh. Anyway... they're useful, No doubt about it. Beyond a certain point -- again, my opinion -- they become less useful. This could be remedied by modifications. One must then ask if a nice piece of surplus EMI gear would be considered more credible,in view of the limitations of consumer grade receivers. That's my two groschen anyway. Cheers, Cortland == Original Message Follows Date: 09-Feb-97 16:01:11 MsgID: 1044-115610 ToID: 72146,373 From: moshe valdman INTERNET:mvald...@netvision.net.il Subj: frequency scanners Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoPart 1 of 1 Sender: owner-emc-p...@mail.ieee.org Received: from ruebert.ieee.org (ruebert.ieee.org [199.172.136.3]) by hil-img -5.compuserve.com (8.6.10/5.950515) id SAA08901; Sun, 9 Feb 1997 18:57:26 -0500 Received: (from daemon@localhost) by ruebert.ieee.org (8.7.5/8.7.3) id RAA24645 for emc-pstc-list; Sun, 9 Feb 1997 17:16:20 -0500 (EST) List-Post: emc-pstc@listserv.ieee.org Date: Mon, 10 Feb 97 00:08:42 PST From: moshe valdman mvald...@netvision.net.il Subject: frequency scanners To: emc-p...@ieee.org X-Mailer: Chameleon V0.05, TCP/IP for Windows, NetManage Inc. Message-ID: chameleon.97021940.mvald...@dialup.netvision.net.il MIME-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Sender: owner-emc-p...@majordomo.ieee.org Precedence: bulk Reply-To: moshe valdman mvald...@netvision.net.il X-Resent-To: Multiple Recipients emc-p...@majordomo.ieee.org X-Listname: emc-pstc X-List-Description: Product Safety Tech. Committee, EMC Society X-Info: Help requests to emc-pstc-requ...@majordomo.ieee.org X-Info: [Un]Subscribe requests to majord...@majordomo.ieee.org X-Moderator-Address: emc-pstc-appro...@majordomo.ieee.org Hello again, I'm interested in the potential use of low cost scanners as low end receivers\spectrum analyzers. My problem is I don't know anything about how they work, what are the inherent limitations (freq accuracy, amplitude accuracy etc). I'm thinking of course ! about the synthesised ones where you don't have a xtal per each frequency. Can someone give a brief
frequency scanners
Hello again, I'm interested in the potential use of low cost scanners as low end receivers\spectrum analyzers. My problem is I don't know anything about how they work, what are the inherent limitations (freq accuracy, amplitude accuracy etc). I'm thinking of course about the synthesised ones where you don't have a xtal per each frequency. Can someone give a brief explanation or/and point me to some technical information (preferably on the web). thanks - Name: moshe valdman E-mail: mvald...@mail.netvision.net.il List-Post: emc-pstc@listserv.ieee.org Date: 02/06/97 Time: 00:29:57 This message was sent by Chameleon - --End of Original Message--
